Chapter 6: AAF Aircraft of World War II
THE AAF fought during World War II with aircraft which were all either in production or under development prior to 7 December 1941. An unavoidable time lag exists between the conception of a weapon and its tactical use, and this is particularly true of such a complex machine as the modern combat plane. Despite intensive efforts during the war to shorten the interval, the lag was rarely less than three and often as much as five or more years. The major wartime achievements in research and development – for example, jet propulsion – had their chief effect on the tactical strength of the air force only after the war was over. But if the AAF necessarily fought with prewar types of aircraft, a multitude of modifications made the AAF’s 1945 planes far superior to their 1941 and 1942 predecessors.
The more highly publicized planes, such as the B-17 and the P-47, became familiar to the American public according to a conventional mode of designation that combined a letter as the symbol of function with a numeral to indicate sequence within a type. In these designations, A stood for Attack, B for Bombardment, C for Cargo (transport), F for Photographic, L for Liaison, P for Pursuit (fighter), and T for Training (the prefix of P, B, or A indicated Primary, Basic, and Advanced). The men who flew in combat, and who thus knew at first hand the desperate need to counter each tactical or technical advance by the enemy, gave closer attention to the letter appended after the numeral to indicate the model, for the B-17E incorporated improvements over the earlier B-17D. Only as a plane reached the state of obsolescence did the AAF leave off in a continuing effort to improve its performance and its equipment.
In the development of improved equipment the primary responsibility
might lie in agencies outside the AAF. The application of radar to problems of navigation and target identification undoubtedly represented the most significant advance of the war years, but for the development of radar devices of all sorts the AAF looked to the Signal Corps until late in 1944. Similarly, the Ordnance Department of the Army carried the responsibility for armament employed in aircraft – a field in which the chief progress during the war came in the use of guns of heavier caliber and in larger numbers. Although an armament conference of Air Corps leaders meeting in December 1939 had emphasized the need for development of weapons specifically designed for use in the airplane, the AAF in 1941 was still basically dependent, bombs alone excepted, upon adaptations of weapons originally designed for ground or naval use.1 Of these the .50-caliber machine gun ranked first in importance. But if responsibility in significant areas of development was thus divided, there was no division in so far as the airplane itself was concerned. For the airframe, for its armor, and for its motive force, and for such developments as the power-driven turret and a central control of firepower, the responsibility was clearly fixed within the AAF.
The military aircraft of World War II was a monoplane with one to four engines and an aluminum airframe housing a mass of equipment for the purposes of navigation, armament, communication, and crew accommodation. The power plant and its accompanying propeller were the keys to aircraft performance, for speed, range, altitude, and rate of climb depended in large measure on the power and efficiency of the propulsion unit. The race to increase the power ratings of existing engines and to develop new ones was among the most significant competitions of the war.*
World War II aircraft were powered by multi-cylinder, reciprocating
* The improvement achieved is suggested by the following table:
| Original Take-off | 1945 Take-off | |
| Engines | Horsepower Rating | Horsepower Rating |
| Packard V-1650 | 1,300 | 1,700 |
| Allison V-1710 | 1,000 | 1,700 |
| Wright R-1820 | 750 | 1,350 |
| Pratt & Whitney R-1830 | 950 | 1,350 |
| Wright R-2600 | 1,500 | 1,800 |
| Pratt & Whitney R-2800 | 1,800 | 2,100 |
| Wright R-3350 | 2,800 | 2,500 |
The maximum horsepower actually in use in 1945 was somewhat lower than shown above because the engines with the 1945 take-off ratings were usually not yet incorporated in combat models.
engines. Heavier planes which required more powerful engines became still heavier with the installation of larger engines. In the effort to secure maximum power with a minimum weight, engines, like the planes they served, went through many changes. The Pratt & Whitney R-1830 engine* went through six major and some eighteen minor variations, making a total of twenty-four models, none of them completely interchangeable.2 Although the P-35 and P-36, standard fighters of the late 1930’s, had been powered by air-cooled radial engines, the P-38, P-39, P-40, P-47, and P-51 were all originally designed around the liquid-cooled in-line or V-type engine.3 The liquid-cooled engine was more compact than the air-cooled radial engine, and it had a larger horsepower output per unit of frontal area, an important consideration in aircraft design.† In addition, liquid-cooled engines consumed fuel more efficiently than did air-cooled ones.4
Two developments perfected during the 1930’s – the supercharger and the controllable-pitch constant-speed propeller – played important parts in increasing the efficiency of the aircraft engine. The controllable-pitch constant-speed propeller could be set to maintain any chosen engine speed and thereby permitted maximum utilization of available engine power under all conditions. The supercharger, a device for increasing the mass air charge of an internal combustion engine over that which would normally be drawn in by the pistons, is used to compensate for the lower density of air at high altitudes. It was the supercharger, either as an integral part of or as a separate unit attached to increasingly powerful engines, which permitted the
* The AAF designated its engines thus by letter and number-the letter R indicating a radial arrangement of the cylinders, the letter V an in-line V-type arrangement. The number was fixed by the cubic-inch piston displacement.
† The only American manufacturer of liquid-cooled engines for military purposes in 1939 was the Allison Division of General Motors, which was just bringing its V-1710 engine into production. The success of the British with the Rolls Royce Merlin engine and the obvious desirability of having another source of production persuaded the Air Corps to initiate production of the Merlin engine in the United States in 1940. The Packard Motor Car Company manufactured the engine as the V-1650, beginning in 1941, after an “extraordinarily rapid and excellent job of redrawing the engine to conform to American production standards and practices.” But because the air-cooled engine had certain advantages over the liquid-cooled one, including less vulnerability, more durability, and easier maintenance, the Air Corps did not rule out its use in fighter planes. The development of the R-2800 engine (used with great success in the P-47) by Pratt & Whitney provided an outstanding air-cooled engine with a potential great enough eventually to make it at least the equal in performance of any liquid-cooled engine.
operation of AAF bombers and fighters at greater speeds and higher altitudes.
By the end of hostilities all heavy bombers had achieved a ceiling of more than 30,000 feet and that of the B-29 approached 40,000. Similarly, speed had been increased and range extended. The 300 miles per hour maximum and 600 miles combat range of the P-36 in 1939 contrasted sharply with the almost 500 miles per hour of the P-51H and the better than 2,000-mile range of the P-47N in 1945. In 1939 the B-17B was credited with a high speed of 268 miles per hour and a combat range of 1,000 miles. In 1945 the B-29B, more than twice as large as the B-17B, had a top speed of almost 400 miles per hour and a combat range approaching 4,000 miles.5 The intervening years, whatever the failures may have been, had been nevertheless years of startling achievement.
It is difficult to draw a satisfactory line between the most general description of a plane and detailed tabulation of specific models. The difficulty becomes the greater because so much of the critical data on performance acquires practical meaning only when considered in relation to the varied requirements of combat. Performance characteristics are generally given in terms of maximum capabilities under ideal conditions and can be misleading as to performance under battle conditions. An aircraft may have a top speed of 300 miles per hour, a ceiling of 30,000 feet, a maximum or ferrying range of 3,000 miles, and a maximum bomb load of 8,000 pounds, but it cannot achieve all of these maximums in a single flight, even under ideal conditions. In order to fly 3,000 miles, it must carry a maximum fuel load and no bombs, and it must cruise at a moderate rate of speed to conserve fuel. The effective range under battle conditions, for example, thus becomes something quite different from the full potential considered without reference to military obligations. Statistics of maximum performance in the several categories nevertheless offer useful guidance as to the relative potential of different planes for any type of employment.*
* It may be helpful for the reader to bear in mind the following definitions. The range of a plane is the total distance it can fly without refueling. Its maximum range is a ferrying range, which is to say that the additional range is secured by using all available space for added fuel. The combat range is necessarily somewhat less than the maximum range because the plane is combat-loaded – that is, it carries bombs and other items required for combat in lieu of additional fuel. The tactical radius of a plane is the maximum distance it can fly away from its base with a normal combat load and return without refueling, allowing for all safety and operating factors. For practical purposes during World War II, tactical radius was considered to be three-eighths to two-fifths of the combat range. These figures were considerably less than half the combat range because of allowances for certain factors – including fuel reserves, time required for assembly of formations, and time in the combat zone – which were not included in the computation of combat range. Both combat range and tactical radius vary with the loading of the plane.
All told, the AAF employed more than a hundred aircraft models during World War II. At its peak strength in July 1944, it had on hand 79,908 planes of all types.6 In the following pages the more important of these planes will be discussed in terms of their conventional classification.
Attack and Bombardment
Although opinion in the AAF placed special stress on strategic bombardment as the prime mission of an air force, the dominant view in the War Department General Staff was officially stated as late as October 1938 in these terms: “the Infantry Division continues to be the basic combat element by which battles are won, the necessary enemy field forces destroyed, and captured territory held.”7 It followed that the primary function of Army aviation was the support of ground forces in battle. And from this emphasis came the influences which gave shape to the A-20, the A-26, and the more famous B-25 and B-26, all of them designed basically for a supporting mission.
The attack plane, first so designated in 1922 and frequently described as a light bomber, was designed for immediate support of ground troops. Because it was to operate chiefly at low altitude, a premium was placed on high speed and maneuverability. Armed with bombs and machine guns, its development during the war years tended to carry the plane closer to the classification of the medium bomber, especially after fighter aircraft proved particularly effective in the combined functions of a fighter-bomber. The medium bomber, considered to be a “pure bombardment type,” was intended to operate at medium altitudes of 8,000 to 14,000 feet and primarily against depots, fortified positions, railroad yards, and other such targets along or behind the battle line.8 Carrying a heavier bomb load and enjoying the advantage of greater range, the mediums could supplement the work of light bombers and might assist the long-range heavy bombers against the nearer targets in a strategic bombardment effort.
The A-20, or the Havoc, was developed from the Douglas DB-7, originally designed for the French Air Force in 1937. Its prototype was test-flown in 1938; production began the next year; and during 1940 the Air Corps accepted almost 300 A-20’s, most of them for release to the British, who called the planes Bostons and put them to good use in North Africa.9 The AAF used the A-20 in most theaters of operations during the war, and had a peak inventory of more than 1,700 of the planes in September 1944, but of the 7,385 A-20’s accepted between 1940 and 1944, a substantial number were allocated to the British and the Russians.10 Production of A-20’s was discontinued late in 1944, when the superior. A-26 became available in sufficient numbers to begin replacement of the A-20 in combat units.11
The A-20, of which there were eight major models, was a mid-wing all-metal monoplane powered by two Wright R-2600 engines. With improved engines, the airframe weight of the plane increased from 8,600 pounds in 1941 to 10,800 pounds in 1944, while the maximum weight (including bombs and crew) increased from some 21,000 pounds to 30,000 pounds. The armament was also increased – from seven .30-caliber machine guns in 1941 to as many as nine .50-caliber machine guns in 1944–45. Some of the later A-20’s carried five .50-caliber machine guns and up to twelve 5-inch rockets. The bomb load was increased from a maximum of 2,400 pounds in 1941 to 4,000 pounds in 1944–45, carried both internally and externally. There was little increase in the maximum speed (325 miles per hour) or the tactical radius of the A-20 during the war, largely because of the increase in weight without a proportional increase in engine power. The normal tactical radius with 2,000 pounds of bombs was 250 miles.12 It carried a three-man crew.
The early success of the German Stuka led AAF leaders to consider redesigning the A-20 as a dive bomber, but the technical difficulties proved to be too great. Efforts to convert Navy dive bombers to meet Air Corps needs were then pushed, but when the chief product of these efforts, the single-engine A-24 (Navy SBD-3), was combat-tested in New Guinea, it was considered by Army airmen to be too slow, too limited in range, and too vulnerable to enemy fighters.13 In the spring of 1942 it was decided that the P-51, a new fighter that had gone into production the preceding year and for which the AAF as yet had no major plans, could be converted
into a dive bomber. With added diving brakes* and external wing bomb racks carrying up to 1,000 pounds, and with changes of armament and engine, the modified P-51 became the A-36.14 By early 1943 two groups had been equipped for service in the Mediterranean, where they performed well enough but where experience also demonstrated that the value of this specialized plane had been overestimated. The more versatile fighter-bomber – a straight fighter equipped with bomb racks – proved much more useful. By V-J Day the A-36 had completely disappeared from AAF inventories.15
The B-25 (Mitchell) and the B-26 (Marauder), each operating with six-man crews, served as the AAF’s medium bombers during the greater part of World War II. North American had initiated design on the B-25 in February 1938 and production began in February 1941, without benefit of an experimental prototype plane.16 Similarly, the Air Corps bought the B-26 from the Glenn L. Martin Company right off the drawing board in 1939: a production contract was signed in September of that year, the first plane flew in November 1940, and manufacture got under way at approximately the same time as that of the B-25.17 Since the Mitchell was being produced in quantity at an earlier date, it was the first to reach the combat areas in substantial numbers.18 After its use on Doolittle’s Tokyo raid in the spring of 1942, only the highly publicized B-17 was better known to the American public. In all, the AAF accepted 9,816 B-25’s and 5,157 B-26’s; a large number of the B-25’s accepted were intended for British and Russian use. The peak AAF inventory for the B-25 was 2,656 in July 1944, and for the B-26, 1,931 in March 1944. After January 1944 B-25 and B-26 groups within the AAF were approximately equal in number. B-26 production ceased in April 1945 and B-25 production came to an end shortly after V-J Day.19
Both planes were twin-engine all-metal mid-wing monoplanes. In 1941 the Mitchell’s two R-2600 engines gave it a maximum take-off power rating of 3,400 horsepower as compared with the Marauder’s 3,700. In 1945 the raring for the Mitchell had not been increased, but that of the Marauder had been stepped up to 4,000. During the same period the airframe weight of the B-25 was increased from 11,600 pounds to 13,000 pounds and the maximum weight from
* Apparently the brakes were not satisfactory, for they were wired shut and all dives were made without brakes.
25,000 to 35,000 pounds. The Marauder, a larger plane to begin with, grew from an original airframe weight of 14,100 pounds to almost 17,000 pounds, while its maximum went from 33,000 pounds to more than 38,000. The five machine guns mounted on the 1941 models of the two planes were increased to as many as fourteen .50-caliber guns on some B-25’s and twelve on the other plane. Some of the B-25’s were equipped with a 75-mm. cannon in the nose of the plane in addition to a half-dozen machine guns. The B-26 was the first American bomber designed with a gun turret, and the B-25 had turrets incorporated, beginning with the B-25B. Normal bomb loads were about 2,400 pounds in 1941 and 4,000 pounds in 1945.20 As with the A-20, the speeds of the B-25 and B-26 were not measurably increased during the war. The maximum speed for the B-25 at normal combat weight in 1945 (33,500 pounds) was 285 miles per hour, and for the B-26 (at 37,000 pounds) it was about the same. Because of the considerable differences in total weight and in bomb loads carried, it is difficult to compare accurately the 1941 and 1945 ranges of these planes. By 1945 the combat range of the B-25 with a 3,200-pound bomb load was 1,200 miles and for the B-26 with a 4,000-pound load, 1,100 miles.21 The significant factor in medium bombardment operations, it might be noted, is the size of the bomb load and not the range.
The B-25 ranked consistently as a favorite among AAF pilots, but the B-26 was promptly dubbed the “Widow Maker” and the “Flying Prostitute.” Trouble experienced from the first delivery of the plane early in 1941 so persisted that only one combat group (the 22nd Bombardment Group, soon sent to Australia) had been equipped with the B-26 by December of that year.22 As accidents, some of them fatal, continued, General Arnold at the end of March 1942 appointed a special investigating board headed by Maj. Gen. Carl Spaatz to determine whether production should be continued. The board recommended several changes in the plane’s design (the chief being a larger wing) and continued use of the plane.23 Manufacture of the B-26, which had been suspended until necessary changes had been made, was resumed in May, but in July and once again in October 1942 the AAF gave serious consideration to scrapping the B-26 in favor of some other type of plane.24 But Maj. Gen. George C. Kenney, on the basis of experience in SWPA, commended the plane to Arnold,25 and before the end of the year B-26 units were
operating successfully in North Africa. After tripping over one final hurdle, a tragic miscarriage of one of the earliest B-26 missions from England that led to further discussion of abandoning the plane,26 the B-26 won full approval. A “hot” plane with a fast landing speed, it more than proved its worth after experience and intensified training taught pilots how to handle it.
Despite its designation, the A-26 (Invader), which first appeared in combat in 1944, was the most advanced medium bomber used by the AAF during the war. Douglas began designing the plane in January 1941, building the new model on the best features of the DB-7 and the A-20 but with plans for a much greater range and bomb load. Flown first in July 1942, the A-26 went into production in September 1943. By May 1945 six A-26 groups had been committed in overseas theaters. Acceptances of the plane reached almost 2,500 by August 1945.27
The Invader was an all-metal mid-wing monoplane powered by two Pratt & Whitney R-2800 engines, the same power plant used in the B-26. With a combat weight of 35,000 pounds, the A-26 could fly at 360 miles per hour, more than 60 miles faster than the other medium bombers. Its combat range reached 1,000 miles, with a bomb load of 4,000 pounds and a three-man crew. Formidably armed with eighteen .50-caliber machine guns and fourteen 5-inch rockets, the plane had a maximum bomb load of 6,000 pounds, two-thirds of it carried internally.28
As early as 1942 the AAF planned to replace all other mediums with the A-26.* But production delays, for which AAF Headquarters was inclined to blame the Douglas Company, kept acceptances to a total of only twenty-one planes by 1 March 1944. Arnold’s insistence that he wanted the plane “for use in this war and not for the next war” helped to overcome certain shortages of machine tools, and after July 1944 production mounted steadily.29 Though a late comer, the A-26 compiled a distinguished combat record and, after a period of uncertainty in 1944, won ready acceptance from the crews who flew it. In the postwar period, the A-26 became the Air Force’s standard tactical bomber. Redesignated as the B-26 in 1947, it was to be heavily relied on three years later in Korea.
* Experiments were also made to test the possibility that a converted version of the plane might do as a night fighter.
The Big Bomber
Interest among American airmen in the development of a “big bomber” extended back to the early 1920’s. Plans for a night bomber with a cruising radius up to 1,000 miles, and a payload of 10,000 pounds, had led in 1923 to the Barling bomber – the largest plane built in the United States up to that time. A triplane with a gross weight of more than 42,000 pounds, its six Liberty 12-A engines proved unequal to the task of achieving a speed even of 100 miles per hour; nor could they lift the plane across the Appalachians for the 400-mile flight from Dayton to Washington. But the venture provided useful engineering data, emphasizing especially the ratio that must be observed between the size of a plane and the power generated by its engines.30 For the remainder of the decade nothing more ambitious than a twin-engine plane was attempted. By the 1930’s, however, great progress had been made in the field of aerodynamics and improvements of design had brought the monoplane with its many advantages. Public policy, moreover, opened the way between 1931 and 1935 for the Air Corps to undertake responsibilities of coastal defense that would justify the development of a long-range bomber.
The planners showed some tendency, again, to get ahead of the engineers. The Materiel Division in 1933 set the objective in terms of a plane with a range of 5,000 miles at a speed of 200 miles per hour with a bomb load of 2,000 pounds. War Department approval having given the development plan official status as Project A, contracts of 1934 and 1935 with Boeing resulted in the construction of one experimental model, completed in the fall of 1937 as the XB-15.* Its gross weight of 70,000 pounds was too great for its four 1,000-horsepower engines; its top speed of 190 miles per hour was less than had been hoped for, and its high fuel consumption did not permit it to approach the range projected for it. An Air Corps proposal to modify the plane and produce a model called the YB-20† was disapproved by the Assistant Secretary of War.31 Another contract of 1935, this time with the Douglas Aircraft Company, produced in June 1941 the XB-19 – the largest of all bombers prior to the B-36. Neither the four 2,200-horsepower motors originally installed
* See Vol I, pp. [.usaaf01 65-66].
† The prefix Y indicated planes intended for service testing.
nor the four of 2,600 horsepower each subsequently tried provided the lift required by its 160,000 pounds maximum gross weight.32 The B-19, like the B-15, served only to test, and thus to advance, the engineering knowledge that went into the construction of other and more successful planes.
The B-17, built by Boeing to less ambitious specifications submitted in a design competition for a multi-engine bomber in 1933–34, was the first of the Air Corps’ “big bombers.” Flown originally in July 1935, the plane had a gross weight of 40,000 pounds and four 750-horsepower engines. The tragic loss, through crash and burning, of the first model in the fall of 1935 forced the Air Corps, which had been much impressed by the plane’s performance, to reduce a planned purchase of sixty-five of the aircraft to only thirteen, all of which had been delivered by August 1937.33
Convinced that it had in the B-17 the best bomber in the world, the Air Corps was anxious to purchase the plane in quantity for equipment of the GHQ Air Force. Procurement estimates for fiscal year 1938, submitted to the War Department in 1936, recommended the establishment of at least two B-17 groups – one to be stationed on the east coast and one on the west. Place should be found in the 1938 budget for fifty B-17’s, in supplement to the twenty-six already authorized for 1937, and for eleven Project A planes as tokens of a policy of continuing development and production. But a special study by G-4, prepared at the request of the Secretary of War, brought in June 1936 a most discouraging statement of War Department policy.34 Concentration on the big bomber, an offensive weapon, was inconsistent with national policy and threatened unnecessary duplication of function with the Navy, whose eleven carrier-based bombing squadrons equaled the combined total of such forces elsewhere in the world. No country had at the time, or was likely to have in the near future, aircraft capable of mounting an air attack on the United States. And since aircraft of medium range were “capable of attacking” any hostile naval or land-based aviation within effective range of our vital strategic areas, the request for the much more expensive long-range planes lacked logic. The B-18, then the standard two-engine bomber, was equal to any mission assigned the Air Corps and was much less expensive. Not only did the study advise against the purchase of the requested B-17’s but, in a reversal of the attitude more recently governing policy, the paper argued
against the development of “long-range, high-cost, bombardment airplanes” of the Project A type. Until the international situation indicated a “need for long-range bombardment aviation,” the Air Corps should be equipped with “airplanes of reasonable performances rather than to have nothing as a result of our efforts to reach for the ideal.”
These views as to Army aircraft requirements were to prevail against Air Corps arguments until the logic of events destroyed the assumptions on which the analysis was based. When President Roosevelt added the weight of his own insistence upon a greatly expanded program of aircraft production in the autumn of 1938,* the Air Corps’ only long-range bombers were the original thirteen B-17’s. An early addition to bomber strength was promised by a total of forty aircraft on order at the end of that year.35 General Andrews, commanding the GHQ Air Force, had recommended in 1937 that his bombardment units henceforth should be equipped only with four-engine bombers,36 but that force would not begin to be equipped with the B-17 until the summer of 1939.37 During the calendar year of 1940 factory acceptances of heavy bombers totaled 60 aircraft (53 B-17’s and 7 B-24’s); for 1941 the total reached 313 (144 B-17’s and 169 B-24’s).38 At the opening of hostilities in December of that year, official figures for heavy bombers on hand in the AAF were just under 300.39
Although the Air Corps by 1938 had won approval of the B-17 as a standard model for use in combat units, the War Department as late as October of that year specified that production of four-engine bombers should not be included in estimates for fiscal 1940 and 1941.40 Also, in response to a request for funds to underwrite the development of a pressurized-cabin bomber with a ceiling of 30,000 feet and a range of 4,000 miles, the War Department had replied in August 1938 that “experimentation and development for fiscal years 1939 and 1940 will be restricted to that class of aviation designed for the close support of ground troops. ... “41 But the President’s newly awakened interest in aviation soon removed all such barriers to the attainment of Air Corps hopes. Valuable time had been lost, but the experimental models of the B-17 already gave proof that the day of the big bomber had come.
The delay in getting the plane into quantity production must be
* See above, pp. 9-10 .
A-24 Douglas Dauntless
A-20 Douglas Havoc
A-26 Douglas Invader
attributed in part to continuing experimentation for the improvement of its performance. Series A, B, C, and D all predated Pearl Harbor – the planes which carried destruction to Germany were B-17E’s, F’s, and G’s, and chiefly the last two. The B-17B, the first assigned to combat units, had an airframe weight of 18,700 pounds, a maximum gross weight well in excess of 40,000 pounds, and could carry a maximum bomb load of 8,800 pounds – which it rarely did. Powered by four Wright R-1820–51 engines of 1,000 horsepower each, the plane had a maximum speed of 268 miles an hour and a cruising speed of 230 miles per hour at an altitude of 25,000 feet; at 10,000 feet the speeds were 233 and 176 respectively. Obviously, operation at high altitudes was extremely important if maximum speed was to be obtained, not to mention the additional encouragement to raise the ceiling subsequently provided by enemy fighter planes and antiaircraft. The B-17B had a maximum range of 3,000 miles, but its combat range with a bomb load of 2,400 pounds was less than 1,500 miles.* This meant a radius of little more than 600 miles. For armament the plane carried only five flexible machine guns, all of them .30-caliber initially – hardly enough to justify its popular designation as the Flying Fortress.42
The installation of superchargers on the B-17B raised the ceiling 10,000 feet over that of the original 1935 model. Further refinements of supercharger and engine (the horsepower reached 1,200 during the course of the war) gave the B-17G in 1945 an operating ceiling of more than 30,000 feet and a top speed of some 300 miles per hour.43 The problem of increasing range without sacrificing bomb load continued to challenge the attention of engineers and combat leaders alike. From the early B-17’s of 1939 to the B-17F and G, the fuel capacity was more than doubled – from 1,700 gallons† to more than 3,600 gallons. This doubling of fuel capacity could not result in a comparable extension of range, for the fuel and other changes added their own weight to the load that must be carried, but the radius of action was markedly extended. While the B-17C and D were credited with a range of 1,280 miles carrying a bomb load of 2,400 pounds, the B-17F and G, with a bomb load of 4,000
* Prewar statistics on range of aircraft were generally found to be exaggerated when actual wartime experience brought home to the AAF the great host of factors affecting combat radius of action.
† In 1941 the B-17B’s had a maximum fuel capacity of almost 2,500 gallons.
pounds, had a combat range of better than 2,000 miles.44 The B-17B carried two .30-caliber and three .50-caliber machine guns in 1941; in 1945 the B-17F and G carried twelve .50-caliber machine guns, four of them housed in upper and lower power-driven turrets, features not found in the earlier models. Other additions included protective armor, bullet-proof windshields, and various types of equipment for communication, navigation, and flight control. The bomb loading depended on the type of bomb carried – the B-17F and G could carry only two 2,000-pound bombs, but there was room for eight 1,600-pound or 1,000-pound bombs. The quantity of smaller bombs that could be loaded varied.45
A typical mission by B-17’s in the European theater in 1944–45 would take them to Berlin, Munich, or Leipzig. From their airfields in East Anglia the bombers would have a practical radius of some 600 to 700 miles with a bomb load of 4,000 to 5,000 pounds. Longer missions were occasionally flown to targets like Danzig and Warsaw, but these were with reduced bomb loads. For most combat purposes then, the effective combat radius of the B-17 may be stated as less than 800 miles.46
The B-17, although the first of the country’s heavy bombers, was not produced in as great quantity as was the B-24. Between January 1940 and 31 August 1945 the AAF accepted a total of 12,692 B-17’s and 18,190 B-24’s.* The peak AAF inventory for B-17’s was 4,574 in August 1944, and for B-24’s, 6,043 in September 1944.47 The maximum number of overseas combat groups was thirty-three for the B-17 in September 1944 and forty-five and one-half for the B-24 in June 1944. Both planes were used in virtually every theater of war, but, in general, the B-17’s were concentrated in the European and Mediterranean theaters and the B-24’s in the Mediterranean and Pacific theaters.48
The B-24 represented one of the earliest products of President Roosevelt’s intervention in behalf of air power in the autumn of 1938. Taking advantage of the new authority for heavy bomber development, General Arnold in January 1939 asked the Consolidated Aircraft Company to produce a four-engine bomber with a 3,000-mile range, a top speed above 300 miles per hour, and a ceiling of 35,000 feet. These specifications exceeded current B-17
* Of these last, a large number went to Allied countries, and the Navy took nearly 1,000 (see Vol I, p. [.usaaf01 551n]).
characteristics, and it was hoped that a superior plane might be the result. On the basis of preliminary engineering data, the Air Corps contracted in March 1939 for a prototype to be produced by the end of that year.49 Drawing heavily upon experience with the B-15 and the B-17, Consolidated had the new plane ready for its first test-flight at San Diego in December. Already the Air Corps, losing no chance to speed its preparation for war, had contracted for seven YB-24’s and thirty-six B-24A’s.50 The plane went into production in 1941.
Like the B-17, the B-24 underwent many modifications. Production models actually reached the B-24M, and model N was under development at the close of the war. Quantity production came with model D, and on the battle fronts D, H, and J became the most familiar. The B-24D carried the turbo-supercharger. Additional armor, self-sealing fuel tanks, power-operated gun turrets, and improved flight equipment may be listed among the major changes. Ten .50-caliber machine guns replaced the original three .50-caliber and four .30-caliber guns. The maximum bomb load rose from 8,800 pounds to 12,800.51 The speed remained comparable to that of the B-17.
The most distinctive feature of the B-24 was its twin-tail construction. As early as 1942 the AAF felt that a single-tail B-24 would provide greater stability, and Consolidated undertook to try the change. Test models flown in 1943 produced results that led in April 1944 to a decision that all future B-24’s would have the single tail.52 Actually, the Navy got most of the newly designed Liberators,* and on Army fields the familiar twin-tail remained the distinguishing feature of the B-24. An ungainly looking ship on the ground, it had a grace of its own in the air. The number of B-24’s produced during the war years, which reached a higher figure than that for any other U.S. combat aircraft, testifies to the plane’s continuing utility in a wide variety of roles, including those of tanker and transport as well as bomber.
The B-17 and the B-24 inevitably invited comparison. Coming along four to five years after the B-17, the B-24 possessed an initial advantage. It carried a larger bomb load than the B-17 and could carry the load farther with a crew of the same size-ten men. Listed in the charts originally as having a range of 2,850 miles with a 2,500-pound bomb load, experience showed that it did have a longer reach than any other compering plane.53 It was this advantage that gave the
* Called Privateers or PB4Y2’s.
B-24 the call over the B-17 for service in CBI and SWPA, where Kenney’s Fifth Air Force used it for the 2,400-mile round trip attacks on Balikpapan in 1944,* and where regularly, if less spectacularly, it extended the coverage of overwater search. Against the German Air Force, however, combat experience showed the plane to be lacking in armament and armor. Attempts to remedy these and other short-comings increased the weight of the plane and altered flight characteristics in such a way as to render it less stable. Lt. Gen. James H. Doolittle, commanding the Eighth Air Force, made his preference for the B-17 clear in a letter of January 1945.54 By that date the increased range of the B-17 some time since had robbed the B-24 of its chief advantage.55 Against the Luftwaffe, the capital enemy, the rugged and steady B-17 remained the natural pick.
The B-29, whose size and performance justified its classification as a Very Heavy (VHB) or Very Long-Range (VLR) bomber, was the largest bombardment plane employed by any belligerent during World War II. Flying first from China and later from the Marianas, the plane repeatedly proved its capacity to deliver payloads up to 15,000 pounds against Japanese targets at a distance of as much as 1,600 statute miles from base. The story of the plane, and of the tactical and technical changes which made this achievement possible, has been recounted in an earlier volume of this series.† Here it will be sufficient to summarize somewhat briefly for the convenience of the reader.
Having acted to assure the necessary provision of bombardment planes built to more modest specifications, the AAF turned its attention to the realization of a goal as old as Project A‡ – the building of a really big bomber. Practical experience argued against any attempt to take too high a hurdle at once, and the original specifications submitted to manufacturers in January 1940 were below those for the as yet unfinished B-19. Contracts for experimental models were completed with Boeing and Consolidated on 6 September 1940, the projected models receiving designations, respectively, as the XB-29 and the XB-32.56 Both planes were test-flown for the first time in September
* See Vol. V, 316-22. In the war against Germany, the plane’s most famous mission was that flown from Africa against Ploesti in August 1943 (see Vol. II, [.usaaf02 477-84]).
† In Vol. V, Sections I and IV. See especially [.usaaf05 chapter01 Chapter I] for the origins of the VLR project.
‡ See above, p. 202.
1942, but successive delays in getting the B-32 into production gave it an insignificant place in the combat history of the war.* In contrast, though there were discouraging delays, the B-29 set a remarkable combat record within four years of the original experimental contract. Boeing made the first delivery, of seven planes, in July 1943. By the end of August 1945 acceptances had reached a total of 3,763. AAF inventories that month showed 2,132 of the aircraft on hand, of which number over 1,000 then belonged to the Marianas-based Twentieth Air Force. At the end of the war forty B-29 groups had been organized, and of these twenty-one had reached their combat stations in the Pacific.57
This remarkable record could not have been achieved except for the willingness of Arnold and Lovett to gamble. In the first move of “the three-billion-dollar gamble,” the AAF entered into a contract for the plane’s production long before it had been flight-tested; in September 1942 contracts had been let for 1,644 planes.58 The full extent of the risk may be somewhat more exactly suggested by noting that the materials, measured by weight, required for one B-29 airframe equaled the requirement for eleven P-51’s.59 It was a gamble not so much with money, of which a wartime plenty existed, as with the allocation of scarce materials and manufacturing facilities. Boeing’s existing plants were heavily committed to production of the indispensable B-17, so that for the B-29 program new factories at Renton in Washington and at Wichita in Kansas had to be built. It having been recognized that Boeing, even with greatly expanded facilities, could not carry the full load, the Bell Aircraft and Glenn L. Martin companies took part of the load at newly constructed and government-financed plants located, respectively, at Marietta, Georgia, and at Omaha, Nebraska.†.60
The old problem of providing a motive force adequate to the size of the plane-which doubled the weight of the B-17-was ultimately solved by the Wright R-3350 engine. Even with a maximum horsepower almost double that generated by the engines of the B-17, the R-3350 could not meet the demand until further streamlining of the plane had been accomplished. The first quantity production order for the plane had been closed in 1941, but efforts to correct defects and
* See below, pp. 210-11.
† At the end of August 1945 the production record stood as follows: Wichita, 1,595; Renton, 998; Marietta, 652; Omaha, 515. The original three B-29’s had been built at Boeing’s Seattle plant.
to improve performance of the engine continued to be a major factor affecting plans for combat use of the plane for three years thereafter. In the B-29 the AAF secured at last its pressurized-cabin bomber. Among other new features, the chief was a central fire-control system. The usual armament was twelve .50-caliber machine guns, or ten machine guns and a 20-mm. cannon, all mounted in power-driven turrets.61 Three models were used in combat: the B-29, B-29A, and B-29B. The bomb load – up to 20,000 pounds – was all carried internally. The crew included eleven men. A maximum fuel capacity of 9,548 gallons gave the B-29B a maximum range well over the 5,000-mile goal of Project A.62 The justifiable satisfaction with which the AAF at war’s end viewed the combat record of this plane came in no small part from the confirmation that record gave to a long-cherished faith in the practicability of the big bomber.
The B-32, only other very heavy bomber produced during the war, had been viewed essentially as insurance against failure of the B-29.63 The first two XB-32’s were shaped in no small part by Consolidated’s experience with the B-24; like it, both were twin-tailed. Flight tests, beginning in September 1942, having revealed aerodynamic difficulties calling for redesign, the third experimental model was a single-tail plane. It performed more satisfactorily, and the AAF during 1943 and 1944 placed production orders for just under 2,000 of the aircraft.64 In other words, the decision was to gamble on the hope of the plane’s continued development, a natural decision in view of continuing uncertainties regarding the B-29 and of the advantage, in any case, of having two planes instead of one.65
Unhappily, the development of the B-32 lagged far behind that of the B-29. Not until August 1944 did the AAF put its first B-32 to service tests.* Not counting the three experimental models, only 13 B-32’s had been accepted by the end of 1944; total production by the end of August 1945 had reached 118.66 Only fifteen of these planes saw combat, in the western Pacific with the Far East Air Forces just at the close of the war.
The ultimate failure of the B-32 had been predicted by the NACA in 1942, to the great resentment of officials of the Consolidated Aircraft Corporation.67 Nevertheless, the hope persisted at AAF Headquarters into the fall of 1944 that the plane had “nothing basically wrong which cannot be fixed.”68 By late 1944, however, the operational
* See Vol. V, p. [.usaaf05 332].
experience of the Twentieth Air Force had removed all doubts as to the worthiness of its Superfortresses, and Arnold’s A-3 advised in December that a need no longer existed for the B-32 “as insurance against failure of the B-29.”.69 In February 1945 the Acting Chief of Air Staff, Brig. Gen. Patrick W. Timberlake, added the opinion that the “B-32 in its present form is not an acceptable bomber.” He cited two outstanding unsatisfactory features: the inability of the bombardier to see properly during the bomb run and the weight of the plane.70 By summer it had been decided to limit production to a total of 214, of which 40 were to be used for training and the remainder for a variety of projects, including the equipment of one combat group in the Pacific. In October 1945 the AAF terminated its B-32 contracts and directed that all B-32 planes be declared excess and disposed of.71 The moral perhaps is simply this: in heavy bomber development, where engineers necessarily work on the frontiers of experience and knowledge, success is achieved only at the cost of some failures. And those who in the hour of national emergency provided the B-17, the B-24, and the B-29 need offer no apologies for the B-15, the B-19, or the B-32.
Fighters
The chief fighter* planes used by the AAF during World War II were the P-38, P-39, P-40, P-47, and P-51. In the earlier part of the war two groups in ETO were equipped with the British Spitfire,† and in the last year of hostilities the P-61, a night fighter, became a familiar item of AAF equipment. One other plane, the P-63, was manufactured in quantity,‡ but it was never used as a first-line combat plane and most of the output was sent to the U.S.S.R. on lend-lease.
During the 1930’s the Air Corps fell behind other nations in the development of fighter-type aircraft. This lag is explained in no all part by a primary interest in the long-range bomber. Not only did that interest hold first claim on limited funds, but progress in the development of larger bombardment planes affected assumptions governing plans for fighter aircraft. The bombers built in the 1930’s
* After May 1942 this was the official designation for planes variously designated theretofore as pursuit, interceptor, or fighter.
† See Vol I, p. [.usaaf01 642]; Vol. II, p. [.usaaf02 230].
‡ The AAF accepted 3,273 P-63’s before the end of the war, but its peak inventory, in August 1944, for this plane was only 339.
flew at speeds equal to or even in excess of those achieved by contemporary pursuit models, and this fact, as GHQ Air Force explained early in 1940, “advanced the thought that airplane design had reached the point where a large airplane could be made to go as fast as a small one and that the defensive armament of the large plane was more than a match for the small plane.”.72 From this line of reasoning may be traced one of the major blunders of the AAF – its failure to provide in advance for the need of escort fighters in its heavy bomber operations. The big bomber, it was assumed, could. take care of itself, and thus no need even existed for developing a fighter of sufficient range to serve as an escort plane. Conversely, the proponents of the self-defending big bombers argued that the role of the fighter as an interceptor would decline, an argument which may help to explain another glaring deficiency of the war years – the lack of an effective night fighter, whose job is basically that of interception, until late in the war. How far the point should be pressed is debatable, but there can be no doubt that Air Corps doctrine in prewar years assumed “the ascendancy of bombardment over pursuit” and that this assumption hindered the development of pursuit aircraft.73
At the opening of hostilities, pursuit units of the Air Corps depended chiefly upon two planes, the P-39 (Airacobra) and the P-40 (Warhawk).* Both of them were approaching obsolescence despite the fact that they had been in production for not more than eighteen months on 7 December 1941.74 Especially disappointing was the P-39, whose low ceiling, slow rate of climb, and relative lack of maneuver-ability put its pilots at a decided disadvantage wherever they fought.† The P-40 proved to be a much better plane. Though a slow climber, given time it could reach altitudes permitting superior skill and tactics to offset the advantages of the enemy. The record set with the P-40 by more than one commander, but especially Chennault in China, was very creditable, but as other planes became available a continuing equipment of P-40’s was an unfailing mark of low priority. That the plane’s record owed much to the fact of its employment chiefly against the Japanese rather than the German Air Force is indisputable.
In 1936 and 1937, the years in which the P-39 and the P-40 had
* The two planes constituted more than half of all AAF fighters until July 1943, and prior to September of that year more than half of all those committed overseas. By August 1944 all P-39 groups had been converted and in July 1945 only one P-40 group remained in operation.
† See Vols. I, II, and IV, passim, but especially IV, pp. [.usaaf04 24], [.usaaf04 41-42], [.usaaf04 262-63].
been designed, the job indicated for them by national policy was one of coastal defense and of support for ground combat.75 And for those jobs the planes were not badly designed. No potential enemy promised to put high-level bombers over our coasts, and against an amphibious assault the rugged qualities of the two planes at low levels should have made them most useful in beating off the assaulting forces. In low-level strafing and bombing, the P-39 and P-40 repeatedly showed their worth during the war; as Kenney reported from the Southwest Pacific, each of the planes could “slug it out, absorb gunfire and fly home.”76
The Bell P-39 and the Curtiss P-40 were both single-engine mono-planes. The P-40 was slightly larger in dimensions, but the airframe weights of the later models of the two planes were about the same – approximately 4,000 pounds – and the combat weights were identical. The P-39 was unique in having its Allison V-1710 engine mounted behind the pilot’s cockpit instead of in the nose of the plane, a feature some pilots regarded as making the plane more vulnerable. A 37-mm. gun mounted in the nose fired through the hollow driveshaft. By contrast with the radical design of the P-39, the P-40 was essentially a further development of the P-36. The P-40 gained greatly improved performance by installation of a liquid-cooled Allison V-1710 engine in place of the P-36’s air-cooled R-1830 engine.77 Like other combat planes used during World War II, the P-39 and the P-40 increased in weight. The later models of the P-39, beginning with the D, had an airframe weight almost 50 per cent greater than that of the XP-39 and the increase in combat weight was almost as great. The increase in airframe weight of the P-40 ranged up to 10 per cent, but the increase in combat weight was almost 20 per cent. These changes resulted chiefly from the installation of armament, armor, and additional equipment. The P-39, starring with two .30-caliber and two .50-caliber machine guns and one 37-mm. gun, had two .50-caliber guns added to later models. The original P-40 carried only two machine guns, but most combat models carried six .50-caliber machine guns.78
The P-39D, first Airacobra produced in quantity, had a maximum speed of 368 miles per hour at an altitude of 13,800 feet. Later models showed no real improvement, though the increased horsepower of their engines did compensate for the increased weight. The story is much the same with the P-40, which held to a standard of 350 miles per hour at an altitude of 15,000 feet. Climbing speed tended to fall
as weight was added, and the ceiling remained low. Both the P-39 and the P-40 were credited with service ceilings, ranging throughout the various models, from 31,000 up to 38,000 feet; in practice, they rarely, if ever, reached these ceilings, certainly not in combat. The Allison V-1710 engine used in the planes had a critical altitude* of about 12,000 feet and lost power at higher altitudes. Combat at altitudes above 15,000 feet was rarely attempted.79 The over-all limitations of the two planes were such that the addition of superchargers seemed inadvisable in view of the promise that superior planes could be substituted.†
The first of these superior planes to make its appearance was the Lockheed P-38 (Lightning) – a high-flying twin-engine fighter of outstanding qualities. Designed in 1937 for high-altitude interception, the plane was Lockheed’s first venture into military production. Air Corps tests of the experimental model began in January 1939, just as the Presidential program was giving a new impetus to all plans for aircraft production. In April an order for thirteen service-test models was placed; in September a production order for sixty-six planes was negotiated. A second order, this time for 607 planes, followed in August 1940, despite the fact that the first service-test model was yet to be delivered. Production continued to lag: delivery of the 13 planes first ordered was not completed until June 1941; total deliveries reached only 39 by the middle of August; and, while acceptances in November went up sharply to 74 planes, the AAF inventory on the eve of Pearl Harbor showed no more than 69 P-38’s.‡ For these delays, the AAF was inclined to blame Lockheed, and suspicion existed that the company preferred to concentrate on its own commercial Lodestar and on British orders for the Hudson.80 Whatever the fact, the delay was costly.
This plane, whose second engine proved a comforting feature to its pilots, achieved a top speed ranging upward from 390 to 414 miles
* Critical altitude is altitude at which the greatest speed is attained by the airplane in level flight using military rated power and with all design gross weight items installed.
† Between 1940 and 1944, when acceptances ended, a total of 9,558 P-39’s and 13,738 P-40’s were accepted. Peak AAF inventories show 2,150 P-39’s in February 1944 and 2,499 P-40’s in April of that same year. As these figures suggest, the greater number accepted were eventually shipped to our Allies, among whom the Russians valued especially the P-39 for its effectiveness in low-level support of ground troops.
‡ It should be noted, however, that there was usually a time lag between acceptance of a plane and its appearance in inventories.
per hour. Its rate of climb gave the pilot an even chance and its range was such as to encourage the AAF to experiment in 1942 with flying P-38 units to their station in England.* As a fighter-bomber with a bomb load of 2,000 pounds, the plane had an average combat range of 600 to 700 miles. On escort duty, with no bombs and a maximum fuel load, later models approached a range of 2,000 miles, though for practical purposes 1,500 miles was about the limit. In ferrying, the reach might be 2,500 miles.81 The two V-1710 engines of models J and L each generated 1,450 take-off horsepower, thus providing a power unit equal to the plane’s size, which at the start was double that of the P-39 or the P-40. The usual armament of four .50-caliber machine guns and one 20-mm. gun was supplemented as needed by an external bomb capacity reaching 3,200 pounds. Fuel capacity was expanded from the 310 gallons of the earlier models to a remarkable 1,010 in the later series. The P-38 was the first fighter to be equipped with turbo-superchargers, permitting operation at greater speed at high altitude.82
It was also the first AAF fighter that could in any way be compared with the Messerschmitt 109 or the British Spitfire.† Seeing service in all theaters, the plane effectively performed the varied functions of a fighter and in a modified version proved especially useful for photo reconnaissance. By the spring of 1944 there were thirteen P-38 groups overseas. Total acceptances from the factory reached 9,536 at the end of August 1945. Peak production had been reached in August 1944. The highest point of inventory came in March 1945.83
The AAF had come by the end of the war to depend still more heavily upon Republic’s P-47 (Thunderbolt). In fact, after January 1944 groups equipped with P-47’s represented better than 40 per cent of all AAF fighter groups serving overseas; after March of that year inventories never showed less than 5,000 of the planes on hand. The top listing in May 1945 was 5,595. At summer’s end in 1944 the AAF had 31 P-47 groups, a total which reflected the rapid rise in production from 532 planes in 1942 to 4,428 in 1943 and over 7,000 in 1944.†84
* See Vol I, pp. [.usaaf01 641-45].
† The Me-109G had a maximum speed of 400 miles per hour at altitude and a range of over 600 miles. The Spitfire IX had a maximum speed of 406 miles at altitude and a range of 425 miles.
† 3,559 were added before August 1945. Republic produced all P-47’s except for 354 by Curtiss-Wright.
The Thunderbolt had been designed in 1940, at a time when the Air Corps had become fully alerted to the need for a plane that would compare with the best European models. The original experimental model was powered by a liquid-cooled engine, but there were doubts in 1940 that engine production could keep up with the demands of a program depending upon liquid-cooled engines for all Air Corps fighters. Accordingly, it was decided to switch to a new Pratt & Whitney R-2800 air-cooled engine, even though this called for redesign of the plane and a consequent delay in its production.85 The XP-47B with its air-cooled engine first flew in May 1941; the first production article was not accepted until the following December. Meanwhile, testimony of the high hopes entertained for the plane was given by employment of such leading Air Corps pilots as Col. Ira C. Eaker in its test-flights.86 For a time it was hoped that the plane could benefit from combat-testing by making the P-47 available to the RAF in the Middle East. But technical difficulties affecting production plans led Arnold in September 1941 to notify the British that it would be inadvisable to try the plane in combat until “teething troubles” with “a combination of a new airplane, a new engine and a new supercharger” had been overcome. At that time an overoptimistic estimate set May 1942 as the earliest date on which the plane might be ready;87 actually, the AAF found it impossible to get the P-47 into combat before April 1943.* Production had begun to move in the preceding spring. The first P-47 group was equipped in November 1942 and in January reached England, where two more months were required to straighten out difficulties with the engine and with communications equipment. Thereafter, the P-47 came fast.
It was a powerful plane. Its engine with more than 2,000 horsepower put the P-47 ahead in this category of all single-engine fighters of the AAF and gave it rank with any other contemporary single-engine fighter in the world. With its superchargers, the plane climbed fast and performed admirably at high altitude. Its stubby appearance bespoke a ruggedness exceeding that of any other AAF fighter, and no plane of the war proved itself more versatile. With a powerful armament of six to eight .50-caliber machine guns and the additional capacity for six 5-inch rockets with a 2,000-pound bomb load, or for ten rockets without bombs, the P-47 proved that the fighter-bomber provided the best answer to the long quest for an outstanding attack
* See Vol. II, p. [.usaaf04 335]
plane.88 Though employed with satisfaction in all major theaters, the Thunderbolt probably deserves to be remembered chiefly for its work in the Ninth Air Force as a fighter-bomber following the invasion of western Europe in 1944.* It had no peer as an escort plane except for the P-51. The original fuel capacity of a little over 300 gallons severely restricted its radius of action, but the addition of belly and wing tanks brought the full load in the P-47N up to 1,266 gallons for ferrying purposes. Combat fuel loading usually ranged from 300 to 600 or 700 gallons, depending on the need. Beginning in 1943 with a combat range of about 500 miles as a fighter-bomber and 1,000 miles as an escort fighter, the P-47 in its later models extended the figures to 800 and 2,000 miles. Top speed, meanwhile, had increased from some 425 miles per hour to 460. The rate of climb below 25,000 feet fell off as a result of increased combat weight, model N weighing 3,000 pounds more than D, the first series in large production.89
The story of the P-51 came close to representing the costliest mistake made by the AAF in World War II. By 1943 it was becoming all too clear that the big bombers would require the protection of full fighter escort if an effective campaign of strategic bombardment against Germany was to be maintained at Prewar assumptions as to the “ascendancy of bombardment over pursuit” long since had been dropped, but understandably there continued to prevail an opinion which had been formally expressed in 1940 in these terms: “no fighter plane can be designed to escort heavy and medium bombardment to their extreme tactical radius of action and there engage in offensive combat with enemy interceptor fighter types on equal terms.” The escort plane, it was concluded, “in order to have the range and speed of the aircraft it accompanies, may be as large and at least as expensive as such aircraft.”90 In 1941, when plans for the giant B-36 were under discussion, it was suggested that an escort of comparable size might have to be provided,91 and AWPD/ 1, the AAF’s basic war plan of that same year, recommended for solution of the more immediate problem a plane that was essentially a modified bomber. As the Eighth Air Force began its bombing operations in August 1942, a special board headed by Brig. Gen. Alfred J. Lyon recommended modification
* See especially Vol. III, [#usaaf03 chapter07 Chapter 7 and chapter08 Chapter 8.
† For this story, with notice of the early correction of prewar assumptions regarding the capacity of the big bomber to take care of itself, see Vol. II, passim, but especially pp. 229-31, 267-68, 334-37.
of the B-17 and B-24 to provide needed “destroyer escort planes.”* This led to an unsuccessful experiment by the Eighth Air Force in 1943 with the YB-40, a modified B-17 sent over in the hope that it might meet the growing need for long-range escort.†
Meanwhile, the answer lay in two developments which in origin were unrelated to the search for an escort plane. The great distances over which planes had to be delivered to widely scattered combat zones, together with a critical shortage of shipping for the purpose, had forced the AAF in 1942 to give close attention to possibilities for extending the range of its planes to a point that would permit the ferrying of as many of them as possible to their combat stations. To this impulse there was quickly added the need for the longer range required to meet developing combat demands in the several theaters. As a result, by 1943, and in many different places within the AAF, experimentation was demonstrating possibilities for the extension of fighter ranges which surprised American, British, and enemy combat commanders alike.‡ The problem was largely one of increasing fuel capacities, and the most important of immediate aids to this end was found in the disposable fuel tank, a device known for many years and to which the AAF had given close attention since 1940.92 As the engineers concentrated on all aspects of the problem, increased range came to be the single most distinguishing feature in the development of AAF planes during World War II. And of all fighter types none had the potentiality displayed by the P-51, a plane which the AAF had been slow to appreciate.
It had been designed by North American for the British in 1940, as a substitute for the P-40’s asked for by the RAF. The P-51 had its genesis in improvements contemplated by the Air Corps for the P-40, and Curtiss turned over to North American useful technical data. But the Air Corps’ plans had come to depend on the P-38 and the P-47; accordingly, the Air Corps took only a limited interest in the P-51, stipulating that it be provided with two free articles in the event production for the British was attempted. Production got under way in the latter half of 1941 in accordance with relatively modest orders
* See Vol I, p. 604.
† See Vol. II, particularly pp. 268 and 680.
‡ This extension, though the impulse came from an interest in ferrying, proved to be of importance primarily to tactical operations. With the help of deck-loading, it was possible to send most fighters by ship.
from the British, who first put the plane to work in their Army Cooperation Command for ground support. The RAF was quick to recognize the Mustang as “the best American fighter that has so far reached this country,” and began to compare it favorably with the Spitfire, currently rated as the world’s best fighter.93 Our assistant military attaché in London, Maj. Thomas Hitchcock, reported to Washington in the fall of 1942 that the P-51 was “one of the best, if not the best, fighter airframe that has been developed in the war up to date.” Dropping into the vernacular of his interest as a famous horseman, he advised “development of the Mustang as a high altitude fighter” by “cross-breeding it with the Merlin 61 engine.”94 Others, including Eddie Rickenbacker and AM Sir Trafford Leigh-Mallory, confirmed Hitchcock’s report,95 and within a month Arnold could notify President Roosevelt that the Rolls Royce engine was being tested in the P-51 and that approximately 2,200 of the planes already had been ordered by the AAF.96
This was in November 1942, and the extensive changes attendant upon the substitution of a new engine held up production through the following winter.97 Not until November 1943 did the AAF get a P-51 group to the United Kingdom, and it flew its first long escort mission on 13 December – 490 miles to Kiel and back – which was the record to date. In the following March the Mustangs accompanied the heavies all the way to Berlin. Considering the late start, the production record was a remarkable one. By August 1944 the production rate had passed that of the P-47, and by the close of the war, a year later, the AAF inventory of the plane had reached the huge total of 5,541.98 The Eighth Air Force had converted all save one of its fighter groups to P-51’s, the P-47’s going to the Ninth Air Force; everywhere the strategic forces held first claim. Following the capture of Iwo Jima in February 1945, the Mustangs added to their already secure reputation as the world’s best escort by aiding the B-29’s in their mounting assault on Japanese targets.* After the war Arnold frankly admitted that it had been “the Air Force’s own fault” that this superior plane had not been employed earlier.99
A single-engine, low-wing monoplane, the P-51 was much lighter than either the P-38 or the P-47. Though the combat range of the original P-51, built to meet the short-distance needs of the RAF, had not exceeded 400 miles, it reached 1,800 miles with the P-51H, which
had a top speed of 487 miles per hour. Its service ceiling of better than 40,000 feet made it a truly high-altitude fighter. The plane normally carried six .50-caliber machine guns, and it could take rockets or bombs up to 2,000 pounds.100
The Northrop P-61 (the Black Widow), which saw service during the last year of the war, was the first American plane specifically designed for service as a night fighter, for which a need had been repeatedly felt from the early days of hostilities. Design had been begun by Northrop in November 1940 at the instigation of the Air Corps, and a formal contract for two experimental articles was signed in January 1941. Subsequently, orders were placed for more than 2,000 planes, but only 682 had been delivered by August 1945. The first XP-61, though test-flown on 26 May 1942, was not delivered to the AAF until July 1943; deliveries on production contracts began late in 1943. P-61 squadrons were in action with the Ninth Air Force in the European theater before D-day and appeared in the Mediterranean and Southwest Pacific theaters during the summer of 1944. The coal-black plane proved itself capable of a variety of night missions, operating as an intruder* as well as an interceptor.101 An attempt to modify a late model P-61 for use as a long-range day fighter was made in 1945, but the development was overtaken by the end of the war and subsequently dropped.102
The Black Widow was an all-metal monoplane with a twin fuselage and a twin tail, somewhat resembling the P-38 but much larger. It had two Pratt & Whitney R-2800 engines, each of which developed more than 2,000 horsepower. In size, the P-61 was more nearly comparable to the medium bombers than the fighters. Its wing span and length were greater than those of the A-20, and its combat weight of 28,000 pounds was at least 2,000 pounds more than that of the A-20. It was almost three times as heavy as the P-51 and almost twice as heavy as the P-47 at combat weight. Its internal fuel capacity of 640 gallons was supplemented by two or four wing tanks, each of which held 165 or 310 gallons of fuel. This gave some of the P-61’s a fuel capacity of 1,880 gallons – a capacity which was rarely, if ever, used. The original combat range of 700 to 800 miles went up to better than 1,000, and the ferrying range ultimately doubled that figure. Its armament consisted of four .50-caliber machine guns and four 20-mm.
* Intruder missions were usually night nuisance raids by single planes against enemy targets.
B-25 North American Mitchell
B-26 Martin Marauder
B-17 Boeing Flying Fortress
B-24 Consolidated Liberator
B-29 Boeing Superfortress
B-32 Consolidated Dominator
P-38 Lockheed Lightning
P-39 Bell Airacobra
P-40 Curtiss Warhawk
P-47 Republic Thunderbolt
P-51 North American Mustang
A-36 North American (Fighter-Bomber Version of Mustang)
C-47 Douglas Sky Train
C-47 Interior View
C-46 Curtiss Commando
C-54 Douglas Skymaster
L-4 Piper Grasshopper
L-5 Vultee Sentinel
XB-15 Boeing
P-82 North American Twin Mustang
P-59 Bell
P-80 Lockheed Shooting Star
B-36 Consolidated Vultee
guns, and some models were equipped to carry either 3,200 or 6,400 pounds of bombs externally. The most notable feature of the plane was the large quantity of radar and communications equipment it carried in order to permit effective night operation. The P-61 carried a three-man crew consisting of a pilot, radio operator, and gunner. Top speed remained at about 360 miles per hour and the maximum ceiling was over 30,000 feet. The plane proved to be highly maneuverable, more so than any other AAF fighter.103
Though dependent upon a bit of luck with the P-51, the AAF had three outstanding fighters, and of these two were for their respective tasks superb.
Reconnaissance and Liaison
In the early days of military aviation, reconnaissance, then known as observation, had been the prime mission of the Army’s air arm. The importance of reconnaissance, except in relation to other and rapidly developing potentials of the airplane, had suffered no decline in the years between the two world wars. Indeed, experience in the second war soon indicated that this old mission had acquired a growing significance as an intelligence service indispensable not only to other arms but also to the success of the AAF’s own special operations. The planning, execution, and assessment of air operations – and this was particularly true of strategic bombardment – depended most heavily on photo reconnaissance. The Air Corps, however, had developed no plane specifically designed for the performance of this function, and the AAF remained dependent throughout the war upon its standard combat models or modifications of them for the special purposes of reconnaissance. The one exception was found in the small, short-range planes employed for artillery spotting.104
In October 1943 the Hughes Aircraft Company undertook to produce a plane having the range, speed, and other requirements for a special reconnaissance-type plane. Designated the F-11, the aircraft was supposed to show a minimum range of 3,000 miles, a ceiling of 60,000 feet, and a speed of 400 miles per hour. These specifications were so high as to be considered by the Materiel Command as virtually impossible of attainment.105 But Arnold, yielding apparently to the insistence of Col. Elliott Roosevelt, one of the AAF’s most experienced photographic reconnaissance officers, decided to gamble on the F-11 despite the persistent objections from the Materiel Command
and the Air Staff. He later explained that nothing else was in sight and admitted that his “guess was wrong.”106 The first F-11 was not turned over to the AAF until well after the end of the war, and it did not measure up to specifications. Early in 1994 the AAF had got Republic going on a four-engine reconnaissance type, but it proved impossible to produce the plane before the end of the war, and the project was eventually dropped.107
Meanwhile, the more adaptable of the combat planes had been converted for reconnaissance purposes.* Of these the P-38 served chiefly, AAF inventories at the beginning of summer in 1945 showing something over 800 of the F-4 and F-5 out of the approximately 2,000 photo-types on hand. The P-51, as the F-6, did good work in Europe. Only the B-29, as the F-13, had the necessary reach for aid to strategic operations in the Pacific. Satisfactory over-all figures are difficult to get, for the modification, which represented chiefly adjustments for different equipment, was often made in the theater on standard models. Efforts to procure the celebrated British Mosquito bomber for adaptation proved disappointing.108
Provision for the Army’s need of observation planes presented a different problem. During World War I, though distinctions of function affected the design of military aircraft, most standard models had capacities sufficiently limited to allow diverse employment of them. But by the second war the standard planes of the AAF were of a size that did not permit landing on any strip, and they operated at speeds which gave them little utility for the type of service required for such tasks as artillery spotting. The need was for a small and highly maneuverable plane that could operate under almost any weather and airfield conditions.
Despite prodding by the General Staff, the Air Corps had failed to produce a satisfactory liaison plane (the designation adopted in 1941), a failure attributable in part to the continuing conviction that a small, slow, unarmed plane could not survive in the battle area. Success with small commercial-type aircraft in the maneuvers of 1941 confirmed the Army in another and, as events proved, correct opinion. By January
* The photographic planes and their combat equivalents were:
| F-3 | A-20 |
| F-4 | P-38 |
| F-5 | P-38 |
| F-6 | P-51 |
| F-7 | B-24 |
| F-8 | Mosquito |
| F-9 | B-17 |
| F-10 | B-25 |
| F-13 | B-29 |
1942 the AAF had been given responsibility for providing almost 4,000 “puddle jumpers” for the Army. The job was not well handled; only the fact that large-scale ground operations were delayed until 1944 and 1945 kept the supply within reach of the great demand created by the needs of the Army, as well as the Civil Air Patrol, the Civilian Pilot Training Program, and the Office of Strategic Services. The AAF itself also planned to use this type of plane in large numbers for miscellaneous purposes, such as liaison between bases. The several interested parties at times worked at cross-purposes, and requirements were subject to many changes. To put it briefly, there was much confusion.109 Eventually, two first-class models emerged: the L-4 (Piper Cub) and the L-5 (Stinson), both adaptations of commercial types. Assigned to divisions, corps, and armies, they performed a wide variety of functions, which included observation, artillery adjustment, aerial evacuation, column control on the march, wire laying for communications, camouflage checking, liaison, and courier work. The AAF accepted a total of 5,611 L-4’s and L-14’s (improved version of the L-4), and 3,590 L-5’s, which together constituted more than 65 per cent of the 13,558 liaison-type planes accepted between June 1940 and August 1945. The peak inventory was 4,211 of these planes in June 1944.110
Transport and Troop Carrier
The AAF was hardly more successful in producing specialized aircraft for its rapidly growing air transport service than it had been in developing a photo reconnaissance or a liaison plane. As in the case of the liaison plane, it had to adapt already proved commercial transports to military use, and as with the photographic plane, it became necessary to modify combat aircraft, bombers specifically, for transport purposes. There was little debate as to what was desired: some plane equally useful for the delivery of either cargo or troops to their destination; but the only plane specifically developed for this purpose during World War II, the C-82, did not actually see service until after the war.111 Meantime, great resourcefulness was displayed in meeting emergency demands on wholly unanticipated scales with the equipment that could be made available. The planes which formed the backbone of the AAF’s transport fleets were the C-47, C-46, and C-54.
The Douglas C-47 (Skytrain) was a military cargo version of the
DC-3, stand-by of the commercial airlines for a number of years before Pearl Harbor. With other modifications the DC-3 became the C-53, a troop and hospital transport. A steady and proved aircraft, the C-47 earned for itself a reputation hardly eclipsed even by the more glamorous of the combat planes. The work horse of the air, one found it everywhere, and everywhere, whether shuttling freight or airborne troops, it did the job dependably. Before the war was over the AAF had accepted more than 10,000 DC-3 type planes, which was nearly half the transport planes it received between 1940 and 1945.112 In troop carrier units the C-47 usually carried a four- or five-man crew.
The Curtiss-Wright C-46 (Commando) was the military version of an as yet unproved commercial transport. Like the C-47, it was a twin-engine monoplane but much larger and heavier, with a maximum cargo capacity of 15,000 pounds against 10,000 for the C-47, and a passenger load capacity of 12,000 pounds against 6,500 for the C-47. Accordingly, the AAF rested high hopes on its development, but engineering difficulties so persisted that it did not get extensive use before 1944. Total acceptances reached only 3,144 by August 1945.113
The Douglas C-54 (Skymaster) became the outstanding four-engine transport of the war. Known in its commercial model as the DC-4, the C-54 served chiefly on the long-distance hauls of ATC. Strictly a transport and cargo plane, which was not modified for troop carrier purposes, and would have been uneconomical in such a service, the C-54 was not available in large numbers until 1944.* Its most colorful achievement came no doubt on the “Hump” route to China, but it also cut down the great distances separating the United States from many other far-flung battle fronts.114
Among the bombers modified for transport service, first choice fell on the B-24, because of its range. Designated the C-87, the modified bomber performed important transport services for the AAF from the beginning to the end of the war. As the C-109, it was used as a tanker and hauled large quantities of fuel across the Himalayas from India to China.115 Many unmodified B-24’s saw unanticipated service as transports and tankers in theaters throughout the world, a notable example being the use of a wing of Eighth Air Force B-24’s in September 1944 to haul gasoline for Patton’s Third Army in France.
A variety of light utility aircraft carried the conventional symbol of the cargo plane, though the cargo carried was rarely heavier than
* The AAF accepted more than 1,000 C-54’s before the war ended.
the baggage of some inspector or staff officer on a hurried mission. The need for such carriers during the early days of AAF expansion was met by the purchase of a wide variety of light commercial planes, which soon presented peculiar and serious problems of maintenance. In time, four planes in this class were acquired in quantity: the Fairchild C-61, a single-engine four-passenger transport; the Cessna C-78, a twin-engine transport version of the AT-17 trainer which could carry five passengers with baggage; the C-64, a single-engine plane designed as a “float and ski” freighter which was produced by Noorduyn Aviation Limited of Montreal and was used chiefly in arctic regions; and finally, and most satisfactory of all, the Beech twin-engine C-45. Its production was retarded because of the higher priority given to training planes, but the AAF eventually accepted 1,771 C-45’s by the end of the war.116 The importance of the transport plane to the operations of the AAF, whether as a carrier, troop transport, or long-range cargo carrier, is illustrated by the growing inventory of these planes. In July 1939 the AAF had only 118 transports, and on the eve of Pearl Harbor it had only 216. Thereafter the inventory rose steadily; by August 1944 the AAF had more than 10,000 transports on hand.
The glider was an important auxiliary of the troop carrier version of the transport plane. The Army had paid little attention to this sports craft until the Germans demonstrated in 1940–41 its utility for military operations. The Materiel Division began study of the engineering aspects of the glider in February 1941, and initiated procurement of gliders for training purposes in April 1941. Two months later, a design competition for cargo- and troop-carrying gliders was held, from which the Waco fifteen-place CG-4A emerged as the most satisfactory. Its procurement was undertaken early in 1942, and the whole glider program was steadily expanded as airborne operations grew in size and importance.117 Although the CG-4A was frequently criticized after it appeared in the fall of 1942, it proved itself in airborne operations in Europe and Burma, where it was towed by C-47’s or C-53’s, and none of the other gliders developed during the war could be seriously considered as a replacement for it. It was made of wood, had no motor or armament, and carried one radio for communications. More than a dozen companies participated in its production, since the program – which included virtually all of the 15,000 procured – was too large for the Waco Company to handle alone.
Trainers
Almost 25 per cent of the grand total of planes accepted by the AAF through August 1945 were trainers – all told some 55,000 of them.118 In contrast to the combat planes, their several qualities became little known to the American public, but their production necessarily held the highest priority during the earlier years of the AAF’s extraordinary expansion. The peak of production was reached long before that of the combat types, and from November 1940 through February 1943 trainers constituted at any time more than 50 per cent of the total inventory of AAF planes. As the training commands cut back their programs in 1944, the percentage moved downward.119 The primary trainer was a small, light plane designed for initial training in flight; the basic served in an intermediate stage to introduce the cadets to service-type planes; the advanced trainer served in the final stage of individual flight training to provide experience with planes of size and performance more nearly that of the combat models. Normally the combat model was introduced at the level of unit training.* But the regular AT planes were at times supplemented by old and obsolete models of combat aircraft employed for advanced training.120 The complexity and high performance qualities of World War II combat models left no choice but observance of these successive stages in the training of aircrews.
Most of the training aircraft used were versions of commercial types standardized to permit uniform training methods and to reduce problems of maintenance. Even the advanced trainers were usually commercial models adapted for training purposes. The most important of the AAF’s primary trainers during World War II were the Stearman PT-13, with its offspring, the PT-17 and -27; and the Fairchild PT-19 with its two variations – the PT-23 and -26. The PT-13, a wood, metal, and fabric biplane, though first acquired by the Air Corps in 1936, was still regarded by the Training Command at the end of the war as the “best primary training” airplane ever developed. The PT-19 was developed before the war to meet the Air Corps’ requirement for a monoplane PT. The Vultee BT-13 and BT-15, which differed only in their engines, served almost exclusively as the basic trainers throughout the war. The outstanding advanced trainer was the North American AT-6, a single-engine, all-metal, low-wing monoplane,
* See below, pp. 567 , 600 ff.
known in the United States as the Texas and in Canada and the United Kingdom as the Harvard. The Beech Aircraft Corporation developed the AT-7, -10, and -11 series of twin-engine advanced trainers, all of which were variations of the C-45. The AT-7 was used for navigation training and was an all-metal, low-wing monoplane. The AT-10 was the same plane constructed chiefly of wood and fabric and equipped with different engines, but it was not as satisfactory as the AT-7. The AT-11, equipped with guns and bomb racks, was used as a bombardment trainer. Other advanced trainers procured in smaller quantities were the Cessna AT-8 and AT-17, both twin-engine planes.