Chapter 9: Smoke
At Algiers, Bizerte, Naples, and other Mediterranean cities during World War II German bombers flew over harbors intent on blowing Allied shipping out of the water. In all but a relatively few instances they found nothing but an impenetrable haze covering the targets. On New Guinea and Luzon American paratroopers dropped safely to earth protected from bullets of Japanese riflemen by screens of white smoke. At beachheads, highways, and river crossings in Italy, France, and Germany, troops and trucks went about their work under a shield of artificial fog. Never before had armies been able to protect their troops and hide their movements as successfully as Allied forces did in World War II.
Military history records the tactical use of smoke in early times, but reliable smoke munitions are of fairly recent origin. Not until World War I did armies develop standard munitions and give them a wide trial. The British Army produced grenades and shells containing white phosphorus that emitted white smoke, and carbonaceous mixtures that gave off black smoke. The German Army, lacking phosphorus, depended on oleum, chlorosulfonic acid, and sulphur trioxide, all of which reacted with moisture in the air to form white fog. The French contributed Berger mixture, which threw off a gray smoke when heated. The American Army designed grenades, shells, candles, pots, and other munitions based on European originals, but did not get them to the battle zone in time for use. From the smoke munitions of World War I evolved most of the efficient screening devices used by friend and foe in World War II.
White Phosphorus
White phosphorus (CWS symbol, WP) is a soft waxy substance that reacts spontaneously with oxygen. When phosphorus is scattered from a bursting munition the heat of the explosion causes the phosphorus to
Smoke pots being set off in the Argonne forest, near Beaucamp, Meuse, France, October 1918.
ignite as soon as exposed to air and throw off a dense white smoke of phosphorus pentoxide. The material WP was unsurpassed as a smoke producer and it also paid dividends in other ways. Burning phosphorus wounded enemy soldiers just as readily as rifle bullets and shell fragments. Fragments of burning phosphorus streaking through the air were also hard on enemy morale. For these reasons the CWS purchased two hundred million pounds of WP from 1942 to 1945, far more than any other smoke agent obtained during the war.1
The CWS used white phosphorus as a filling for shells, rockets, bombs, and grenades, all of which the armed forces employed extensively in World War II. Artillery and chemical mortar companies hurled shells to set fire to enemy held buildings and cane fields, to drive enemy soldiers from fortified positions, to unnerve enemy troops, to support infantry attacks, and to shield flame thrower operators. Naval vessels threw WP at shore installations on Saipan, Eniwetok, and other places to support amphibious assaults. The Army fired a sizable portion of the two and one-half million 2.36-inch rockets filled during the war to screen operations, to start fires, and to wound and unnerve the enemy. Airplanes dropped WP bombs on enemy installations to start fires or aid infantry. For infantrymen and
marines, the CWS filled more than five million hand grenades and two million rifle grenades with WP, and, as indicated earlier, the American phosphorus was considered by the Germans, who were in a good position to know, of superior quality.2
Despite its excellence as a smoke agent, WP had a fault that brought objections from the field early in World War II. The smoke had a tendency in still air to rise into a pillar instead of lingering close to the ground where infantrymen wanted it. Pillaring depended primarily on the size of phosphorus fragments. If the bursting charge of a munition shattered the solid phosphorus filling into extremely fine particles, a large reactive surface area was exposed to the air. The large surface allowed the phosphorus to burn rapidly and in so doing give off a considerable quantity of heat which billowed the smoke upward. If, on the other hand, the explosion broke the phosphorus into a few large fragments, the exposed area was not nearly so great. The phosphorus then burned more slowly, emitted less heat, and the smoke hovered close to the ground.
The CWS tried various expedients to keep the explosion from completely shattering the phosphorus. In one experiment engineers stuffed wads of steel wool into a phosphorous shell to see if the network of steel threads would hold the phosphorus in chunks. In other tests they poured melted phosphorus into metal and paper tubes, and packed these tubes inside shells. None of the experimental shells was entirely successful and the problem remained unsolved until 1944 when the NDRC Munitions Development Laboratory at the University of Illinois devised a new filling consisting of small granules of phosphorus, about the size of grains of sand, suspended in a matrix of rubber. Explosion broke this filling, called plasticized white phosphorus, PWP, into chunks several millimeters in diameter that burned slowly for several minutes. Munitions loaded with PWP raised a better smoke screen than ordinary phosphorus munitions. Furthermore, the phosphorus, being in large pieces, was more effective against enemy troops. Although PWP was not completely satisfactory, since the phosphorus slowly separated from rubber in storage during hot weather, it was the best solution devised during the war.3
The CWS produced a few hundred experimental 75-mm., 105-mm., and 155-mm. PWP shells in late 1944. The following year plants got into production and turned out 891,941 pounds of PWP. The service loaded this into mortar shells, recoilless mortar shells, bombs, and 3.5-inch and 4.5-inch rockets, but these appeared when the curtain was falling on the last act of the war and they were practically unknown to the fighting man.4
In contrast to the Americans and the British, the Germans did not have phosphorus ammunition. Germany lacked the raw materials for producing phosphorus, and its Army had to depend on less effective Berger mixture, described below, and on oleum. Grenades and smoke pots generally took a Berger-type filling, while mortar smoke ammunition, artillery smoke ammunition, and smoke rockets contained pumice saturated with oleum. The Japanese had a wide range of WP bombs, mortar shells, artillery shells, and grenades, but they used WP much less than the Americans did.5
Smoke Pots
Along with the first wide-scale use of white phosphorus as a smoke producer, World War I saw the invention of a new type of smoke agent, Berger mixture, by Capt. Ernest E. F. Berger of the French Army. The mixture, containing carbon tetrachloride, powdered zinc, and zinc oxide, was inert at normal temperatures, but when it was heated the ingredients reacted and gave off a dense gray smoke of carbon and zinc chloride particles.6
In the United States CWS chemists experimented with Berger mixture during the 1920s and 1930s and replaced carbon tetrachloride, a liquid, with hexachloroethane, a solid, to decrease evaporation during storage. (From the name hexachloroethane came the symbol HC employed by the American Army in designating this type of smoke agent.) By 1940 the service was using Type A HC containing hexachloroethane, zinc, ammonium chloride, and ammonium or potassium perchlorate, as a filling for smoke pots and other munitions. The fall of France cut off America’s supply of imported perchlorate, and chemists began to search for substitutes. They chose calcium silicide, which Captain Berger had suggested
Smoke screen demonstration over the harbor, Palermo, Sicily. The screen was produced by mechanical smoke generators and smoke pots in thirteen minutes.
back in World War I and which the British Army had adopted. The new mixture, designated as Type B HC, functioned satisfactorily but industrial firms had trouble producing it. They found that calcium silicide could be a dangerous material. When it was ground to a powder it reacted rapidly with oxygen in the air sometimes causing an explosion. Plants redesigned their equipment and took great precautions, but the danger led chemists to develop a safer mixture, Type C, containing grained aluminum, hexachloroethane, and zinc oxide. Then came the threat of a shortage of hexachloroethane. Chemists had to develop a substitute mix, Type E, with carbon tetrachloride replacing hexachloroethane. Actually the shortage of hexachloroethane never matured and the CWS was able to procure all the Type C mix it wanted. Engineers discovered that the new Type E mix could be loaded into bombs more easily than the other types, however, and the CWS used it extensively as a filling for M77 ten-pound bombs.7
With types A, B, C, and E HC mixtures, the CWS had a range of smoke agents suitable for hand grenades, rifle grenades, artillery shells, rockets, bombs, and smoke pots. Shells, grenades, and bombs found employment during the war but by far the most widely used HC munition was the smoke pot.
At the time of Pearl Harbor the CWS’s standard smoke pot, M1, was a cylindrical can 8 inches high and 5 inches in diameter, holding about 10 pounds of HC. Fired by hand or electric current, it released a cloud of grayish white smoke for a period of 5 to 8 minutes. The service had devised this pot in the early 1930s as a munition for training exercises, but when war came it was the only munition of its type available and the American Army took it along to North Africa.8
Because they released smoke immediately, pots were useful in setting up a preliminary screen during the five or so minutes that it took large mechanical generators to warm up and start functioning. They helped shield harbors and installations on the coast of North Africa as well as at the harbors at Palermo, Licata, and Porto Empedocle on Sicily.9
Before the landings on Italy, troops employed smoke almost exclusively for harbor defense and only to a minor degree in amphibious operations. But at Salerno, where the enemy kept beaches under observation for two weeks, the Army used smoke along the shore to protect incoming landing craft from enemy bombers, machine guns, and artillery fire. The small size and light weight of pots enabled troops to carry them ashore and employ them until heavy, bulky, mechanical generators could be landed. After Salerno, smoking of invasion areas by army units and by naval support boats became a standard practice on the coast of Europe and on Pacific islands.10
In Italy pots also graduated from harbor defense and invasion defense to forward area defense. Troops employed them to screen supply routes, bridge construction, river assault crossings, tanks, ammunition dumps, troop concentrations, ground operations, and even to hide mortar flash. As a result of the wide usage of pots under many conditions, the CWS learned of minor flaws in the design of the munition. Those that were opened in anticipation of combat could not be resealed tightly. Moisture from the air crept under the lid, disintegrated the matchhead and rendered
small M1 smoke pots set off in a series to maintain a screen for troops in the Gothic Line, Italy.
the pots useless. Furthermore, handles protruding above the lids made it impossible to stack the pots. To overcome these defects engineers substituted a flat screw-type lid without handles that could be resealed, and allow pots to be placed one on the other. The revised model bore the designation M1A1.11
In addition to these flaws, smoke pots at times proved to be smaller than troops desired. More men were required for maintaining a smoke screen with small pots than with large ones. In 1944 the CWS began to turn out pots holding three times as much HC, and burning twice as long. Almost a million large pots, designated as model M5, came from filling lines before the war ended. They did not reach Europe in appreciable quantities before V-E Day, and the original M1, of which more than five million were produced, remained the workhorse of ground troops.12
Although HC was regarded as nontoxic as the other CWS screening agents (titanium tetrachloride, chlorosulfonic acid-sulphur trioxide, and white phosphorus), its use in troop training exercises showed that when breathed in a confined area it might produce fatalities through extreme lung irritation. The airborne particles of zinc chloride that were dispersed during the burning of HC were believed to be the only toxic element, until further tests revealed that hexachloroethane mixtures contaminated with ammonium chloride were even more lethal. Wearing the gas mask in HC smoke clouds provided adequate protection, and the Army changed manuals and other training literature accordingly.13
The German Army did not have as large a variety of HC-type smoke munitions as did American forces. Smoke bombs, grenades, and candles (analogous to U.S. pots) made up the list, and of these the infantrymen depended generally on the candle. Type 39 candle, a metal cylinder slightly over 5 inches in height and 3 inches in diameter, held sufficient HC-type mixture to burn for 4 to 7 minutes. Armored vehicles carried modified type 39 candles containing a mixture that burned more rapidly. Type 42 candle, produced late in the war, was a much larger munition, burning for 20 to 25 minutes.14
The Germans had a variety of launchers capable of ,tossing smoke pots 25 to 300 yards. These were first designed for armored vehicles. The original model was a bracket fastened to the side of the vehicle with 3 cups to hold candles. The device had to be loaded from the outside and was fired electrically, the candle being ignited and hurled about 25 yards by a charge of black powder. A later model resembled a miniature cannon. It was attached to a vehicle by a ring mount, and was loaded through the breech. Toward the end of the war, launchers for ground troops made their appearance. These were little more than crude mortars. The operator placed a powder charge in the bottom of the launcher barrel and then dropped an ignited smoke candle down the barrel, setting off a blast which threw the candle up to 300 yards.15
The German Army’s use of smoke pots was not unlike that of the American Army. Troops used smoke to cover withdrawals, as at Metz, to screen troops and supply movements against observation and air attack, to permit tanks to disengage from the enemy, and to divert the enemy’s attention and fire. As early as 1943 the production of smoke pots had
fallen behind the demand, and through the remainder of the war the German Army was unable to expend smoke with the same liberality as the American Army.
The Japanese Army had among its munitions grenades, candles, bombs, and shells filled with Berger-type or HC smoke mixtures. For producing screens it favored candles, of which there were 3 major types: the self-propelled candle, the rifle-launched candle, and the stationary candle. The self-propelled candle held 1½ pounds of smoke mix in one end and a propelling charge at the other capable of hurling the munition a distance of 130 to 300 yards, according to the angle at which it was fired. The rifle-launched candle was a cylinder 2 inches in diameter, 6 inches long, filled with smoke mix, and carrying from 45 to 200 yards, depending upon the adjustment of a heavy grenade launcher. Stationary candles came in 2 sizes, one holding 2 pounds of smoke agent, the other 7 times this quantity.16
While the Japanese gained considerable experience with smoke in their early campaigns against the Chinese, they made little use of it against American forces in the Pacific. Army and Navy raiding parties sometimes carried smoke grenades, ground troops on several occasions used smoke to confuse American air crews as to targets previously marked with smoke by American forces, and on Okinawa they screened local counterattacks and attempts at infiltration. The failure of the Japanese to make greater use of smoke screens in their tactics is surprising in view of the ample supplies of smoke munitions captured in Japanese ammunition dumps on Leyte, Luzon, and other islands.
The Army and Navy needed floating smoke pots to screen amphibious forces from enemy observation posts and artillery fire. Harbor defense units needed floating pots to assist in maintaining smoke rings against enemy planes. For these reasons the CWS undertook the development of this type of munition in 1942.
Engineers constructed the first experimental munitions from metal drums ballasted with concrete and loaded with HC. When tests proved these pots too heavy and difficult to handle, engineers simplified the design by discarding the concrete and only partially loading the drums so they were bottom-heavy and floated upright. The final model, M4, was a 5-gallon steel pail containing 26 pounds of smoke mix. To generate smoke the operator jerked a fuze wire extending through a hole in the lid and
Troops landing at Elba, June 1944. Note HC floating smoke pot at left of the LCIs.
tossed the can into the water. The pail bobbed to the surface and poured out white smoke through vents in the lid for ten to fifteen minutes.17
When floating pots came off the production line and entered supply channels, the Army and Navy found fault with the design. If the munition was handled roughly its HC filling crumbled, and the pot would not generate smoke. On several occasions firing mechanisms went off accidentally, igniting the pots and starting fires in warehouses, docks, and ships. To improve the munition, engineers placed a perforated, circular steel plate on top of the filling to hold it in place and devised a safer firing mechanism. The modified munition passed rough-handling tests satisfactorily and was standardized as the M4A1 in July 1943.18
The service found another source of trouble in the composition of the smoke mixture. Type B HC, the first filling used in floating pots, contained calcium silicide which could react with moisture in the atmosphere and generate hydrogen. Hydrogen and the air beneath the lid produced an explosive mixture. When the operator pulled the fuze wire the flame ignited the mixture, causing an explosion that sometimes blew the lid off the pot. As a precaution the CWS told operators to take off the lids and allow the hydrogen to escape before employing the smoke pots. This was inconvenient, particularly when a large number of pots had to be vented. The trouble was finally eliminated when chemists developed Type C HC to replace Type B.19
One other flaw in the floating pot was rather minor, yet it caused considerable annoyance to those who handled the munitions. The fuze stuck out from the center of the lid, preventing pots from being stacked in piles, and sometimes causing it to get knocked out of place. Engineers remedied this by lowering the fuze into a shallow well. This final model of the floating pot, designated as M4A2, was ready in March 1944.20
American forces used floating pots soon after they arrived in the Mediterranean area. After the invasion of Sicily naval patrol boats helped maintain smoke screens surrounding the harbors at Licata and Porto Empedocle by means of floating pots. At Salerno support boats dropped floating pots to form a screen that would protect landing craft from machine gun and artillery fire. The Third Army in its drive across France into Germany employed thousands of floating pots in assault river crossings, bridge construction, ferry operations, and other missions. The Ninth Army employed several thousand pots in crossing the Roer and Rhine rivers. Other armies set up floating screens whenever the occasion demanded. Since floating pots functioned on land as well as on water, troops often employed them in place of standard land pots when supplies of the latter ran low. While the M4 floating pot did not have the all-around usefulness of M1 and M5 land pots, it was a valuable munition in certain situations and it repaid the time and labor that went into its development and production.21
The German Army did not have floating munitions of the American
type which gave off smoke from a burning mixture, but they had a smoke float that generated white smoke by the action of water on fuming sulphuric acid or oleum. The float was a drum about 30 inches high, a foot in diameter, weighing 40 pounds empty and 80 pounds loaded. An inner container held the oleum which reacted with water, and emitted smoke for 8 to 9 minutes. The disadvantage of this type of munition lay in the corrosive action of the acid.22
Japanese troops were supplied both with floating pots that produced smoke from a burning mixture, and with floating generators that produced smoke by action of water. The Japanese floating pot, designed for use at sea or in rivers and harbors, was a long metal tube filled with eleven pounds of smoke mixture similar to the HC mixture used by the CWS. The novelty of the pot lay in the method of floatation. The pot fitted into a doughnut shaped, inflatable, rubber ring that held it upright and kept it from sinking to the bottom.23 The generator was a steel drum about a foot in height and in diameter, weighing ninety pounds when filled with fuming sulphuric acid. An inflated rubber ring could be attached to the float to increase its buoyancy. A small device inside the lid contained a material that burned slowly, giving off considerable gas. This gas built up pressure in the drum and forced the acid up a pipe that protruded above the float. Upon contact with air the acid formed a dense white cloud.24
Japanese and German forces did not employ floating smoke pots as extensively as American troops did. Early in the war enemy troops advanced and made amphibious landings without serious resistance, so that such aids as floating pots seemed unnecessary to them. Later as they retreated stubbornly and the American forces advanced, it was the Americans who used smoke pots to the best advantage.
Oil Smoke Generators
Smoke produced by the combustion of chemical mixtures was not the perfect answer to screening because mixtures were expensive, the smoke nauseated the troops, pots burned out in a short time, and many men were needed to maintain a large screen. On the other hand, it was easy and cheap to produce smoke by burning oil, and in 1941 the CWS
standardized an oil burner for this purpose. The Stationary Oil Smoke Generator, as the device was called, consisted of a sheet-iron pot about 2 feet in diameter and topped by a smokestack 3 feet high. The pot held about 15 gallons of crude oil. When the oil was ignited a mixture of black carbon smoke and oil droplets raced up the chimney and billowed out into the air. The volume of smoke was about equal to that given off by the M1 pot. The generator functioned like the smudge pots used in the South, to help protect citrus groves against frost. The British had produced a considerable number of similar smoke generators for defense of their island, and this was one of the factors that led the CWS to adopt this device.25
A few months after Pearl Harbor the CWS organized smoke generator companies, equipped each company with 3,600 oil smoke generators, and stationed them at the Panama Canal, the Sault Ste. Marie Canal, and around aircraft factories on the west coast. The generators did not go outside the continental United States or the Canal Zone. In maneuvers troops found that the large, heavy generators could not be moved quickly when the wind changed direction. Furthermore, the black smoke that they emitted did not have the obscuring power of white smoke. These disadvantages led the service to adopt a mechanical smoke generator in 1942 and abandon the stationary generator in 1944.26
Mechanical smoke generators came into existence through the cooperative efforts of industry, the National Defense Research Committee, and the CWS. The principle behind the device was simple. It vaporized a mixture of water and oil (the CWS used a special oil commonly referred to as fog oil), and then discharged the mixed vapors into the air. When the hot vapor hit the cool air it condensed back into tiny liquid droplets.
Mechanical generators had many advantages over oil burning generators. They produced smoke more rapidly and in larger quantity so that fewer men could screen a larger area. Their smoke was very persistent. By way of comparison, smoke from HC pots was seldom effective for more than 500 to 800 yards downwind, while smoke from mechanical generators extended for several miles.
Development of the first mechanical generators took more than a year. In 1941 the CWS received reports from the British of the Haslar
Mechanical smoke generator M1 (100-gallon) pouring out smoke screen to conceal Fifth Army operations from the Germans, Anzio area, Italy, March 1944.
generator, a 14-ton, cumbersome monster that produced dirty brown smoke from fuel oil and water. The CWS undertook the development of a generator based on the Haslar. In the meantime the NDRC, which had established a project on smokes and filters in 1940, was making progress on a different kind of generator. Associated with the NDRC were Irving Langmuir of General Electric Co. and Victor La Mer of Columbia University. These men and their associates studied the size and color of particles in artificial fogs to find the properties of droplets essential for maximum screening ability. Their final determinations ended the search for the ideal properties of particle size and color. They began their analysis with the knowledge that the effect of a smoke screen on the eye was partly physiological, partly optical, and partly psychological. Light from the sun struck the smoke, some of it passing through untouched, the remainder scattering in all directions. A person trying to concentrate on a target saw not only light reflected from the target but also the scattered light. The intensity of the scattered light determined the effectiveness of the screen in confusing and distorting the image. In their experiments, Langmuir and La Mer found that white particles .3 micron in radius produced the proper scattering effect.27
Langmuir and his co-worker Vincent J. Schaefer then devised a small generator capable of producing fog particles of the desired size. The model turned out a smoke screen much thicker and more permanent than the screen from the current oil burning generator. Upon request from NDRC the Standard Oil Development Co. rushed a full-size generator to completion in six weeks. In tests the generator performed so well that the CWS asked Esso to begin production at once. To obtain generators quickly, the CWS by-passed procedures generally followed in development, and engineers made last minute changes in design at the plant. In December 1942 the service standardized the apparatus for military use.28
Mechanical Smoke Generator M1 stood six feet high, weighing 3,000 pounds empty and 5,400 pounds filled. It had to be transported by a trailer, truck, or barge. At full capacity it consumed 100 gallons of fog oil, 7 gallons of fuel, and 150 gallons of water per hour. After starting, three to
six minutes elapsed before it warmed up and threw out an effective smoke screen.29
Generators first saw action in North Africa where CWS units used them in the smoke defense rings around Oran, Algiers, Bone, Bizerte, and other harbors. Later, the service used them for the invasion of Sicily. At Paestum in Salerno Bay, generator units operated for the first time under artillery fire, effectively concealing the anchorage and unloading areas from the Germans. The operation worked out so well that the Army decided to include a smoke unit in the forces assembled for the Anzio landing. In March 1944 mechanical generators threw up a protective haze between the town of Anzio and enemy lines. Thereafter the Army employed generators in front-area operations and to shield troop and convoy movments.30
The wide use of M1 generators in all kinds of weather and on all kinds of terrain in North Africa, Sicily, and Italy revealed shortcomings in the device. Mechanical flaws that normally would have shown up in development tests and have been corrected before the item was issued to troops now popped up in battle. More important, the heavy weight of the generators and the length of time they needed to warm up sometimes delayed the rapid deployment of troops, and on occasion prevented them from moving generators about on the battlefield. As a result the CWS and NDRC intensified their efforts to produce a lighter, compact generator that could be moved easily and make smoke quickly.31
In May 1943, the DeVilbiss and York-Hessian Companies built, under NDRC contract, small generators for trial. In September the Besler Corp. delivered to the CWS an experimental generator that the corporation had originally developed for the U.S. Navy. In comparative tests the Besler generator came out on top, and in January 1944 the CWS standardized it as model M2. The new generator was less than 3 feet long, 2 feet wide and 2 feet high. It consumed 50 gallons of fog oil, 5 gallons of gasoline, and 5 gallons of water per hour. Weighing only 180 pounds empty, 266 pounds full, it could be carried short distances by two men, whereas the M1 needed a vehicle. It could be employed in mountainous country or on soft ground, whereas the M1 could only be used on fairly flat, firm
Mechanical smoke generator M2 (50-gallon), one of many used to screen a heavy ponton bridge over the Rhine River, Germany.
ground. It produced smoke in less than 1 minute in contrast to the M1 which needed 3 to 6 minutes. On top of all these advantages it was simpler to operate and maintain in working order.32
The Fifth Army in Italy issued M2’s to smoke units in August 1944. The First Army received them in time for the landings in Normandy. As units received M2’s they gradually substituted them for M1’s. But all was not well. In action the new generators did not perform as efficiently as had been expected. They produced smoke for a few days, and then stopped. Frequently the coils in which the oil-water mixture was heated kept burning out. Poorly trained, careless operators caused some of the breakdowns while defects in the design of the generator caused others. As reports came in from the field, engineers at Edgewood corrected minor faults in the generator, though by the end of the war they were still not able to prevent coils from burning out.33
The Germans had large smoke generators for shielding oil refineries, blast furnaces, factories, canals, docks, and other important bomber targets. The principle behind their generators was entirely different from the one used by Americans. Instead of using oil they employed an acidic solution which fumed in moist air. The acid was stored in large barrels fitted with spray nozzles and connected to cylinders of compressed air which forced the acid out through the nozzles. Smoke from these sprayers has been described as resembling tobacco smoke. With a twenty-gallon drum of acid, a screen could be maintained for more than an hour. They did not generate smoke as rapidly as mechanical generators, the average length of time needed to set up an effective screen being fifteen minutes.34
German defenders ringed Berlin, Gdynia, Warnemunde, and other vital cities with acid spray generators generally spaced seventy-five to one hundred yards apart. At harbors such as Brest, sprayers on docks, breakwaters, and small fishing boats helped maintain the defensive circle. The smoke screens were not as thick as those thrown up by American mechanical generators, but the records show that they were helpful in cutting down the effectiveness of American bombing raids.35
The mechanical smoke generator was one of the innovations of World War II. It added a new dimension to smoke operations, making it possible for the Army to mass produce smoke for tactical and strategic operations. Judging from the increased use of generators as the war progressed, it seemed highly probable that mechanical smoke generators would be a standard piece of equipment in any future war.
Airplane Smoke Tanks
While smoke screens on land and sea were not new at the time of World War II, air screens were an innovation. Such screens, or curtains as they were frequently called, were set up by low-flying airplanes spraying liquid smoke-producing chemicals into the air. As the droplets floated to earth they reacted with moisture in the atmosphere and formed white smoke that hung suspended in the sky like a high, wide curtain.
The CWS began work on air smoke back in World War I when the Army considered smoke signals as a possible means of communication between planes or between planes and the ground. The service experimented with the idea, dropped it after the armistice, and then took it
up again in 1923 when the Navy asked for a smoke signaling device that could be mounted on a seaplane. During trial flights, engineers found that signal smoke formed so readily and had such good quality that it was worth investigating as screening smoke. The CWS continued to develop apparatus for airplane smoke screens long after the idea of smoke signals had been forgotten.36
Early devices injected liquid smoke agents into the exhaust of the plane. These soon gave way to simple spray tanks that emptied their contents directly into the air. The development of smoke tanks then received impetus from the fact that they could also be used to spray liquid toxic agents, such as mustard, on enemy troops. In other words, the Army could employ them on defensive missions to drop air curtains, or on offensive missions to drop toxic chemicals. In World War II the Army and Navy employed tanks only for the former purpose, but they were on hand in case gas warfare broke out.
The CWS had two smoke agents for spraying. Titanium tetrachloride (symbol FM) had been known to chemists for almost a century before European armies placed it in World War I artillery shells to throw up a white smoke and thus assist observers in directing fire. It reacts immediately with water vapor, forming several white compounds that remain suspended in air as a dense white cloud. The service employed FM as its first agent in the 1920s, but the disadvantages—excessive cost and the tendency of solid reaction products to clog spraying apparatus—sent chemists in search of a replacement. In 1930 the service decided on FS, a solution of sulphur trioxide in chlorosulfonic acid. When atomized in moist air the ingredients reacted with water vapor forming minute droplets of sulphuric acid that, like FM, also appeared as a dense white cloud. During World War II the CWS procured supplies of both agents, two thousand tons of FM, and twenty-four thousand of FS (some of which went into smoke bombs and grenades).37
The standard airplane spray tank was, at the time of Pearl Harbor, model M10, holding about thirty gallons of liquid and streamlined in accordance with formulas recommended by the National Advisory Committee on Aeronautics. The CWS had begun development of this tank in 1937 at the request of the Air Corps and later, lacking time and
Lockheed A-29 spraying smoke from M33 smoke tanks visible under wings of craft. Smoke tank protruding from bomb bay is the M33 A-1.
personnel, had contracted with the Douglas Aircraft Co. to complete it. The A-20 Douglas Havoc or any other plane equipped with suitable carrying racks and controls could take the spray tank aloft. An inlet in the front admitted air, and an outlet in the tail pipe released the spray. Glass disks blocked both holes until the pilot pressed an electrical switch, sending a current through detonators attached to the glass. Air rushed through the inlet into the tank forcing the filling out through the tail pipe. The rate of discharge varied with the velocity of the plane, dropping from 5½ seconds at 175 miles per hour to 4 seconds at 325 miles per hour. With FS smoke agent, the maximum height at which the plane could fly to produce an effective curtain was about 300 feet. Some of the smoke billowed upward so that the completed screen towered about 400 feet in the air and stretched about 2,000 feet along the ground. Model Mb was the most popular of the CWS’s smoke tanks, more than 90,000 coming from plants during the war.38
While the CWS was readying a smoke tank for the Army, the Navy,
which had never lost its early interest in air curtains, designed two tanks somewhat larger and based on a different principle than the CWS’s M10. One of these held fifty gallons, the other thirty gallons. The plane carried a cylinder of compressed carbon dioxide gas, the pressure of which ejected the smoke agent. With this system the pilot could turn the spray tank on or off at will, releasing the agents in puffs or in one long burst.
The CWS adopted the Navy tanks for the Army, modifying them for bomb bay installation (the Navy used belly mounting) and designating them as models M20 and M21. In 1942-43 the service procured more than six thousand of each model. Experience showed that the tanks were cumbersome, the cylinders of carbon dioxide were an annoyance in supply channels, and the smoke screens were not sufficiently thick. The CWS stopped production of the tanks and declared them obsolete in 1944.39
The tanks that have been mentioned were designed originally for external mounting on planes. Some years before the war the CWS had considered mounting tanks in bomb bays for smoke spraying or toxic spraying, but it discarded the idea because of the danger to crew and plane in case the tank was pierced by enemy fire. In 1939 a conference of Air Corps and CWS officers decided to go ahead with the idea. The work proceeded slowly owing to a combination of circumstances: the runway at Edgewood Arsenal had to be enlarged to accommodate multi-engine planes, the CWS had to obtain an isolated proving ground for high altitude spray tests, and the Army needed bombers abroad so badly that it would not assign one for the test project. Not until 1942 was the experimental model ready, and not until 1944 did production begin. This new tank held seventy gallons of agent, and could set up a smoke screen 400 feet high and 4,000 feet long in one minute. The bombardier could drop the tank if necessary before or after the mission. Later the CWS modified the tank so that it could be suspended from wings of aircraft, and thus decrease contamination of the plane from spattering and lessen the danger to aircrews. Industry produced more than ten thousand of the bomb bay type (M33) and wing type (M33A1).40
The M10, M20, M21, and M33 smoke tanks gave the Army a range of from thirty to seventy gallons, but wartime bombers were capable of carrying tanks of considerably greater size. Accordingly the CWS designed and tested, but did not produce in quantity, a tank (M40) holding more than 200 gallons (4,000 pounds) of FS for B-17 and B-24 airplanes. With its large capacity, this tank could set up a screen much longer and thicker than could smaller tanks.41
The armed forces used aerial smoke curtains on many operations in Europe and in the Pacific. In the Marshalls carrier planes laid screens to shield landings at Roi-Namur. As a prelude to amphibious landings on Guam, Okinawa, and Borneo, planes laid down smoke to conceal underwater demolition teams. In Italy the Air Forces placed a screen behind Cisterna to shield the 7th and 15th Infantry. At Nadzab, near Lae, New Guinea, at Kamiri airstrip, Noemfoor, and at the Camalaniugan airfield near Aparri, Luzon, aircraft sprayed smoke to protect paratroop landings.42
American forces far outdid German and Japanese armies in the use of aerial smoke screens in World War II, although the enemy was also equipped for such operations. The Germans had several spray tanks of different sizes which, like American tanks, could have been used for toxic agents or smoke agents. Their liquid agent was a solution of sulphur trioxide in acid, similar to the CWS’s FS smoke agent. The Japanese had at least one aircraft spray device, as well as agents like FS and FM. The reason the Germans did not use aerial smoke seems to have been the fact that their armies had been successful in invasions and paratroop drops, as at Crete, without smoke curtains, and by the time they had learned the value of such curtains from American successes, they were on the defensive. The Japanese could have employed aerial smoke on many of their island invasions, but again their success in invasion by conventional means may have made them oblivious of the potential value of air curtains.43
Airplane spray tanks were not as widely or as frequently employed as smoke pots, grenades, mechanical generators, and other ground smoke munitions. In amphibious landings, paratroop drops, and situations where a wall of protective smoke had to be erected quickly between American and enemy forces, smoke tanks nonetheless proved to be valuable, efficient devices.
Colored Smoke Munitions
The Chemical Warfare Service’s experience with colored smokes began in 1917 when it developed red, yellow, blue, green, and black smoke signals for the AEF.44 In carrying out this work the CWS stepped into a field of munition research already occupied by the Ordnance Department. Therefore in 1920, when Congress made the CWS a permanent branch of the Army, the War Department found it necessary to set up a boundary between the two organizations. The Secretary of War assigned to the Ordnance Department all smoke devices used in signaling and spotting, to the CWS all smoke devices used in screening.45 As a result of this ruling and of a lack of interest on the part of the using arms the CWS did little with colored smokes during the 1920s and 1930s. But shortly before World War II the service received requests from the Army Air Forces and from the Armored Force for colored smoke munitions. With the cooperation of Ordnance, CWS again undertook work on colored smokes.46
During World War II, colored smoke grenades were the signal munitions most commonly used by American troops. The CWS began development in September 1942 when the Army Ground Forces requested smoke grenades that could be used to show troop positions, to identify American tanks, or to signal the location of forced-down planes. The major problem facing the service was to find a mixture of chemicals that would produce smoke of the desired color, volume, visibility, and duration. This necessitated a search for heat-stable, commercially available, inexpensive dyes, and for a fuel which would burn with sufficient intensity to volatilize but
not to decompose the dye. Dyes were not synthesized in the Edgewood laboratories, but were obtained from industry. Industrial cooperation was extremely important since the CWS needed a large quantity of dye. For example, since each colored smoke grenade required seven-tenths of a pound of dye the CWS had to purchase approximately three and one-half million pounds of dye to fill the five million grenades produced during the war. Other signal muntions greatly increased the total poundage of dyestuffs so that industry had a problem in producing all the special dyes that the CWS needed.47
Engineers fashioned the first smoke grenades from the standard chemical warfare M7 grenade. This was a steel cylindrical can 45/8 inches high and 2 Ys inches in diameter. They punched a number of holes in the sides to give the volatilized dye a short path through the hot ash, and thus keep the dye from burning. The fuel consisted of sulphur and potassium chlorate, with sodium bicarbonate to absorb some of the heat and keep the temperature down. The ignited grenade emitted a cloud of smoke for approximately 2 minutes. The CWS standardized the munition as the M16 in April 1943, and produced it in 6 colors, red, orange, yellow, green, violet, and black.48
After the production of the M16 grenade had gotten underway, the Army Ground Forces studied the performance of the munition in service tests and decided that it would be more useful if the rate of smoke production was increased. It was impossible to raise the volume of smoke by speeding the combustion because a higher temperature would have caused excessive decomposition of the dye. However, the rate of smoke production could be increased by changing the design of the grenade body, the proportion of the ingredients in the mixture, and the pressure under which the mixture was compressed. In the new design, engineers eliminated the side holes and cut one large hole, one-half inch in diameter, down through the middle of the filling. The finished grenade, designated as Model M18, gave off a dense volume of smoke for approximately one minute. The CWS planned to produce eight colors, but later at a conference of Air Forces, Navy, British, and CWS representatives it was
decided to reduce the number to four contrasting colors, red, yellow, green, and violet.49
Colored smoke grenades were employed in every kind of signaling by troops in the field, but the most common use lay in communicating with planes that provided close air support. Planes had to recognize American front lines, artillery positions, and tanks or else they might bomb them accidentally. American forces generally showed yellow smoke to protect themselves from their own planes. Troops found other uses for smoke in marking targets for artillery fire, in communicating with tanks, and in signaling other troops. An indication of the value of colored smoke grenades is the large number, more than five million, produced by the CWS from 1942 to 1945.50
Infantrymen found it difficult to throw colored smoke grenades very far. In 1943 upon request of the Army Ground Forces the CWS undertook the development of rifle grenades that could carry several hundred yards. Model M22, the first produced in quantity, was similar in appearance to the M9A1 antitank rifle grenade. It could be sent off by means of the M7 or M8 grenade launcher, from either the M1 rifle or M1 carbine, and upon impact let off colored smoke—red, orange, yellow, green, or violet—for more than one minute. A later model, M23, intended for use in jungle or thick forest where high trees and thick underbrush would hide smoke from hand grenades, released a stream of colored smoke as it arched across the sky. It remained in flight about eleven seconds, reaching an altitude of five hundred feet. Four colors were produced: red, yellow, green, and violet. Filling plants loaded more than one-half million of the impact and the streamer grenades in 1944 and 1945.51
The difficulties the CWS faced in finding suitable smoke mixtures for grenades were duplicated in the work on colored artillery shells, mortar shells, rockets, and bombs. Chemists had to formulate mixtures that would release smoke of the desired density for the required time, and engineers had to cope with mechanical obstacles that appeared in casings. Artillery shells posed no unusual problem. Technicians took a base-ejection shell
developed years before and substituted colored smoke canisters (steel tubes filled with smoke mixture) for white smoke canisters. The shell, in flight, ejected and ignited the canisters which then gave off colored smoke. The shell released its canisters several hundred yards from the target, but the canisters continued to fly through the air and fell close to the point where the projectile landed. The service developed several experimental and standard canisters for base-ejection shells of different calibers, but actually produced only those for 105-mm. and 155-mm. shells. These came in red, yellow, green, and violet. More than two million 105-mm. canisters and almost seven hundred thousand 155-mm. canisters passed along the filling lines. Artillery employed these shells widely in Europe and in the Pacific for indicating targets within enemy territory where black or white bursts could have been confused with the usual smoke of battle.52
Artillery shells were only one type of marking and signaling ammunition developed by the CWS. For units in the Pacific, engineers devised 2.36-inch colored smoke rockets to mark positions of units or locations of front lines in dense jungle where smoke from hand grenades could be seen not at all or with great difficulty. Rockets of one type smoked upon impact, those of the other type left a trail of smoke as they flew through the air. For the Army Ground Forces the CWS designed colored smoke shells to fit 60-mm. and 81-mm. infantry mortars, and 4.2-inch chemical mortars. The demand for rockets and shells did not materialize, and the CWS closed the projects without getting into production.53
Although infantry and artillery made most use of colored smokes, aviators saw the possibility of using signals for communicating with the ground or with other planes. The Navy asked for a 100-pound colored smoke bomb that could be dropped on beaches to identify areas where troops could be landed quickly. The CWS produced experimental models, but then dropped the project when the Navy changed its mind about the need for such bombs. The Army Air Forces requested a smoke missile that could be used in pattern bombing over Europe. In this method of
bombing, all planes in the formation released their bombs simultaneously upon signal from the lead plane. A colored smoke bomb dropped by the leader appeared to be a feasible means of giving the signal. In 1944 the CWS started work on this bomb. Engineers took the Ordnance M38A2 100-pound practice bomb, and replaced the sand ballast with pellets of colored smoke mixture. When dropped, the bomb left a trail of colored smoke. Since smoke from this first model was too tenuous to be seen clearly by all planes in a flight, engineers placed a tube in the long axis of the bomb and filled the tube with a string of red and yellow smoke grenades. The first grenade ignited when the bomb left the bay, and the other grenades ignited in succession, leaving an easily visible trail in the sky. Before the war was over the CWS produced fillings for several thousand M87 colored smoke streamer bombs.54
The German Army, as the American, had a variety of air and ground colored smoke signals. The most common munitions were small candles about two inches in diameter and holding a few ounces of smoke mixture. The candles, for the colors red, green, blue, and violet, produced smoke for about twenty seconds. German forces employed single colors or combinations to send a variety of signals. An orange smoke candle, issued in three sizes, was used only to send distress signals. For artillery signaling, marking, and ranging, the Germans had 7.5-cm. and 10.5-cm. shells with red and blue smoke fillings, fused for either air burst or impact. In the fighting in Europe, German artillery attempted to cross up signals between American planes and troops and cause planes to bomb American-held territory by firing colored smoke shells into the American lines. All in all, the Germans found colored smoke quite as useful as did the Americans.55
The Japanese seemed to have favored colored flares fired from grenade dischargers in their signaling; consequently they did not have as large a variety of colored smoke munitions as the Americans or the Germans. The standard candle was a cylindrical can six inches high, two inches in diameter, and containing a few ounces of red, blue, or yellow smoke mixture. Smoke from these candles was not as thick or persistent as American smoke. The Japanese made up for the lack of variety in their signal
grenades, shells, and bombs by the large variety, at least fifteen, of 50-mm. signal flares that could be seen for several miles, day or night.56
Colored smoke munitions were of small importance when compared to the CWS’s 4.2-inch chemical mortars, mechanical smoke generators, incendiary bombs, toxic agents, gas masks, and other items, but they proved their usefulness in special situations and contributed to the success of American troops throughout the war.
The armed forces made significant advances in the evolution of smoke tactics during the war. Progress resulted largely from the introduction of two new smoke producing devices, the mechanical smoke generator and the airplane spray tank, and the improvement of conventional smoke munitions and agents. The old and new devices gave the army munitions for almost every conceivable type of operation so that smoke as a military tactic became far more valuable than at the start of the conflict.
The subjects of the previous chapters—chemical agents, incendiaries, smokes, chemical mortars, flame throwers, biological agents—were the chief concern of the CWS during the war. They do not, however, represent the entire scientific program. At times the service carried out other investigations. One of these was begun in December 1944 when the Air Forces asked the CWS to develop propellants for the JB-2 flying bomb, the American counterpart of the German “buzz bomb.” A group of scientists, headed by Maj. Frederick Bellinger, investigated three systems of liquid propellants: hydrogen peroxide-permanganate, fuming nitric acid-aniline, and mononitromethane-catalyst. The FRED project (after Frederick Bellinger) ended with the successful launching of the JB-2 bomb at Eglin Field.57 Another unusual project had to do with the production of iron carbonyl, needed by the Signal Corps. The only commercial source then available was the General Aniline and Film Co. plant at Linden, N.J., managed and operated by German aliens. To assure a steady supply of the compound the Defense Plant Corporation tried to develop the process, but proceeded so slowly that Secretary of War Patterson transferred the project to the CWS. The service cooperated with a chemical engineering
firm in producing the product.58 Another group of projects had to do with researches on insecticides, miticides, and rodenticides. The CWS was represented on the Army Committee on Insect and Rodent Control, established in November 1944, and also cooperated with the OSRD’s Committee on Insect and Rodent Control.59
In the approximately four years of World War II the CWS carried on far more technical work than during the previous twenty years of peace. But it could have accomplished even more had there been a larger research and development organization at the start of the war. The service tried to overcome its early handicap by spending large amounts of money, but funds could not buy time.
The Chemical Warfare Service came out of the war with the largest technical organization it had ever had. Its leaders, many of whom had grown up with the service, were impressed with the need for maintaining such an organization lest the mistakes of the past be repeated. They did not want to suffer a repetition of the post World War I experience.