Chapter 22: The Reduction of the Shimbu Group; Phase II: The Seizure of Wawa and Ipo Dams
Having turned the Shimbu Group’s left and having virtually destroyed the Noguchi Force, XI Corps reoriented its attack. General Hall now planned to strike generally north toward Wawa Dam, destroying the Kobayashi Force on the way and simultaneously clearing sufficient terrain to assure the security of the area west of the Bosoboso River. Hall designated an objective line stretching from Mt. Oro, three and a half miles north of Wawa Dam, south-southeast for fifteen miles along the first dominating high ground east of the Bosoboso. About 90 percent of the terrain to this new line lay within the 6th Division’s zone. That division would have to drive north from Mt. Baytangan to Mt. Oro; advance across the Bosoboso River to clear Mt. Purro, lying just southeast of and controlling the confluence of the Bosoboso, Marikina, and Montalban Rivers; reduce known Kobayashi Force strongpoints at Mts. Mataba and Pacawagan; and, last but not least, seize Wawa Dam. The 43rd Division, for the time being, would do little more than mop up on the Shimbu Group’s left in order to protect the 6th Division’s right rear.1
Protecting the Right Rear
During the period from 24 through 31 March the 103rd Infantry, 43rd Division, provided considerable protection to the 6th Division’s right rear with the seizure of Hill 1200, on the east bank of the Bosoboso River a little over a mile east of barrio New Bosoboso.2 The regiment set up a combined roadblock and patrol base just north of Hill 1200 on a road that Shimbu Group forces employed as their main route of withdrawal into the Sierra Madre. An improved horse trail, this road ended at
Santa Iñez, on the Lenatin River eight rough, mountainous miles northeast of New Bosoboso. The road marked the boundary between the 6th and 43rd Divisions in the region east of the Bosoboso River. Elements of the 43rd Division continued patrolling in the area south of the Santa Iñez road until 2 May, when the entire division redeployed to the Ipo Dam front. Its operations from 27 March through 2 May cost the 43rd Division about 30 men killed and 120 wounded; the division killed approximately 830 Japanese during the same period.
Ultimately, the 112th Cavalry RCT took over in the region south of Hill 1200, while elements of the 38th Infantry Division moved into the area between Hill 1200 and the Santa Iñez road. Continuing to patrol eastward, the 112th Cavalry found no traces of organized Japanese resistance. By the end of May the regiment had killed about 170 Japanese stragglers in the area it covered, itself losing 2 men killed and 12 wounded.
The operations in the region south of the Santa Iñez road were not spectacular, but they served the purpose for which they were designed. Without the security the patrolling actions on the right rear provided, the 6th Division and other XI Corps units would have been unable to bring to bear their full strength against the Kobayashi Force and the Wawa Dam defenses.
Breakthrough in the Center
The 6th Division Strikes North
The 6th Division’s first plans for the capture of Wawa Dam called for the 1st and 20th Infantry Regiments to drive northward abreast, the 1st Infantry on the east.3 With its right on the Bosoboso River, the 1st Infantry was to strike north across a front a mile and a half wide. (Map 16) The terrain in the regiment’s zone was dominated by a partially wooded, steep-sided ridge line running north-northwest from Mt. Baytangan, the regiment’s line of departure. The first section of the ridge north of Mt. Baytangan the 1st Infantry soon dubbed Woodpecker Ridge after the large number and constant chatter of Japanese machine guns that characterized the defenses. The regiment hoped it could quickly clear Woodpecker Ridge as far as dominating ground just southwest of the Bosoboso-Marikina confluence, ground that also controlled the upper reaches of the Mango River in the 20th Infantry’s zone.
The 20th Infantry’s first major objective was Mt. Mataba. Part of the regiment was to strike toward this objective along a 1,000-foot-high bare ridge leading west-northwest from Mt. Baytangan. The ridge gave way to an open-sloped north-south ridge line, the northern end of which lay a mile east of Mt. Mataba’s crest and joined that crest across a saddle over 750 feet high. As of 28 March, when the 6th Division’s new attack was to start, the 20th Infantry already had one infantry company on the north-south ridge at a knob a mile and a half southeast of Mataba’s peak.
The 63rd Infantry would support the 20th Infantry by executing diversionary attacks along the western slopes of Mt. Mataba. General Hurdis, the 6th Division
Map 16: The Seizure of Wawa Dam, 27 March28 May 1945
commander, hoped that the attacks would force the Kobayashi Force to disclose the location of machine gun, mortar, and artillery emplacements, thereby permitting the division’s supporting aircraft and artillery to deliver timely and accurate fire for the 20th Infantry. The 6th Reconnaissance Troop, for similar purposes, would probe east across the Bosoboso River toward Mt. Purro, which overlooked all the 1st Infantry’s zone.
Intense small arms, machine gun, and mortar fire, occasionally augmented by accurate harassing artillery bombardments, characterized the resistance the 1st and 20th Infantry Regiments encountered during the week beginning 28 March.4 Operations seesawed back and forth as the American units gave ground that proved untenable, but then attacked to regain the same ground. At the end of the week Japanese resistance seemed stronger than when the attack began. The 20th Infantry had moved less than half a mile toward Mt. Mataba, and the 1st Infantry had secured hardly 250 yards of ground in a northerly direction. Both regiments were becoming bogged down.
General Hurdis had hoped his attack, directed against the Kobayashi Force southern flank, would be far more successful, but the Kobayashi Force, rapidly and efficiently, had reoriented its defenses, which it had laid out primarily to face an attack from the west.5 The force’s two remaining provisional infantry regiments, the Central and Right Sector Units, were still relatively intact, and the Central Sector Unit, bearing the brunt of the 6th Division’s offensive, had recently been reinforced by remnants of the Left Sector Unit and elements of the Shimbu Group Reserve.
Other factors bearing on the 6th Division’s slow progress were the declining strength and deteriorating combat efficiency of its infantry regiments. The 20th Infantry could muster only 2,085 effectives on 3 April; some of its rifle companies were reduced to the combat strength of platoons. The situation within the 1st Infantry, with an effective strength of 2,150, was little better. As of 3 April the commanders of both regiments rated their units’ combat efficiency only as “fair,” the lowest ranking of three terms each had employed since the Lingayen Gulf assault.6
The XI Corps and the 6th Division would have to make some changes if the division were to continue the offensive, and during the period 3-5 April, Generals Hall and Hurdis effected some of the most necessary ones. First, General Hall reduced the 6th Division’s front, organizing a provisional brigade composed of the 112th Cavalry RCT and the 169th RCT, 43rd Division, to take over the area north of an east-west line across Mt. Oro, a line that corresponded closely to the boundary between the
Terrain Defended by Kobayashi Force
Kobayashi and Kawashima Forces. Hall placed the brigade under the command of Brig. Gen. Julian W. Cunningham and designated the provisional unit Baldy Force.7 Cunningham’s commands were almost always “cursed” with this name, for the general, like Friar Tuck, had just a fringe of hair around his pate.
The change of boundaries on the north released the bulk of the 63rd Infantry for General Hurdis’ use in a new attack against the Kobayashi Force. The 63rd Infantry had about 2,425 relatively fresh combat effectives as of 3 April and was ready for a good scrap. Hurdis directed the unit to relieve the 20th Infantry and continue the attack north toward Mt. Mataba. For the time being the 1st Infantry would hold the little ground it had gained along Woodpecker Ridge and confine its activities to patrolling.8
From 6 through 9 April the 63rd Infantry made only limited advances and on the 10th switched the emphasis of its attack to a drive up the western slopes of Mt. Mataba. Over a month earlier the 1st Infantry had failed in an attempt to take Mt. Mataba from the west, but now the 63rd Infantry, moving forward behind a heavy artillery preparation, found the mountain’s bare western slopes weakly defended. On 10 April the regiment secured the southwestern quarter of the mountain, but then discovered that the Kobayashi Force still retained a remarkable degree of maneuverability. Having pulled many troops out of its western defenses to meet the attack from the south, the Kobayashi Force quickly transferred strength back to Mt. Mataba from the north-south ridge. The Japanese did not have sufficient strength to hold both terrain features for long, but they were able to keep the 63rd Infantry off Mt. Mataba’s crest until 17 April.
The 63rd Infantry’s success at Mt. Mataba on the 17th was accompanied by a renewed 1st Infantry effort to drive north along Woodpecker Ridge. The effort failed, and by the end of the day it became evident that until supporting artillery and aircraft could reduce many more defenses in the 1st Infantry’s zone the regiment could gain ground along Woodpecker Ridge only at the risk of prohibitive casualties. For the second time in two weeks General Hurdis ordered the 1st Infantry to halt.
Hurdis hoped to move immediately against Mt. Pacawagan and Wawa Dam, but he again faced personnel problems. As of 17 April the 1st Infantry’s effective strength was 2,190; the 63rd Infantry had less than 2,335 effectives; and the 20th Infantry, built back up to a strength of 2,485 effectives, still needed rest. The rifle companies of the 1st Infantry averaged only 105 effectives apiece, the 20th Infantry’s were at 125, and the 63d’s companies could muster less than 120 effectives each.9
The problem was solved in somewhat the same fashion that it had been on 3 April. The 145th Infantry of the 37th Division came out of Manila, and the 20th Infantry of the 6th Division went into the city to take up garrison duties. Out of combat for over a month, the
145th Infantry had an effective strength of 3,000 troops and, rested, was ready to strike into the mountains against the Shimbu Group. General Hurdis directed the regiment to move on Mt. Pacawagan from the west; he ordered the 63rd Infantry to provide the new arrivals with fire support from Mt. Mataba; and he instructed the 1st Infantry to hold and patrol pending the outcome of the 145th Infantry’s attack. The latter was to have the following support:–10
Division and Corps Artillery
3 105-mm. howitzer battalions
2 155-mm. howitzer battalions
1 155-mm. gun battery
1 240-mm. howitzer battery
1 8-inch howitzer battery
2 90-mm. AAA gun batteries
From the 63rd RCT on Mt. Mataba
5 M7 105-mm. SPM howitzers of Cannon Company
8 81-mm. mortars
8 4.2-inch mortars
2 57-mm. AT guns
11 .50-caliber machine guns
12 .30-caliber heavy machine guns
The support fires almost pulverized Japanese defenses on the western and southern slopes of Mt. Pacawagan, yet the 145th Infantry, starting its attack on 21 April, could not secure a hold on much of the mountain until the 30th. Even then, the Kobayashi Force maintained positions on the extreme northeastern peak and on a spur hill about three-quarters of a mile south-southeast of the northeastern crest. The gains through 30 April had cost the 145th Infantry 55 men killed and 220 wounded – in nine days the regiment had incurred more casualties than had any regiment of the 6th Division for the entire month of April.
During the 145th Infantry’s attack the 1st and 63rd Infantry Regiments had continued to hold the ground they already occupied until relieved late in the month by the 151st and 152nd Infantry Regiments of the 38th Division. On 30 April responsibility for further offensives against the Kobayashi Force and toward Wawa Dam passed from the 6th to the 38th Division.11
Having virtually destroyed the Kobayashi Force’s Left Sector Unit by the end of March, the 6th Division and its attachments had made significant strides during April toward the elimination of the Central and Right Sector Units. In fact, the Japanese unit designations had apparently lost meaning by the end of April and Headquarters, Kobayashi Force, had taken over direct control of defensive operations in front of Wawa Dam. That Japanese force had lost about 3,000 men killed from 28 March through 30 April, and had given up important defensive terrain. The casualties of American units engaged against the Kobayashi Force from 28 March through 30 April were:–12
| Unit | Killed | Wounded | Total |
| 1st Infantry | 40 | 115 | 155 |
| 20th Infantry | 40 | 130 | 170 |
| 63rd Infantry | 35 | 140 | 175 |
| 145th Infantry | 55 | 220 | 275 |
| 151st Infantry | ... | ... | ... |
| 152nd Infantry | 5 | 10 | 15 |
| Total | 175 | 615 | 790 |
When relieved by the 38th Division, the 6th Division was in poor shape. Morale was down, men and officers alike were tired and worn, and all units were sadly understrength, especially in combat effectives. Since 22 February the 6th Division had suffered approximately 1,335 combat casualties – 335 killed and 1,000 wounded – and over three times that number of men had been evacuated from the front lines either permanently or temporarily for noncombat injuries, sickness, and psychoneurotic causes. The Sixth Army’s twin millstones of the Luzon Campaign – lack of combat replacements and lack of strength to effect timely rotation of units in contact – had weighed heavily upon the division.
The 38th Division Attacks, 1-18 May
During the period 1-3 May the 38th Division executed probing attacks in preparation for a concerted drive toward Wawa Dam beginning on the 4th.13 XI Corps, anticipating quick success in this new attack, estimated that the bulk of the Kobayashi Force had either already withdrawn or was in the process of retreating east across the Bosoboso River. The corps also estimated that the Japanese unit maintained only small delaying attachments west and south of Wawa Dam.
The XI Corps’ estimates were quite inaccurate. Far from abandoning the ground in front of Wawa Dam, General Yokoyama was preparing a limited counteroffensive in the form of a series of harassing, delaying actions. Yokoyama felt that the Kobayashi Force was strong enough for at least one more good fight. Since 20 February the force, together with its attachments from the Noguchi Force and the Shimbu Group Reserve, had lost over 7,000 men killed but, having been reinforced from time to time, still had a strength of at least 6,500 men as of 3 May. These troops formed a cohesive unit, not, as XI Corps had estimated, a group of isolated delaying detachments. Finally, the remaining elements of the Shimbu Group Reserve, some 3,000 men located at or near Mt. Purro, backed up the Kobayashi Force,
One of the reasons that prompted General Yokoyama to undertake another counteroffensive despite the miserable failure of his previous two attempts would undoubtedly have embarrassed XI Corps had that corps learned of it. Yokoyama had not been impressed by the corps’ progress during April. On the contrary, he had become perturbed at what he termed a lull in operations on his western front. So marked had this lull seemed to Yokoyama that by the end
of April he had decided that XI Corps must be moving the bulk of its troops to northern Luzon, if not off Luzon altogether. If so, Yokoyama had failed to execute his primary mission – to pin down a sizable number of U.S. forces for a protracted period. The only way Yokoyama could find to avert this failure was to stage limited counterattacks to forestall further XI Corps redeployment and to force the return to the Shimbu area of American units that might already have moved north.
The Shimbu Group commander planned no attempt to retake and hold lost ground. Rather, he hoped that with a series of strong infiltration attacks he could create so much chaos and confusion within the XI Corps area that his ends would be realized. He directed his troops to execute their operations during the hours of darkness and to hide out during the day. The infiltration attacks were to begin on 10 May, and all participating units were to be reassembled in their original positions by the 25th.
On 10 May two battalions of Kawashima Force were to begin harassing the 38th Division’s left rear north of Montalban to cover preparations for the Shimbu Group’s main effort, which was to start on the 12th. The principal striking force of the main body would be the understrength 31st Infantry of the Shimbu Group Reserve and three or four battalions – averaging less than 300 men apiece – of Kobayashi Force. These units were apparently to converge upon the town of Marikina. What was left of the Noguchi Force would provide additional support for the main effort by launching raids along XI Corps’ southern flank.
As had been the case with Yokoyama’s mid-March counterattack,14 everything went wrong with his early May effort. Again, he did not have the slightest inkling of XI Corps intentions. He did not know, for example, that the corps was redeploying the 43rd Division to the Ipo Dam front to begin an offensive there before the end of the first week of May; he had no idea that the 38th Division was to start an all-out drive toward Wawa Dam on 4 May; he had wrongly guessed that XI Corps was transferring troops away from the Wawa Dam front. Indeed, the whole course of Yokoyama’s planning at this juncture seems to indicate that the Shimbu Group was no longer capable of acquiring even the most rudimentary elements of tactical intelligence.
During the XI Corps’ probing attacks of 1-3 May the 145th Infantry, 37th Division, secured all those portions of Mt. Pacawagan having the greatest military value to both the Kobayashi Force and the 38th Division, to which the 145th was now attached. At the same time the 152nd Infantry, 38th Division, had made gains of half a mile on Woodpecker Ridge.15 The 145th Infantry was now to strike directly east to seize Wawa Dam, and the 152nd Infantry was to continue north along Woodpecker Ridge in a supporting attack. Two battalions of the 151st Infantry guarded the flanks of the 38th Division; the third held at Mt. Mataba.
On 4 May the 145th Infantry gained up to 1,000 yards along the northern and
northeastern slopes of Mt. Pacawagan, but could secure little new ground in an easterly direction.16 The 152nd Infantry advanced about 500 yards northward along Woodpecker Ridge. These gains, unspectacular as they were, had a profound effect upon the Shimbu Group’s plans. Suddenly, Yokoyama realized that XI Corps had mounted a serious, immediate threat to his center. Since the threat had been developing for over a month, it is difficult to ascertain just what caused Yokoyama to change his mind about XI Corps dispositions and intentions. Probable contributing factors were the intensity of the artillery preparations for the 38th Division’s attack of 4 May, the scale of the artillery and mortar support provided the 145th and 152nd Infantry Regiments throughout the 4th, and the gains made by the 38th Division after 1 May. Whatever the reasons, Yokoyama on 4 May directed his forces to initiate their infiltration attacks immediately instead of waiting until 10 May.
While the Japanese were hurriedly trying to move into position for their attacks, the 145th Infantry struck eastward to seize the rocky pinnacle of Mt. Binicayan, rising sharply to a height of 1,250 feet on the south bank of the Marikina River at Wawa Dam. With its equally rocky twin, Mt. Pamitinan north of the Marikina, Mt. Binicayan dominated the Marikina Valley from the northeastern slopes of Mt. Pacawagan to the Marikina-Bosoboso junction. Accordingly, the 145th Infantry’s seizure of Binicayan’s crest on 9 May was a substantial achievement, and the loss was one the Kobayashi Force could ill afford. Indeed, that Japanese unit had expended most of its efforts during the period 5-9 May in a vain and costly attempt – 400 men killed – to keep the 145th Infantry off Mt. Binicayan. The fact that the Kobayashi Force had failed to defend Binicayan in greater strength was a tactical mistake of considerable magnitude. Rising sheer from the gorge of the Marikina at Wawa Dam, the cave-pocked, rocky peak, adequately defended, would have proved virtually impregnable. Moreover, adequate defenses on Mt. Pamitinan, across the river, could have rendered much of Mt. Binicayan untenable for the 145th Infantry.
Probably one reason the Kobayashi Force had not been able to hold Mt. Binicayan was that much of its strength had been redeploying to take part in Yokoyama’s scheduled counterattack. But the Kobayashi Force’s share in the counterattack effort never got off the ground. That unit shot its bolt defending Mt. Binicayan and Woodpecker Ridge, and the 145th Infantry never knew it was being counterattacked. In the 152nd Infantry’s sector action followed different lines. Operating against Japanese defenses on the ridge – and now undertaking wide envelopments instead of costly frontal assaults – the 152nd ran headlong into troops of the Shimbu Group Reserve who were moving west across the Bosoboso River to take part in the counterattack. The new arrivals
6th division approach to Wawa Dam
slowed the 152nd Infantry, while at the same time the Japanese found it necessary to fight hard even to hold the ground from which their infiltration attacks were to be launched. In the end, counterattack action in the 152nd Infantry’s sector was limited to a series of dawn and dusk raids beginning on 14 May and lasting about a week.
Elsewhere across the XI Corps front, the Shimbu Group’s effort had no effect. By the time the Kawashima Force’s two battalions were ready to move south, the 43rd Division had struck toward Ipo Dam, pinning the Japanese units to that front. On the far south, the Noguchi Force remnants were unable to make any significant contributions. Recognizing that the whole affair had proved futile, Yokoyama on 15 May ordered all units involved to withdraw immediately, orders that apparently did not reach the Shimbu Group Reserve units operating in the Woodpecker Ridge area for almost a week. Nevertheless, Yokoyama had achieved some degree of success. By delaying the progress of the 152nd Infantry along Woodpecker Ridge, the Japanese had also delayed the capture of Wawa Dam, for Maj. Gen. William C. Chase, commanding the 38th Division, believed it too risky to push the 145th Infantry to the dam until the 152nd had cleared Woodpecker Ridge. The period of the counterattack – roughly 4 through 18 May – cost the 145th, 151st, and 152nd Infantry Regiments approximately 85 men killed and 305 wounded; the Kobayashi
Force lost almost 1,300 men killed during the same period.
Wawa Dam and Beyond, 19-31 May
The 38th Division faced some perplexing tactical problems at evening on 18 May. The 145th Infantry held a dangerously exposed salient at Mt. Binicayan, and almost a mile of rough terrain separated the regiment from the 152nd’s forward elements on Woodpecker Ridge.17 The Japanese could still move forces in between the 145th and 152nd from the east side of the Bosoboso River. At the same time, General Chase felt it necessary to either overrun or neutralize Japanese positions on the high ground north of Wawa Dam before launching a final attack toward the dam. The only good supply route over which he could support the final attack to seize the dam was a narrow gravel road running along the south bank of the Marikina from Montalban to the dam. The Japanese controlled the road by artillery, mortar, and machine gun fire from the heights north of the dam.
So far, General Chase had been unable to stage any offensive north of the Marikina. The lay of the ground there, together with the location of Japanese defenses in the area, required that any advance be made across a front extending north from Mt. Pamitinan four miles to Mt. Oro. To 18 May, the 38th Division had been unable to place more than one battalion of the 151st Infantry in the region, a force patently too small to attack across so broad a front.
Shortages of artillery and 81-mm. mortar ammunition had also played a major part in General Chase’s decision not to launch an offensive north of the Marikina. He had had trouble providing adequate ammunition to support the operations of the 145th and 152nd Infantry Regiments during the period 4-18 May, and the shortages had helped prompt him to keep his 149th Infantry in reserve during that period. The shortages were, perhaps, not as critical as the 38th Division commander believed. One of the reasons the Japanese gave for the failure of their May counterattack was that American artillery had broken up the effort before it was well under way.
General Chase finally decided that once the 152nd Infantry’s attack to clear Woodpecker Ridge had gained momentum, the 151st Infantry, less one battalion, would launch a drive in the area north of the Marikina to clear Mt. Pamitinan and Mt. Hapanong–Banoy, three quarters of a mile to the north. The 149th Infantry would relieve the 145th in place and, after the attacks of the 151st and 152nd showed promise of certain success, the 149th would descend on Wawa Dam, its flanks secured and its supply route safe.
On 19 and 20 May the 152nd Infantry continued enveloping maneuvers at Woodpecker Ridge while 38th Division engineers bulldozed roads to the front lines to permit medium tanks, flame thrower tanks, and half-tracks mounting multiple .50-caliber machine guns to make their way forward. With this close fire support (the flame thrower tanks
proved especially effective), the 152nd Infantry resumed frontal attacks along the ridge on 21 May. Japanese resistance began to collapse. The next day the collapse turned into rout, and by 25 May the regiment controlled the junction of the Marikina and Bosoboso Rivers. From the 25th until the end of the month the regiment outposted the west bank of the Bosoboso from this confluence south to Mt. Baytangan and sent patrols across the Bosoboso to feel out Japanese strength at Mt. Purro.
The 151st Infantry had initiated its drive north of the Marikina on 21 May. By the 26th its troops were on the western slopes of Mts. Pamitinan and Hapanong–Banoy, and Japanese resistance began to melt away. The 149th Infantry struck toward Wawa Dam on the 27th and, encountering no opposition, secured it intact at midmorning on the 28th. The last remnants of the Kobayashi Force had withdrawn.
General Yokoyama had had little choice but to order a retreat after the failure of the Kobayashi Force to achieve lasting results with the mid-May counterattack. The force’s front had, indeed, virtually collapsed by 22 May. At the same time the Kawashima Force, on the Ipo Dam front, was proving incapable of holding back the 43rd Division. With his right and center breaking apart just as his left had folded at the end of March, General Yokoyama, on 27 May, ordered a general withdrawal. Organized remnants of the Kobayashi Force in the Wawa Dam area acted on these orders during the following night, pursued on subsequent days by patrols of the 38th Division. By 31 May General Chase had ample evidence to conclude that the Kobayashi Force had withdrawn. Wawa Dam, he knew, was secure beyond the shadow of a doubt; in the future the 38th Division would mop up and pursue rather than make concerted attacks against organized Japanese lines.
The May operations to secure Wawa Dam had cost the 38th Division, including the attached 145th Infantry of the 37th Division, some 750 combat casualties – 160 killed and 590 wounded. During the month the Kobayashi Force had lost another 3,000 men killed in ground action alone, while countless others had died of starvation, disease, or as the result of American air and artillery bombardment. At the end of May the Kobayashi Force had followed the Noguchi Force into oblivion as an effective combat unit; as of 31 May Headquarters, Kobayashi Force, had under its control an organized group of less than 3,000 troops. The Shimbu Group Reserve had also suffered heavily during the month and probably could not muster over 1,500 effectives. Meanwhile, the Kawashima Force had suffered heavily at the hands of the 43rd Division.
The Seizure of Ipo Dam
The 43rd Division’s redeployment to the Ipo Dam front in early May had been a departure from General Hall’s plan for the destruction of the Shimbu Group and from General Krueger’s schedule of operations for the seizure of the components of the Manila water supply system. Both plans had called for the seriatim destruction of the Shimbu Group’s three western front forces by steady attack from south to north. Thus, from XI Corps’ point of view, the 43rd Division’s displacement had been premature, and the decision to move the division
northward had been forced upon General Hall by higher headquarters.
Offensive and Defensive Plans
The necessity for initiating a drive on Ipo Dam before completing operations to seize Wawa Dam stemmed from Manila’s water supply problems. By mid-April an acute water shortage had developed within the city. Informing General Krueger of this problem, General MacArthur told the Sixth Army commander that south of the Pasig Manila was without water except that supplied by Army tank trucks and shallow, usually contaminated wells. Sewage disposal throughout the city was becoming increasingly difficult because water pressure from the overtaxed Novaliches Reservoir – the only dependable source – was insufficient to carry off refuse. Flush toilets were clogged; many citizens had to employ gutters and esteros for defecation. Restaurants and night clubs, happily and heavily patronized by off-duty American troops, were finding it impossible to maintain minimum sanitary standards. The problems increased with a steady, continued influx of military units and civilians to the metropolitan area. There was very real danger that severe epidemics might break out within the city at any moment.18
On 19 April General MacArthur suggested to Krueger that the Sixth Army could solve Manila’s water supply problems by seizing “the reservoir in the Montalban area,” and went on to ask Krueger how soon that installation would be captured.19 The query puzzled Krueger, who now knew that the only true reservoirs tied into the Manila water system lay west of the Marikina River and had been in American hands since February. Krueger had also learned that the water supply installation nearest Montalban – Wawa Dam – was no longer connected to the metropolitan system. He therefore asked General MacArthur if by the phrase “reservoir in the Montalban area” the theater commander meant Ipo Dam, the only major water installation still in Japanese hands.20 Krueger’s question apparently prompted further study of Manila’s water system at GHQ SWPA, and on 22 April MacArthur radioed Krueger that Ipo Dam was the preferred objective. The capture of the Ipo installation, MacArthur went on, would solve Manila’s water supply problems.21
Upon receiving MacArthur’s message, Krueger directed XI Corps to launch a drive on Ipo Dam as soon as possible.22 General Hall, in turn, ordered the 43rd Division (less the 169th RCT, already on the Ipo front) to redeploy northward from the corps’ right flank. He simultaneously disbanded the provisional Baldy Force and instructed General Cunningham’s 112th Cavalry RCT to take over the positions on the south vacated by the 43rd Division.
Another factor urged an early attack toward Ipo Dam – the rainy season would be under way by the end of May. The generally open terrain in the Ipo Dam area, full of rocky outcroppings and cut by the gullies of innumerable, intermittent, wet-weather streams, was every bit as rough as that on the approaches to Wawa Dam and, although not as high, gave promise of being even more difficult in bad weather. The 43rd Division knew of the need for speed, but the time the division required for its preparations made it impossible for General Hall to schedule the beginning of the attack any earlier than 7 May.
The most logical avenue of approach to Ipo Dam was Route 52, a two-lane graveled road running generally northeast from Manila through Novaliches and on to the dam. About six miles northwest of Montalban, Route 64, coming in from the west, joined Route 52 at a junction long known as Hot Corner because Kawashima Force artillery had had the junction zeroed in even when the 1st Cavalry Division had passed by on its way to Manila in the early days of February. Route 52 ran north from Hot Corner about five miles to Bigti, whence it swung northeast and east to the dam, four and a half miles distant. Route 65-B led northwest four miles from Bigti to Norzagaray on the Angat River, the waters of which Ipo Dam diverted into an aqueduct about seven miles east of Norzagaray.
Before the 43rd Division moved north, Baldy Force had held outposts along the line Norzagaray–Bigti–Hot Corner, and during the period 7-12 April had undertaken a reconnaissance-in-force from this line toward Ipo Dam. Then Baldy Force had discovered that the Kawashima Force had thoroughly fortified the Route 52 approach to the dam and obviously expected an attack astride that road.23
The 43rd Division’s subsequent search for another route of advance was a discouraging task. The vegetation throughout the area was tropically lush, although spotty. Even on the brightest days the entire region, sparsely inhabited and unsuited to agriculture, bore an oppressive, weird aspect. Wildly tossed rock outcroppings were the pervading feature. Some stretching horizontally across the land, some pyramiding dizzily to sudden, jumbled heights, these dark grayish outcroppings and sharp pinnacles looked like the product of a fantastic nightmare induced by studying a Dali portraiture of the moon’s surface. Formed of both sharp-edged rock slabs and rounded boulders of all imaginable sizes and shapes, and sometimes so brokenly piled as to provide much of their own bulk with shadow, the outcroppings often supported a sufficient verdure of brush and trees to give Japanese defenders concealment from the prying eyes of American ground and air observers. By the very nature of their structure the formations, even the most bare, also supplied the Japanese with many a cave hideaway. Depressing – although not without a touch of wild, desolate beauty – the terrain looked downright unhealthy. To realize that a strong, well-armed Japanese force defended the region only lent an additional foreboding tone to the whole.
The generally rising ground and a high range of partially wooded hills that ringed Ipo Dam on the north, east, and south controlled all the approaches to
Approaches to Ipo Dam
the dam from Norzagaray south to Hot Corner. From this ground the Kawashima Force’s artillery, mortars, and machine guns could deliver devastating, observed fire against the 43rd Division. An attack between the Bigti-Ipo Dam stretch of Route 52 and the Angat River, to the north, would have to be channeled through a two-mile-wide corridor in rocky, partly open ground dropping off to the steep-sided, boulder-strewn gorge of the Angat. North of the stream the terrain, more wooded, was so rough and broken that it seemed to preclude the employment of large units. South of the Bigti-Ipo Dam stretch of Route 52 the ground was quite open, trackless, and rough. Here, engineers would have to bulldoze supply roads over and around rocky outcroppings, working up rising terrain where Japanese could observe every movement.
Nevertheless, General Wing, the 43rd Division’s commander, decided to make his main effort south of Route 52. He reached his decision primarily because the April reconnaissance-in-force had disclosed that Kawashima Force defenses south of the road were considerably weaker than those in the vicinity of the highway. Furthermore, he hoped that a drive from the south might achieve tactical surprise, for the Japanese might not expect attack through the inhospitable, forbidding ground south of Route 52.
The 103rd Infantry, on the division’s right, would make the main effort. Striking from a line of departure about two miles east of Hot Corner, the 103rd would drive east four miles to Mt. Katitinga, at the southern end of a broken, rocky ridge line stretching four miles northward to the Angat Gorge at Ipo Dam. Once at Mt. Katitinga, the regiment would use the ridge line as its principal route of attack toward the dam. The 172nd Infantry, in support, was to strike toward the dam across a two-mile-wide front on the 103rd Infantry’s left, advancing first east-northeast and then swinging north to cut Route 52 about midway between Bigti and the dam in order to isolate strong Japanese defenses in the vicinity of Bigti. The 169th Infantry, on the 172nd’s left, would demonstrate along Route 52 to help pin down the Japanese in the Bigti region.
General Wing had another force at his disposal, a guerrilla regiment that had been active with the 43rd Division on XI Corps’ southern flank. Aided by the 43rd Division in the matters of arms and training, the regiment, commanded by Col. Marcus V. Augustin, was known as Marking’s Fil-American Yay Regiment – short title Marking Regiment.24 Wing planned to employ the regiment in an operation that he originally intended as a feint. Crossing the Angat River near Norzagaray, the Marking Regiment would drive eastward north of the river toward Mt. Kabuyao, three and a half miles north of Ipo Dam, and would be prepared to exploit whatever success it might achieve. Elements of the Marking Regiment would also probe eastward along the south bank of the Angat. The guerrillas’ operations would be conducted under the direction of Brig. Gen. Alexander N. Stark, the assistant commander of the 43rd Division.
To enhance the chances for tactical surprise, the 43rd Division, less the 169th RCT, moved northward in small increments between 2 and 5 May, assembling behind a line of outposts the 169th Infantry maintained. The division kept reconnaissance to a bare minimum, and units deployed along their lines of departure under cover of darkness in preparation for jumping off during the night of 6-7 May. A night attack in terrain not thoroughly reconnoitered was known to be risky, but the desire to achieve surprise overrode other considerations. Artillery would mark initial objectives of the night attack with white phosphorus and thus offset the lack of reconnaissance to some extent. In the actual event, this worked better than the 43rd Division had hoped, but the artillery’s markings were admittedly no substitute for complete reconnaissance.
Speed was as important as surprise to General Wing, for he did not want to give the Japanese time to redeploy defensive forces. Finally, Wing was willing to employ mass against the Kawashima Force’s prepared defenses. He realized he might be inviting heavy casualties, but he had to accept the risk in the light of the urgent need for the early capture of Ipo Dam.
Before 6 May the Kawashima Force had no idea that a full American division
was assembling on the Ipo Dam front.25 On that day, the Japanese unit had some 7,000 effectives left – the 43rd Division estimated 5,250 maximum – of the 9,000 troops assigned to it on 20 February, and most of the 7,000 were south of the Angat River. The northern anchor of the defenses was a group of small hills on the Angat’s south bank three miles north of Bigti. Elements of the Kasama Battalion (the reinforced 358th Independent Infantry Battalion, 105th Division), which contained the Kawashima Force’s only “regular” infantry, held this anchor. South of the hills the Hanabusa Detachment, one of the Kawashima Force’s two provisional infantry regiments, maintained defenses across Route 52. The other provisional regiment, the Tomono Detachment, extended the defenses for about two miles south and southeast of the Bigti area. The main strength of the Kasama Battalion held the ground southeast of the Tomono Detachment to the ridge along which the 103rd Infantry was to advance. The southern end of this ridge – the Mt. Katitinga area – was defended at first by the Narukami Battalion of the Hanabusa Detachment. The region north of the Angat was the responsibility of the Muroya Battalion, which operated under the direct control of Kawashima Force headquarters. The bulk of the Muroya Battalion was stationed on high ground on the north bank of the Angat to close the open, northern end of a horseshoe-shaped bend around which the river flowed on its way across Ipo Dam.
In accordance with General Yokoyama’s counterattack plan of 4 May, the Kawashima Force had ordered the Narukami Battalion south toward Montalban. The three days of heavy air attack that preceded the 43rd Division’s assault made it impossible for the Japanese unit to assemble for its move south, and on the evening of 6 May the battalion’s march was barely under way. Guessing then that a major attack was about to hit him, Maj. Gen. Osamu Kawashima, the Kawashima Force commander, called off further attempts to send troops southward to participate in the Kobayashi Force’s efforts to delay the progress of the 38th Division toward Wawa Dam.26 It was on this note that the Kawashima Force belatedly began to prepare to meet the 43rd Division’s attack, which began at 2200, 6 May.
The First Phase, 6-14 May
Exploiting the element of surprise the night attack achieved, the 103rd and 172nd Infantry Regiments made excellent progress during the first day of the offensive.27 (Map 17) The 103rd Infantry encountered only scattered opposition,
Map 17: The Seizure of Ipo Dam, 6-17 May 1945
gained the western slopes of Mt. Katitinga and, bypassing the rest of that mountain, sped up the ridge line to rocky, wooded Hill 1000, less than three miles south of Ipo Dam. The 172nd Infantry at dusk on 7 May was nearing the foot of a rocky ridge two miles southeast of Bigti. North of the Angat, the Marking Regiment met no resistance as it marched over seven miles eastward, halting for the night only a mile and a half northwest of Mt. Kabuyao, its initial objective. The only significant resistance the 43rd Division’s units had encountered during the day had been at Hill 535 where, on the south bank of the Angat three miles north of Bigti, part of the Kasama Battalion had repulsed a company of the Marking Regiment.
Japanese opposition had proved so unexpectedly weak that the 43rd Division pressed its attack through the night of 7-8 May, and continued its advance without letup through the 11th. Then rough terrain, unseasonably early and heavy rains, and increasingly stubborn resistance combined to slow the 103rd Infantry. By evening on the 11th the regiment’s left was up the north-south ridge line to Hill 805, two miles south of Ipo Dam; the right had moved east across the tiny Ipo River and had reached Hill 810, two miles south-southeast of the dam. Meanwhile, right flank elements of the 172nd Infantry had advanced to the southwestern slopes of rocky Hill 815, half a mile north of Hill 805. Left flank units had begun probing into Japanese defenses on Fork Ridge, two miles east of Bigti and falling away on the north to a boulder-strewn stream bed. North across this stream lay Osboy Ridge, overlooking Route 52 from the south. Patrols of the 169th Infantry had already discovered that the Kawashima Force’s principal defenses ran across the western slopes of Osboy Ridge – the ridge would have to be cleared before the 172nd Infantry could safely push its left any further northward.
The Marking Regiment, north of the Angat, had met with unexpected success. Overrunning a Japanese outpost on Mt. Kabuyao, the guerrilla unit on 11 May reached the Muroya Battalion’s main defenses at Four-Corner Hill, less than two miles north of Ipo Dam. During the day the guerrillas mounted three assaults at Four-Corner Hill, but at dusk, having lost 25 men killed and 55 wounded, they withdrew.
By evening on the 11th General Wing knew that all elements of the 43rd Division were in firm contact with the Kawashima Force’s main line of resistance. The thrust from the south had gone well so far, but opposition there was stiffening – the Kawashima Force, at first caught off balance, had begun to transfer troops eastward from the Bigti-Osboy Ridge area to meet the threat posed by the 103rd Infantry. Hoping to halt these Japanese movements, Wing directed the 169th Infantry to increase the strength of its demonstrations and to mount a limited attack at Osboy Ridge. At the same time he took another look at the role of the Marking Regiment. What had started out as a feint from which no significant results were necessarily expected, now bid fair to become as much a part of the main effort as the 103rd Infantry’s drive north. The attack toward Ipo Dam, originally conceived as one depending for success upon the 103rd Infantry’s progress, had developed into a full-fledged double envelopment.
Indeed, a race for the dam was on between the Marking Regiment and the 103rd Infantry.
On 12 May the guerrilla unit, for the first time amply supported by 43rd Division artillery, broke through the Four-Corner Hill defenses, losing another 15 men killed and 75 wounded and killing about 80 Japanese. The remnants of the Muroya Battalion – probably not 400 strong to start with and now reduced to about 100 effectives – fled southward to Hill 803, half a mile north of Ipo Dam. Elsewhere on the 43rd Division front, gains on 12 May were relatively unimportant.
For the Kawashima Force, all was not necessarily lost when the Marking Regiment had seized Four-Corner Hill. General Kawashima probably had sufficient strength to hold the guerrillas at Hill 803 for some time; he could have begun sending reinforcements to that hill on the 12th. But from the content of orders he received from Shimbu Group headquarters, the 12th of May must have seemed ruinous to Kawashima.
Because of communications or intelligence failures, General Yokoyama had not yet learned that a reinforced U.S. division was attacking the Kawashima Force. Furthermore, the Shimbu Group commander still felt that the Kobayashi Force front was of more vital importance than that of the Kawashima Force. Since the situation in the Kobayashi Force zone was critical, and since his scheduled counterattack against the 38th Division had virtually collapsed by 12 May, General Yokoyama directed the Kawashima Force to launch a new counterattack against the left and left rear of the 38th Division on 14 May. With his own defenses crumbling, General Kawashima unsuccessfully tried to argue Yokoyama into canceling the order. Upon the failure of his pleadings, Kawashima reluctantly directed the Kasama Battalion to undertake the attack against the 38th Division.
The main body of the Kasama Battalion moved out of its lines west of the Ipo River during the night of 12-13 May, forded the Ipo near the dam, and assembled on high ground behind the Narukami Battalion. The move was covered by night attacks against the 103rd and 172nd Infantry Regiments; elements of the Hanabusa Detachment spread thinly eastward in an attempt to take over the Kasama Battalion’s positions.
The effect of the redeployment was about what General Kawashima had expected. On 13 May the 103rd Infantry swept across Hill 805 to Hill 860, digging in for the night hardly three-quarters of a mile south of Ipo Dam. Simultaneously, the 172nd Infantry’s right flank cleared most of Hill 815. Elsewhere south of the Angat American troops made only minor gains, but north of the stream the Marking Regiment captured the crest of Hill 803.
General Kawashima had seen enough and, without asking Yokoyama’s permission, directed the Kasama Battalion to return to the lines southwest of Ipo Dam. Maj. Tetsuyuki Kasama, a commander of some initiative, had anticipated these orders by ten or twelve hours. From a vantage point southeast of the dam he had been watching the American attack develop on the morning of the 13th when he learned that the last Narukami Battalion positions on Mt. Katitinga, controlling his route of march southward, had fallen. Kasama
Ipo Dam
had therefore halted his battalion and at dusk on the 13th started back west across the Ipo River.
The Kasama Battalion was dismayed to find many of its old defenses in the Hills 815-860 area occupied by 43rd Division troops, but attacked in a futile effort to regain the lost ground. When dawn broke on the 14th the Kasama Battalion, having lost over 100 men during the night, could muster no more than 250 effectives. These survivors dug in along the slopes of Hill 860 and, fighting fanatically, held the 103rd and 172nd Infantry Regiments to minor gains on 14 May.
Meanwhile the Marking Regiment, on a technicality, had already won the race to Ipo Dam. Taking advantage of Japanese preoccupation south of the dam during the night of 13-14 May, a guerrilla patrol crept down the southern slope of Hill 803 and made its way across the Angat via the dam. The patrol found the dam intact and the powerhouse on the south bank largely undamaged. Too weak to hold the installations, the patrol returned before dawn to the crest of Hill 803, where the rest of the regiment had its hands full mopping up.28
Securing Ipo Dam, 14-31 May
Late on 14 May the 43rd Division paused to make new attack plans.29 So far the division had made little progress toward Route 52, and it now seemed necessary and timely to commit the 169th Infantry to an attack to clear the road to the dam. First, the division urgently needed the road as a route of supply and evacuation. Ever since its attack had begun, rains had intermittently halted ground and aerial supply, evacuation, and air support operations. Hampered by the weather and the rough terrain, division engineers had been unable to construct and maintain supply roads at a pace commensurate with the infantry’s advances. Airdrops and hand-carry had kept the combat units’ supplies at the minimum required level, but evacuation of sick and wounded remained a major problem. Finally, on 14 May, the entire division area was weathered in, and for the first time since 6 May the Fifth Air Force was unable to fly a single air support or air supply mission.
Second, the 43rd Division knew that sizable groups of the Tomono and Hanabusa Detachments had shifted from their Route 52 defenses to meet the 103rd and 172nd Infantry Regiments’ attacks from the south. General Wing therefore felt that the 169th Infantry, striking directly along Route 52, would have a far easier and less costly task than it would have faced a week earlier. In addition, an attack by the 169th could forestall further Japanese redeployments eastward, speed the capture of Ipo Dam, and draw off Japanese troops from Fork Ridge, where the 172nd Infantry’s left was bogged down.
General Wing directed the 103rd Infantry to secure the Route 52 terminus at Ipo Dam, take the dam, and then clear the high ground north of the road and west of the dam. He ordered the 172nd Infantry to seize Hill 804, whose northern slopes Route 52 crossed at a point two miles west of the dam. The 169th Infantry was to clear the last Japanese defenders out of the Bigti area and then drive eastward along Route 52 to gain contact with the 172nd. Wing evidently expected that the 103rd Infantry could accomplish its missions on 15 May; the attacks of the 169th and 172nd Infantry Regiments were to start on the 16th, but poor weather conditions, which forced cancellation of air strikes on the 15th, prompted Wing to postpone those two regiments’ jump-off until the 17th. Lack of air support, together with supply problems, also made it impossible for the 103rd Infantry to get under way before the 17th.
More concentrated air support than previously provided during any attack against Shimbu Group positions preceded the 43rd Division’s offensive of 17 May.30 On the 16th, for example, about 185 fighter-bombers of the Fifth Air Force dropped some 50,000 gallons of napalm on Japanese defenses in the Bigti-Osboy Ridge area. Later the same day other planes bombed and strafed Japanese artillery emplacements in the vicinity of Hill 804, employing three tons of fragmentation bombs. Starting at 1030 on the 17th about 240 fighter-bombers dropped over 62,500 gallons of napalm along and near Route 52 in the Hill 804 area and on Japanese positions northwest of Hill 804. During the afternoon ten light bombers hit Japanese defenses a mile north of Bigti and then returned to strafe. Although sodden ground and vegetation in the target areas somewhat inhibited the spread and fury of napalm fires, the 43rd Division thought the napalm strikes to be remarkably effective.
Meanwhile, XI Corps and 43rd Division Artillery had stepped up the pace of their support fires, and during the period 15 through 17 May expended ammunition about as follows:–31
| Weapon | Rounds |
| 90-mm. antiaircraft guns | 740 |
| 105-mm. howitzers | 5,865 |
| 155-mm. howitzers | 2,000 |
| 155-mm. guns | 955 |
| 155-mm. GPF gun | 15 |
| 8-inch howitzers | 145 |
On 17 May the principal success of the 43rd Division’s attack came at Ipo Dam, a success that created a minor controversy between the 103rd Infantry and the Marking Regiment. At midmorning on the 17th the 103rd, having cleared the last Japanese from Hill 860, sent a small patrol down the hill’s steep, grassy northern slopes to the south end of the dam. Out of contact with the rest of the regiment and unable to find any signs of friendly forces in the dam area, the patrol returned to the top of Hill 860 almost immediately. Then, shortly after noon, a second patrol of the Marking Regiment came down the slopes of Hill 803 on the opposite side of the Angat, waded across the river at the dam and, about 1330, raised the American flag over the powerhouse on the south bank. The 103rd Infantry noted this activity and sent a large combat patrol back down Hill 860 to establish contact with the guerrillas. When this patrol reached the powerhouse at 1530, nearly 250 men of the Marking Regiment were on the ground at both sides of Ipo Dam.32
Out of loyalty to his troops Col. Joseph P. Cleland, the 103rd Infantry’s commander, sought a major share of the credit for the capture of Ipo Dam, radioing to General Wing:
We’re not conceding anything to guerrillas. We had patrols at [the] dam this morning and saw no guerrillas. When we returned this evening they were there.33
Whatever Cleland’s opinion, the Marking Regiment has to be given the lion’s share of the credit for the capture of Ipo Dam. The regiment was the first to have troops at the dam – the night patrol of 13-14 May – and was the first to permanently occupy the ground at the dam. On the other hand, it is certain that the Japanese would still have been holding the dam at dark on 17 May had not the Marking Regiment and the 103rd Infantry attacked in concert toward that objective.
With the capture of Ipo Dam intact, the 43rd Division had accomplished its major mission. The Japanese had prepared demolitions at both the dam and powerhouse but had failed to set them off. The 43rd Division had taken an important step toward solving Manila’s water supply problems, but before the division could assure the security of the dam and the aqueduct to Novaliches Reservoir, it would have to clear Kawashima Force remnants from the region west of the dam. Moreover, the 43rd Division had not yet secured Route 52, and supply and evacuation problems were becoming daily more vexing.
The task facing the 43rd Division proved easier than anticipated. The Kawashima Force was split by the line of the ridge running south from Ipo Dam to Mt. Katitinga; its units west of the line had been disorganized and demoralized by the air and artillery bombardments, especially the napalm strikes, of 16-17 May. Finally, General Kawashima had decided that further efforts to hold Ipo Dam would be futile. Either late on the 16th or early on the 17th he had ordered what was left of his command to withdraw to an assembly point on the western slopes of Mt. Maranat, three miles east of the dam.34
Events moved rapidly during the next four days as isolated elements of the Kawashima Force began infiltrating eastward through the 43rd Division lines while the division set about the messy job of mopping up. The division opened Route 52 from Bigti to Ipo Dam on the 19th and by the 21st had cleared the last organized resistance from the area west of the dam and south of the Angat. North of the river the Marking Regiment had little trouble mopping up. Many Japanese ostensibly trapped as of 17 May certainly escaped eastward, but the 43rd Division killed or found dead 850 Kawashima Force troops in the area west of Ipo Dam from 18 through 21 May. Since 6 May, when the 43rd Division had begun its attack, the Kawashima Force had lost over 2,000 men killed and approximately 40 captured. The 43rd Division’s casualties for the period from 6 through 21 May were:
| Regiment | Killed | Wounded | Total |
| 103rd Infantry | 25 | 105 | 130 |
| 169th Infantry | 15 | 80 | 95 |
| 172nd Infantry | 30 | 150 | 180 |
| Marking | 40 | 145 | 175 |
| Total | 110 | 480 | 590 |
The 43rd Division continued its mopping-up operations through 31 May, patrolling eastward across the Ipo River, northeast up the Angat from the dam, and throughout the area over which the worst fighting had taken place. The Kawashima Force, having no offensive intent, confined its activities to reassembling east of Ipo Dam in preparation for further retreat deep into the Sierra Madre. During the last ten days of May the 43rd Division killed or found dead approximately 725 Japanese and captured 75 others; the division’s own losses were roughly 10 killed and 35 wounded.35
The Destruction of the Kogure Detachment
By the end of May XI Corps had destroyed as effective combat organizations the Shimbu Group’s four strongest subdivisions – the Kawashima, Kobayashi, and Noguchi Forces and the Shimbu Group Reserve. While XI Corps had been devoting its main energies to the defeat of these western front Shimbu forces, part of the corps, and later elements of XIV Corps, had undertaken to destroy the Shimbu Group’s fifth major component, the Kogure Detachment. Originally deployed to protect Shimbu Group’s left rear against attack from the Bicol Peninsula, the east coast of Luzon, and the eastern shore of Laguna de Bay, the Kogure Detachment, in late March, had lost half its best troops by transfer to the Noguchi Force, then in desperate need of reinforcement.36 Filipino guerrillas, 43rd Division patrols, Allied aircraft, and an increasingly high rate of sickness had further depleted the Kogure Detachment until, by 1 April, the unit had scarcely 800 effectives left of its original strength of 2,250.
Operations against the Kogure Detachment entered into the campaign against the Shimbu Group in a rather
indirect fashion. About 10 March elements of XIV Corps had initiated an offensive against Shimbu Group’s semi-detached Fuji Force in southern Luzon.37 By the end of the month the XIV Corps units had driven well east across Luzon in the region south of Laguna de Bay. Retreating before XIV Corps’ pressure, some 2,000 men of the Fuji Force had employed Route 21, running north along the eastern side of Laguna de Bay, and the Santa Maria Valley, centering on the northeastern shore of Laguna de Bay, as avenues of escape from southern Luzon.
General Krueger believed that these Fuji Force troops had joined the main body of the Shimbu Group in the mountains east of Manila, that more men of the Fuji Force would try to join the group, and that Japanese forces on the Bicol Peninsula might also make their way northwestward to the Shimbu Group’s lines. Krueger’s G-2 Section estimated that as many as 10,000 Japanese could reach the Shimbu Group western front from southern and southeastern Luzon. Even if poorly armed and equipped, these Japanese could hardly provide XI Corps with any aid and comfort as that unit continued its offensive against the Shimbu Group’s main body. Accordingly, Krueger laid plans to stop the possible flow of Japanese reinforcements around the eastern and northern shores of Laguna de Bay. He directed XI Corps to clear the northern shore of the lake, block the Santa Maria Valley, and close Route 21 by making firm contact with XIV Corps along the lake’s eastern shore. General Hall, commanding XI Corps, assigned the tasks to the 43rd Division, which in turn made the 103rd RCT responsible for the execution of the missions.38
Having completed its share in the operations to destroy the Noguchi Force, the 103rd Infantry turned to its new job on 30 March.39 Taking elaborate precautions to avoid alerting the Kogure Detachment, the regiment displaced eastward along the northern shore of Laguna de Bay in small increments. At 0400 on 4 April the regiment began moving into the Santa Maria Valley, catching the Japanese there completely by surprise. (Map 18) By midmorning the 103rd was in Siniloan, at the northeast corner of Laguna de Bay. Two days later, after two or three sharp skirmishes with Fuji Force troops coming north from southern Luzon, the 103rd made contact with XIV Corps units near Pagsanjan, at Laguna de Bay’s southeastern corner. From 6 through 21 April, when elements of XIV Corps relieved it, the 103rd Infantry patrolled throughout the Santa Maria Valley and probed northeastward from Siniloan along Route 455, leading to the east coast of Luzon at Lamon Bay. Its share in the operations to block Japanese movements around Laguna de Bay cost the 103rd Infantry about 10 men killed and 20 wounded; the regiment killed some 240 Japanese in scattered contacts.
Map 18: To Infanta and Santa Iñez, 31 March-18 June 1945
The most surprising development during the 103rd Infantry’s operations was the discovery that the Kogure Detachment would make no real effort to defend the Santa Maria Valley and environs, an area from which the Shimbu Group had hoped to replenish its rapidly dwindling food stocks. Instead, the detachment had withdrawn to good defensive positions at Kapatalin Sawmill, four miles up Route 455 from Siniloan, to block that road to Lamon Bay. In the light of the effective strength left to it, the detachment’s decision to evacuate the open Santa Maria Valley region seems quite sound.
XIV Corps, as it moved troops to the Santa Maria Valley on 21 April, hoped to mount an immediate drive toward Lamon Bay, but until 6 May could spare only the 7th Cavalry Regiment, less one squadron, from its commitments in southern Luzon. On the 6th the 8th Cavalry took over in the valley, and the
entire 7th Cavalry began the postponed drive along Route 455.40
Japanese defenses at Kapatalin Sawmill were located in hilly, densely jungled terrain at a horseshoe-shaped bend of Route 455. The ground and defenses bore striking resemblance, albeit on a smaller scale, to the ZigZag Pass horseshoe on Bataan.41 Perhaps lessons had been learned from the 38th Division’s experience at the ZigZag; at any rate the 7th Cavalry did not attack until it had obtained a complete picture of the Japanese defenses from captured documents and patrol actions, napalm and artillery had laid bare the terrain at the sawmill, air and artillery bombardments had reduced the bulk of the defenses to rubble, and four artillery battalions were in position to provide extremely close support. The cavalry’s attack went well and overran the defenses by midafternoon, 9 May. The 7th Cavalry killed some 350 Japanese in the area from 7 through 9 May; almost all of the rest of the original 650 defenders of the sawmill area had been killed by the air and artillery bombardments. The 7th Cavalry lost 4 men killed and 17 wounded, and attached guerrillas lost 2 killed and 4 wounded.
Pausing only briefly to reorganize, the 7th Cavalry marched on up Route 455 and, leaving its vehicles behind, reached Lamon Bay on 13 May. LCMs of the 592nd Engineer Boat and Shore Regiment brought supplies and vehicles around the Bicol Peninsula to Lamon Bay in preparation for an attack on Infanta, the principal town on the bay’s shores. The engineers also transported a guerrilla battalion under Lt. Col. Bernard L. Anderson, USA, to the Infanta area. As the cavalrymen and guerrillas converged on the town the Japanese garrison, mainly naval troops, fled west into the Sierra Madre. Infanta fell on 25 May, and by evening the next day the reinforced 7th Cavalry had cleared the entire flat, rice-rich region around the town against scattered, ineffective resistance. Maintained by overwater supply movements, the 7th Cavalry instituted an intensive patrolling program. The 8th Cavalry, meanwhile, cleaned out the northern section of the Santa Maria Valley, patrolled north into the Sierra Madre, and maintained contact with the 112th Cavalry, which had replaced the 43rd Division in the region east from New Bosoboso and Antipolo.
From 31 March to the end of May operations against the Kogure Detachment and the Japanese naval forces in the Lamon Bay region cost the 103rd RCT, the 2nd Cavalry Brigade, and attached guerrillas – mainly Anderson’s Battalion – approximately 65 men killed and 180 wounded. The Japanese lost at least 1,250 men killed in ground action, while American air and artillery bombardments, as a conservative estimate, accounted for another 500 Japanese.
The End of the Shimbu Group
By the end of May the Shimbu Group was no longer an effective fighting force,
7th Cavalry at Kapatalan Sawmill
a fact that General Yokoyama had recognized when, on the 27th, he had ordered a general withdrawal all across his western front.42 The group still had a strength of nearly 26,000 men – over half its total as of 20 February – but the survivors were the dregs, for XI and XIV Corps had decimated the best-trained and best-equipped units. About 13,000 of the survivors were left in organized units, the combat effectiveness of which is worthy of mention only in passing. Of the other 13,000, around 5,000 were undergoing whatever medical treatment the Shimbu Group was capable of providing. The final 8,000 were neither controlled nor controllable, having broken up into small groups to forage for food or to try to make their way to northern Luzon.
The Shimbu Group’s supply picture at the end of May was even gloomier than its personnel picture. The group had been unable to transport into the Sierra Madre any significant part of the huge stockpiles of supplies it had brought out of Manila, and the only supplies it still had plenty of were ammunition for small arms and machine
guns and medical matériel employed in the treatment of combat wounds. Lack of food was the principal problem. The early loss – before the harvest – of the Bosoboso Valley, the shores of Laguna de Bay, the Santa Maria Valley, and the Infanta region had deprived the group of expected food stocks, while almost all the food brought out of Manila had already been consumed. The organized remnant of the Noguchi Force, for example, could issue only two ounces of rice per day to each man, and even that meager amount would be gone by mid- June. The Kobayashi Force was little better off; the Kawashima Force, was still able to issue 6-8 ounces of rice per day. Most troops were reduced to eating roots, bark, grass, and food scrounged from long-abandoned Filipino gardens. Needless to say there was not a Filipino pig, carabao, or dog left alive within the sight of the Shimbu Group remnants before many days of June had passed.
Recognizing that mere existence was the major problem, Yokoyama hoped to move his organized units into areas where they might have some chance to raise food, scattering them through the Sierra Madre. XI Corps, however, was not going to give Yokoyama much rest. General Hall directed the 38th Division to mount limited attacks eastward from the Wawa Dam area and attached to the division for this purpose the 2nd Provisional Regiment, East Central Luzon Guerrilla Area. Recently reorganized and re-equipped by XI Corps, the guerrillas were commanded by Maj. Edwin P. Ramsey, AUS, who had not surrendered back in 1942. The 43rd Division, the 112th Cavalry RCT, the 2nd Cavalry Brigade, and the Anderson Battalion would continue to patrol in the areas they already held.43
As operations evolved after 1 June, the 38th Division’s objective became Santa Iñez, at the end of the Shimbu Group supply road into the Sierra Madre northeast of New Bosoboso.44 The 112th Cavalry RCT, employing mountain and river valley trails, mounted a converging attack toward Santa Iñez from the south, taking the town against light opposition on 9 June. The Japanese defended more stubbornly against the 151st Infantry, 38th Division, which drove toward Santa Iñez along the road from New Bosoboso, and the 151st was unable to make contact with the 112th Cavalry until 18 June. Meanwhile, other troops of the 38th Division, and the 169th Infantry of the 43rd Division as well, slowly pressed east into the mountains from the Wawa Dam area. By the end of June the only evidence of organized Japanese resistance in an area five miles north and ten miles east of Wawa Dam was confined to the Lenatin River valley about three miles north of Santa Iñez, the region into which Shimbu
Group headquarters had withdrawn. North and east of Ipo Dam, 43rd Division patrols found no signs of organized resistance. The 2nd Cavalry Brigade in the Santa Maria Valley-Infanta area, dispersed the last organized remnants of the Kogure Detachment and the Japanese naval units at Lamon Bay.
There was no dramatic conclusion to XI Corps’ mopping-up operations during June. Instead, the corps pulled its regular units out of the mountains to wet-weather camps for rest and rehabilitation in preparation for the invasion of Japan, while guerrilla units, reorganized and re-equipped, took over the task of hunting down Japanese stragglers. During June XI Corps had projected its strength into the Santa Iñez area – the very center of a region that General Yokoyama had expected to hold more or less indefinitely – forcing the Shimbu Group remnants into trackless, partially unexplored wilderness. Its June operations had cost XI Corps roughly 110 men killed and 370 wounded, including approximately 35 killed and 75 wounded among attached guerrilla units. Japanese losses during the month were 7,540 killed or found dead and 1,105 captured.
Certain tactical innovations of the June mop-up period merit special attention. First, the 38th Division made extensive use of antiaircraft searchlights to illuminate its front lines at night. Begun during the last stages of the division’s drive to Wawa Dam in May, night illumination was brought nearly to the status of an exact science during June. Another innovation, subsequently to see far-reaching development, was the employment of helicopters. In the 112th Cavalry RCT and the 38th Division sectors helicopters evacuated sick and wounded from inaccessible mountain positions, obviating the need for dangerous and tiring hand-carry evacuations that often consumed as much as twenty-four hours. Finally, in late May and throughout June troops of the 38th and 43rd Division combat-tested 57-mm. and 75-mm. recoilless rifles and 4.2-inch recoilless mortars. The troops, who wanted many of the weapons immediately, enthusiastically praised the new 57-mm. and 75-mm. weapons, later to see much development, but supplies of the rifles were so limited that no distribution could be made. The recoilless mortar, on the other hand, proved unsatisfactory. It was inaccurate, of limited mobility, and very difficult to emplace because it required such a large clearance zone to its rear.
At the end of June the Shimbu Group remnants were in sorry shape, and almost all of its elements had broken up into small parties concerned primarily with a hunt for food.45 During June the group had lost three men dead of starvation or disease to every one man killed in combat, and before July was over the ratio had mounted to nearly ten to one. U.S. Army estimates of Shimbu Group strength as of 30 June varied from 3,300 to 6,500,46 but General Yokoyama actually had nearly 15,000 troops under his nominal command.
The 149th and 151st Infantry Regiments, 38th Division, aided by almost 10,000 guerrillas, continued to operate
in the Shimbu area until the end of the war. Each regiment rotated battalions into the mountains, but the battalions largely confined their activities to support and control of guerrilla units. By mid-August 1945 the Fil-American forces had killed, found dead, or captured another 5,000 Japanese in the Shimbu Group’s mountain retreat. After the end of the war approximately 6,300 Shimbu survivors surrendered. With 2,000 prisoners captured before September 1945, these were all that remained alive of Yokoyama’s original 50,000 troops.47