Tag: shimbu-group

Definition

The Battle of Wawa Dam (February 20 – May 31, 1945) was the fight by which Lieutenant General Walter Krueger’s Sixth United States Army reduced the Shimbu Group’s mountain positions east of Manila and seized the Wawa Dam on the Marikina River at Montalban — today Rodriguez, Rizal — the standard account calls it the longest continuous combat of the liberation of the Philippines. The attackers were two corps in succession: XIV Corps under Major General Oscar Griswold opened the drive east across the Marikina in late February with the 1st Cavalry and 6th Infantry Divisions, and “late on 14 March General Hall, commanding XI Corps, took over responsibility for the conduct of operations against the Shimbu Group” — Major General Charles P. Hall’s corps, this wiki’s XI Corps entry carries it, with the Wikipedia article dating XIV Corps’ reassignment south to March 15 — closing the battle through May with the 6th, 43rd, 37th, and 38th Infantry Divisions, the 112th Cavalry Regimental Combat Team, and the Marking and Hunters ROTC guerrillas. (Wikipedia — Battle of Wawa Dam, CMH — Triumph in the Philippines, Ch. XXI)

The defenders were Lieutenant General Shizuo Yokoyama’s Shimbu Group — the 80,000-man southern-Luzon command this wiki’s Shimbu Group entry documents, roughly 30,000 on the east-Manila front, built on the 8th Division, the 39th Independent Mixed Brigade, and the 65th Independent Infantry Brigade and deployed operationally as the Kobayashi Force of some 12,000 between Wawa Dam and Antipolo, the Kawashima Force of about 9,000 on the Ipo Dam front, and the Noguchi Force of roughly 9,000 south of Antipolo. Water logic drove everything: Ipo Dam supplied a third of Manila’s water, Novaliches Reservoir half the city’s needs at best, and Wawa Dam — abandoned as a Manila source after 1938 — only some 15 percent, a fact unknown to MacArthur’s headquarters in April 1945 when rationing had begun. The outcome: the 149th Infantry, 38th Division, secured the dam intact on May 28; General William C. Chase reported the sector “completely secured” on May 31 and the Kobayashi Force “practically eliminated” — at a cost of roughly 315 Americans and Filipinos killed and 1,010 wounded against about 7,000 Japanese dead. (CMH — Triumph in the Philippines, Ch. XXI, CMH — Triumph in the Philippines, Ch. XXII, Wikipedia — Shimbu Group, Wikipedia — Battle of Wawa Dam)

Identities

Also Known As

• The Wawa Dam operation
• The Antipolo–Wawa sector fighting
• The Reduction of the Shimbu Group — the U.S. Army official history’s phase title covering the campaign

Examples and Analogies

• A dam worth a battle it could not water: the attackers spent March and May 1945 taking an obsolete reservoir — abandoned as a source after 1938, capable of 15 percent of supply — while the real prize, Ipo Dam, lay behind the Kawashima Force. (CMH — Triumph in the Philippines, Ch. XXI)
• Cave-warfare arithmetic: progress east of Manila “measured its daily progress in feet” — the 1st Infantry at one point advancing “hardly 250 yards” — until napalm, tanks, and flamethrower tanks turned Woodpecker Ridge from siege into rout between May 21 and 25. (CMH — Triumph in the Philippines, Ch. XXI, Wikipedia — Battle of Wawa Dam)
• Two corps, one front: XIV Corps opened the east-front drive, XI Corps closed it — the handover of March 14–15, 1945 is the battle’s hinge, matching this wiki’s entries on XI Corps and Oscar Griswold. (CMH — Triumph in the Philippines, Ch. XXI, Wikipedia — Battle of Wawa Dam)
• The cavalry that held the shoulder: the 112th Cavalry RCT — the regiment that had fought the Driniumor River at Aitape — held Baldy Force’s front north of Mount Oro while the infantry divisions took the ridge line and the dam. (CMH — Triumph in the Philippines, Ch. XXII)

Usage Scenarios

1. Studying the Liberation of Luzon East of Manila

The east-front counterpart of the Manila and Bataan operations this wiki’s Battle of Luzon and ZigZag Pass entries carry — five months of continuous combat after Intramuros fell, clearing Antipolo, San Mateo, Montalban, and Tanay. (Wikipedia — Battle of Wawa Dam, CMH — Triumph in the Philippines, Ch. XXI)

2. Analyzing Joint and Combined Operations

Air-ground integration at its most violent — Fifth Air Force and 1st Marine Aircraft Wing napalm “skip bombing” against cave positions, capped by the May 17, 1945 Ipo Dam strike the standard account calls the largest napalm bombing of the Pacific War — plus the integration of Filipino guerrillas. (Wikipedia — Battle of Wawa Dam, CMH — Triumph in the Philippines, Ch. XXII)

3. Military Geography of Manila’s Water System

The reference case for the capital’s water works as an operational objective: Novaliches and Balara secured February 6–7, a saboteur’s valve destroyed February 11, Ipo Dam the lifeline, Wawa the obsolete but fought-over objective. (Wikipedia — Battle of Wawa Dam, CMH — Triumph in the Philippines, Ch. XXI)

4. Battlefield Heritage and Local History

The surviving dam, gorge, and mountains of what is now Rodriguez, Rizal — the terrain this wiki’s Marikina River and Rodriguez, Rizal entries describe — remain the battle’s visible monument. (Wikipedia — Battle of Wawa Dam)

Strategies

• Turn the left first: Hall’s XI Corps concentrated against the Noguchi Force south of Antipolo, then swung north against Kobayashi and finally Kawashima — why Antipolo (taken by the 103rd Infantry on March 12) preceded the dam by more than two months. (CMH — Triumph in the Philippines, Ch. XXI)
• Let geography set the objective: Krueger’s orders to seize Wawa first and Ipo second rested on a false premise — the 1938 supersession — a standing lesson in verifying infrastructure intelligence before committing divisions to it. (CMH — Triumph in the Philippines, Ch. XXI)
• Task-organize freely: the 145th Infantry crossed from the 37th to the 38th Division for the final drive, and the 112th Cavalry fought as Baldy Force under its own commander, Brigadier General Julian W. Cunningham. (CMH — Triumph in the Philippines, Ch. XXII)
• Economize with firepower: napalm skip-bombing and armored flamethrowers substituted for infantry assaults on cave positions after March’s seesaw casualties, collapsing Woodpecker Ridge by late May. (CMH — Triumph in the Philippines, Ch. XXII, Wikipedia — Battle of Wawa Dam)

Security and Safety Measures

• Critical-infrastructure protection: the February 6–7 seizure of Novaliches and Balara, and the February 11 destruction of a valve by saboteurs, made the campaign an early case of water-works security in urban warfare — the danger that “severe epidemics might break out” drove the timetable as much as the enemy did. (Wikipedia — Battle of Wawa Dam, CMH — Triumph in the Philippines, Ch. XXII)
• Cave and tunnel clearing doctrine: napalm against entrances, tanks and flamethrower tanks against ridgeline positions, patient sealing rather than frontal assault. (CMH — Triumph in the Philippines, Ch. XXII)
• Flank and rear security: the 112th Cavalry’s Baldy Force north of Mount Oro guarded XI Corps’ line of communications throughout. (CMH — Triumph in the Philippines, Ch. XXI, CMH — Triumph in the Philippines, Ch. XXII)
• Surrender and mopping-up management: the fighting did not end with the withdrawal order — June operations killed or found 7,540 Japanese dead and took 1,105 prisoners, and Yokoyama surrendered the survivors, some 6,500 men, at Montalban on September 8, 1945. (CMH — Triumph in the Philippines, Ch. XXII, Wikipedia — Shimbu Group)

Historical Context

The battle grew out of Yamashita’s decision not to defend Manila: from December 17, 1944 Yokoyama’s Shimbu Group was made “wholly responsible for the defense of southern Luzon, from Manila southwards,” digging its western front into the Antipolo–Montalban mountains where the Marikina River forces its gorge at Wawa — directly above the capital’s water supply. XIV Corps attacked east on February 20–21, 1945, the 7th Cavalry fording the Marikina at Taytay and the 6th Division crossing on February 22, and fought a February–March campaign of feet and yards toward Antipolo: the 103rd Infantry occupied Antipolo on March 12, the same day Yokoyama’s counterattack collapsed before it began; on March 14 the 6th Division’s commander, Major General Edwin D. Patrick, was mortally wounded, Major General Charles Hurdis succeeding him; the next day the front passed to Hall’s XI Corps. (CMH — Triumph in the Philippines, Ch. XXI, Wikipedia — Shimbu Group)

XI Corps’ April–May grind broke the Kobayashi Force ridge by ridge: Mount Mataba’s crest on April 17, the 145th Infantry against Mount Pacawagan from April 21 to 30, the 38th Division’s May 4 offensive with Binacayan taken May 9 and Woodpecker Ridge cleared in the rout of May 22–25, while the 43rd Division and Marking’s guerrillas took Ipo Dam intact on May 17. Yokoyama ordered his general withdrawal on May 27; the 149th Infantry walked into Wawa Dam unopposed the morning of May 28 and found it intact; Chase declared the battle over on May 31. The June mop-up and the September 8, 1945 surrender at Montalban closed the campaign. (CMH — Triumph in the Philippines, Ch. XXII, Wikipedia — Battle of Wawa Dam, Wikipedia — Shimbu Group)

Challenges and Controversies

Which Corps Took the Dam — and the Record’s Other Frictions

Popular shorthand gives the battle to one corps or the other; the record gives it to both — XIV Corps broke the Shimbu left and took Antipolo, XI Corps took the dams — the handover dated “late on 14 March” in the official history and March 15 in the Wikipedia article. Similar frictions run through the sources: the Wikipedia infobox’s Japanese order of battle (“62nd Division,” a “Kawabuchi Force”) does not match the official history’s structure of the Kawashima, Kobayashi, and Noguchi Forces with the Kogure Detachment and the group reserve, and the Shimbu Group article’s component list (8th Division, 39th Independent Mixed Brigade, 65th Independent Infantry Brigade) must be reconciled with those operational “forces.” On contested points this entry follows the official history as primary, per house practice. (CMH — Triumph in the Philippines, Ch. XXI, Wikipedia — Battle of Wawa Dam, Wikipedia — Shimbu Group)

The Dam That Mattered Less Than Believed

The campaign’s premise — that Wawa Dam was a Manila lifeline — was false by seven years: superseded by Ipo Dam in 1938, Wawa could supply perhaps 15 percent of the city’s needs, and MacArthur’s April 18 cable on rationing took four days of clarification before Ipo became the priority. The battle is studied both as tactical success and as the intelligence failure that cost weeks of mountain combat. (CMH — Triumph in the Philippines, Ch. XXI, Wikipedia — Battle of Wawa Dam)

Remembered Roles versus the Record

The 112th Cavalry is widely remembered as “the regiment that took Wawa Dam”; the official history assigns it the northern shoulder as Baldy Force and gives the dam itself to the 149th Infantry, 38th Division — a distinction that matters to regimental history and to the battle’s commemoration in both American and Philippine accounts. (CMH — Triumph in the Philippines, Ch. XXII)

Related Topic

• Shimbu Group
• XI Corps
• Oscar Griswold
• Charles P. Hall
• Battle of Luzon
• Battle of Manila
• Battle of Ipo Dam
• ZigZag Pass
• 6th Infantry Division (United States)
• 38th Infantry Division (United States)
• 37th Infantry Division (United States)
• 1st Cavalry Division (United States)
• 112th Cavalry Regiment (United States)
• Marking Guerrillas
• Hunters ROTC
• Marikina River
• Rodriguez, Rizal
• Antipolo

References

1. Battle of Wawa Dam — Wikipedia
2. Triumph in the Philippines — Chapter XXI: The Reduction of the Shimbu Group, Phase I (U.S. Army CMH, HyperWar)
3. Triumph in the Philippines — Chapter XXII: The Reduction of the Shimbu Group, Phase II — The Seizure of Wawa and Ipo Dams (U.S. Army CMH, HyperWar)
4. Shimbu Group — Wikipedia