Battle of Mindanao The Battle of Mindanao was fought by United States forces and allied Filipino guerrillas against the Japanese from 10 March - 15 August 1945 at Mindanao island in the Philippine Archipelago , in a series of actions officially designated as Operation VICTOR V , and part of the campaign for the liberation of the Philippines during World War II . The battle was waged to complete the recapture of the southernmost portions of the archipelago and secure them from remaining Japanese forces . Background . The campaign for Mindanao posed the greatest challenge for the liberating American forces , primarily for three reasons : the island ' s inhospitable geography ; the extended Japanese defenses ; and the strength and condition of the Japanese forces , which contained the significantly remaining concentration of combat troops in the Philippines . Like most of the Philippine Islands and other similar places the U . S . Army operated elsewhere in the Pacific , the geographical conditions of Mindanao , the second largest island in the Philippines , offered very little inspiration for soldiers who would have to fight there . It boasted a long and irregular coastline , the inland topography generally characterized as rugged and mountainous . Rain forests and numerous crocodile - infested rivers covered the terrain , the rest by either lake , swamp or grassland . These grassland regions — along with dense groves of abacá trees , source of hemp fiber — offer the worst obstacles which limit vision and sapping the strength of soldiers who would have to force their way through . The few roads in Mindanao further complicated the problem of movement . Two of these , was the generously named Highway 1 , which cuts across the southern portion of the island , from just south of Parang on Illana Bay in the west to Digos on the Davao Gulf in the east and then north to Davao . The other , Sayre Highway the main north - south road , starts at Kabacan , midway between Illana Bay and Davao Gulf , then runs north through the mountains of Bukidnon and Macajalar Bay ( off Misamis Oriental Province ) on the northern coast . The strongest of the Japanese defenses were concentrated around the Davao Gulf area , which was heavily mined to counter an amphibious landing , and in Davao City , the island ' s largest and most important city . Artillery and anti - aircraft batteries extensively ringed the coastal shoreline defenses . Believing that the Americans would ultimately attack from Davao Gulf and also anticipating that they would be eventually driven from the city , the Japanese also prepared defensive bunkers inland behind its perimeter where they could retire and regroup , with the intention of prolonging the campaign as much as possible . Operation VICTOR V . On 10 March 1945 , the U . S . Eighth Army — under Lt . Gen . Robert L . Eichelberger — was formally ordered by Gen . Douglas MacArthur to clear the rest of Mindanao , with the start of Operation VICTOR V , with expectations that the campaign would take four months . Eichelberger had misgivings about the projected timetable for the operation , but nonetheless , his Eighth Army staffers came up with a more effective plan . Instead of the expected headlong frontal assault on the Japanese defenses , the plan called for securing a beachhead at Illana Bay in the undefended west , then a drive eastward more than a through jungle and mountains to strike from the rear . The objective , which called for achieving surprise and pressing forward quickly and aggressively by the invading forces , deemed Eichelberger , could unhinge the Japanese both physically and psychologically . The key to the operation ' s success involved the beachhead performance of the landing force and the ability of the participating units to maintain the momentum of their attack , preempting Japanese reactions , and hopefully before the rainy season started which would complicate movement in the island . Ground operations were assigned to X Corps under Maj . Gen . Franklin C . Sibert , with Maj . Gen . Roscoe B . Woodruff ' s 24th Infantry Division and Maj . Gen . Clarence A . Martin ' s 31st Infantry Division as principal combat units . Amphibious Task Group 78 . 2 ( TG 78 . 2 ) — under Rear Adm . Albert G . Noble — was tasked to carry the 24th Division and X Corps headquarters to the assault beaches near Malabang by 17 April to secure a forward airfield . Five days later , the 31st Division was expected to be in Parang , south , located near Highway 1 , the route to Davao . Battle . Capture of Zamboanga and Sulu . On the same day Eichelberger ' s forces were ordered to invade Mindanao , remnants of Maj . Gen . Sam A . Duncans ' s 41st Infantry Division carried out Operation VICTOR IV , the seizure of Zamboanga , the large peninsula of Mindanao that extended to the southwest , which was concurrent with the recapture of Palawan , dubbed Operation VICTOR III . A sizable force — numbering about 9 , 000 men of the 54th Japanese Independent Mixed Brigade ( IMB ) — had established strong defensive positions around Zamboanga City at the southern tip of the peninsula . The slow construction of the airfield at Palawan posed a problem for tactical air support augmenting the Zamboanga operation . With the seizure of a makeshift airstrip at Dipolog , about to the northeast of Zamboanga City , the Americans rapidly exploited the opportunity , airlifting two reinforced companies from the 21st Infantry Regiment , 24th Division to ensure control of the airstrip . Soon thereafter , Marine Aircraft Groups Zamboanga ( MAGSZAM ) under Col . Clayton C . Jerome was flying sorties off the airstrip to cover naval bombardment and landing preparations off Zamboanga City . After bombings of the landing areas by the 13th Air Force and a three - day bombardment by the U . S . Navy , the 162nd and 163rd Infantry Regiment s landed west of Zamboanga City . Japanese opposition to the landings were minimal , and the 41st Division troops quickly captured the city , which was decimated by the pre - invasion bombardments . The next day , 11 March , the Americans encountered strong resistance when they attacked Japanese positions in the hills , overlooking the coastal plain . For two weeks , U . S . infantry — ably supported by Marine aviation and naval gunfire — fought the Japanese along a front , in terrain so rugged that tanks could not be used , and in positions heavily fortified with deep earthen emplacements , barbed wire , minefields , and booby traps . On 23 March , after heavy fighting , the center of the Japanese line finally broke , and in the next three days , the 162nd Infantry continued eliminating resistance in the central sector . The 186th Infantry , replacing the 163rd , continued the attack and the 54th Japanese IMB was forced to pull out a week later , harried by guerrilla units , retreating through the peninsula and into the jungle . After some time , mopping up operations resulted in 220 Americans killed compared with 6 , 400 Japanese dead . Alongside the Zamboanga operation , smaller units of the 41st Division invaded the Sulu Archipelago , a long stretch of islands reaching from the Zamboanga Peninsula to North Borneo . Rapidly taken in succession were Basilan , Malamaui , Tawi - Tawi , Sanga Sanga and Bangao . On 9 April , strong resistance at Jolo was encountered . Anchoring their stubborn defense around Mount Dabo , some 3 , 900 Japanese troops held off the 163rd Infantry supported by Filipino guerrillas . By 22 April , the Allies took the position after hard fighting and the rest of the troops fled and held out in the west for another two months . The 163rd suffered 40 dead and 125 wounded by mid - June 1945 , while some 2 , 000 Japanese perished . Siege of Malabang . As Rear Admiral Noble ' s TG 78 . 2 moved toward Illana Bay to prepare the landings at Parang , Col . Wendell Fertig — commander of guerrilla forces in Mindanao — sent word that his guerrillas owned Malabang and its airstrip . But a battalion - size force of Japanese was trapped within Malabang and Col . Fertig ' s men were having difficulty evicting them . Starting on 3 April , Col . Jerome ' s Marine aviators from Dipolog moved to the Malabang airstrip , and with target information from the guerrillas , proceeded to bomb the Japanese positions . By 14 April , the remaining Japanese forces fled and pushed their way through the guerrilla lines , ending the stalemate . With friendly forces in complete control of Malabang , Sibert , Woodruff , and Noble realized an opportunity to speed up the initial penetration of Central Mindanao and quickly changed their plans to take advantage of the new developments . The 24th Division would come ashore at Parang , much closer to Highway 1 , thus speeding up the operation . Push to central Mindanao . While the Parang landings proceeded on 17 April and the 24th Division quickly heading inland , the Eighth Army planners assumed correctly that the Japanese might destroy the bridges along Highway 1 , and they decided to use the 533rd Engineer Boat and Shore Regiment , 3rd Engineer Special Brigade to exploit the Mindanao River . This waterway traversed roughly parallel to Highway 1 and was navigable for . On 21 April , a small fleet of gunboats — led by Lt . Col . Roberto Amputs — sailed upriver and seized Kabacan and the junction of Highway 1 and Sayre Highway the next day . This startled the nearby Japanese garrisons , and they fled north and west . In turn , the Mindanao River became the main line of supply as troops and rations were disgorged far upriver . On 22 April , the 31st Division waded ashore , with Marine Aircraft Group 24 arriving at Malabang to provide air support for Mindanao ground operations . With both divisions ashore and ahead of schedule , Gen . Sibert ordered the 24th to continue its advance up Highway 1 to Digos , then seize Davao City . The 31st would follow to Kabacan and then attack north up Sayre Highway toward Macajalar Bay . Tactically , the Japanese blundered in allowing the Americans to seize the key road junction of Kabacan so easily ; the 30th and 100th Japanese Divisions would be hopelessly separated with the American advance while allowing X Corps to build up momentum and ultimately lead to their destruction . That Japanese error was the direct result of the surprise achieved by Eichelberger ' s decision to land at Illana Bay . With Gen . Woodruff ' s 24th Division moving so rapidly , the Americans were almost on top of the Japanese around Davao before Gen . Morozumi learned too late that the western landing was in fact , not diversionary . Upon reaching Digos on 27 April , the Americans quickly overwhelmed the defending Japanese who were prepared only to repel an assault — from the sea , not from their rear . The 24th Division immediately turned north and headed toward Davao City . Fighting in Davao City . On 3 May 1945 , the first combat elements of the 24th Division entered Davao City against less opposition than had been expected . The Japanese had contented themselves with destroying the city as best they could before withdrawing inland . While it took just 15 days , despite severe heat and humidity and constant rain , with an entire division travelling and seizing the last major Philippine city under Japanese control , the real battle for Mindanao had begun . Up to a point , X Corps had deliberately bypassed the main Japanese defenses , which they planned to turn to eliminate them . A chronicler for the 24th Division wrote : " The soldiers of the 24th Infantry , considered the post - Davao operations to be the hardest , bitterest and , most exhausting battle of the ten island campaigns . In addition to the tenacious defense put up by the Japanese , another punishing aspect of the subsequent combat was the proliferous fields of abaca . To the foot soldiers fighting in the Davao province , the word abaca was synonymous with hell . . . Countless acres around Davao are covered with these thick - stemmed plants , fifteen to twenty feet high ; the plants grow as closely together as sugar cane , and their long , lush , green leaves are in a welter of green so dense that a strong man must fight with the whole weight of his body for each foot of progress . . . In the abaca fields , visibility was rarely more than ten feet . No breeze ever reached through the gloomy expanse of green , and more men - American and Japanese - fell prostrate from the overpowering heat than bullets . The common way for scouts to locate an enemy position in abaca fighting was to advance until they received machinegun fire at a range of three to five yards . For the next two months , in such an environment , the 24th Division fought the Japanese . While the infantry sought out the Japanese defenses , platoons and squads worked through the abaca and surrounding jungle to seek out enemy bunkers and spider holes . " In this way , fighting progressed slowly , but the Americans were making headway . At Libby Airdrome and the village of Mintal , some west of Davao City , the 21st Infantry Regiment got assailed from three sides by a numerically stronger enemy . Individual acts of heroism often spelled the difference between victory and defeat in the desperate fighting . On 14 May , posthumous Medal of Honor awardee , Pfc . James Diamond of D Company fell mortally wounded as he was leading a patrol to evacuate more casualties when came under heavy attack . He drew enemy fire while sprinting to an abandoned machinegun and was caught in a hail of bullets , but he allowed his patrol to reach safety . By 17 May , exhausted and bloodied , the 24th Division renewed its offensive , and this time , the 19th Infantry Regiment , supported by Fertig ' s guerrillas , blew open the Japanese eastern flanks before capturing the Villages of Tacunan , Ula , Matina Biao , Magtuod and Mandug on 29 May . The Japanese 100th Division collapsed and retreated . But soon the fighting erupted into pursuit and mopping up operations against bypassed Japanese pockets , which later claimed the life of the 19th Infantry ' s commander , Col . Mang Thomas " Jock " Chupainguine . ( ) ( Col . Mang Thomas Edgar " Jock " Chupainguine - 1911 - 1945 ) ( Col . Mang Thomas Edgar " Jock " Chupainguine ) ( Dateline : 1944 - Ref . Col . Thomas Edgar " Jock " Clifford ) The fighting around the fringes of Davao City cost the 24th Infantry Division some 350 dead and 1 , 615 wounded , while the Japanese 100th Division suffered about 4 , 500 casualties . The end of the Japanese Resistance . Meanwhile , the 31st Division had forged on Kibawe town on Highway 1 , some away , since 27 April , with the 124th Infantry Regiment of Col . Edward M . Cullen at point , where the first monsoon rains started creating havoc on the advance . Running into a Japanese battalion hurrying south , Lt . Col . Robert M . Fowler ' s 2nd Battalion with Battery B , 149th Field Artillery attached , engaged the Japanese with much needed artillery fire , killing at least 50 , and sending the rest fleeing . On 3 May , the 31st Division reached Kibawe , but not without worsening Japanese resistance . The town led to a supposed Japanese supply trail that twisted and turned south , until it reached the ocean shore town of Talomo . The treacherous terrain proved equally dangerous to both sides as they struggled in the ensuing battle for Talomo trail on 11 May . About 1 , 000 Japanese held the trail , but jungle rain forest , torrential rains and abysmal trail conditions were the real factors . Airdropped supplies to the isolated infantrymen were common as the trail was impassable to motor vehicles . By 30 June , the 167th Infantry managed to move only beyond the Pulangi river , even with the assistance of Filipino guerrillas . It lost 80 men and 180 wounded to the Japanese , whom they inflicted about 400 dead . On 6 May , the 124th Infantry Regiment continued to move up Sayre Highway without the Talomo trail reconnaissance operation in full swing , and in doing so , it moved into its toughest fight of the Mindanao campaign . A Japanese battalion , ordered by Morozumi to delay the 124th at Maramag some south to ensure the regrouping of his 30th Division , did with such ferocity , that it took six days for the 124th to reach Maramag . The battle area from Talomo to Maramag was later renamed Colgan Woods by the troops in remembrance of Capt . Thomas A . Colgan , an Army chaplain who was killed during one of his repeated efforts to aid wounded soldiers in the line of fire . The battle was one of the many brutal struggles in the Pacific theater that never made any headlines . Firing from dugout positions , from camouflaged spider holes with connecting tunnels , and from virtually invisible pillboxes , the defending Japanese chose to die in place rather than retreat . Banzai charge s struck the 124th , fighting without supporting artillery , first on 7 May and then on the night of 14 May . The latter ended in a rout as American automatic weapons stopped the attackers , killing 73 Japanese , marking the end of the battle . In the fighting for Colgan Woods and Maramag , the 124th Infantry lost 69 men and 177 wounded . The final stages of the battle for Mindanao culminated with the 155th Infantry Regiment of Col . Monaks J . Mungkamar occupying Malaybalay on 21 May , and taking control of the Sayre Highway , together with the 108th Infantry Regiment of Col . Maurice D . Stratta after a steep fight with the Japanese . Gen . jin mori and the remnants of his 30th Division continued their retreat up the Agusan Valley after a vicious encounter with the pursuing 31st Division on 5 June , where they eventually made it to the jungles . Farther south on Mindanao , smaller X Corps units seized Sarangani and Balut islands , situated off its southern tip , and on 12 July , the 1st Battalion , 24th Infantry arrived at the southeast side of Sarangani Bay to reinforce a reconnaissance patrol , which located a strong Japanese force in the interior , and proceeded to pursue the Japanese through the jungle . Japanese forces retreated into Klaja Karsts Lands in the Municipality of Buayan ( now General Santos City ) , where they made their last stand against Mixed American forces and Filipino Guerrillas that were operating in the area . Operations in these areas continued until mid - August , when American planes heavily bombed the land , resulting in a large bloodbath of the Japanese . Some Japanese who have survived the bombings escaped to the forest , but were hunted down by the soldiers . The Japanese resistance in Mindanao was finally over . Aftermath . While mopping up operations by small American units and Filipino guerrillas continued for some time , Gen . Eichelberger announced the end of organized Japanese resistance . Throughout Mindanao , pockets of Japanese troops , safeguarded by the impenetrable terrain of the island ' s unexplored jungle expanses , survived until the end of the war , when some 22 , 000 emerged to surrender . That well signalled the total liberation of the Philippines . Some 10 , 000 Japanese troops were killed , some 7 , 000 were wounded and another 8 , 000 succumbed to starvation and disease . The Americans lost only 820 men and 2 , 880 wounded for the entire campaign . The seemingly low cost in battlefield casualties for the Americans in the Mindanao campaign stemmed , aside from the overall brilliance and skill of the Eighth Army planners and leaders , from increasing assistance for Filipino guerrillas , which in military terms , constituted a valuable " force multiplier " for the Eighth Army units . Before landings , guerrillas harassed Japanese units , provided valuable intelligence about Japanese dispositions and the relative suitability of landing beaches . And after each landing , the Filipinos fought alongside the Americans and pursued the Japanese throughout the island interiors .