The duty of protecting the southern and eastern flanks of Mindanao during the war in 1945 fell under Imperial Japanese Army Lt. Gen. Jiro Harada, leader of the 100th Division commander with control over the 75th Brigade, 76th Brigade, and the 32nd Special Base Force of Rear Adm. Naoji Doi. Its primary mission was to block the Allied Forces from entering Davao City.
Rear Adm. Doi (1894–1963) was a member of the 43rd Class of the Imperial Japanese Naval Academy. As an officer, he held three key military post in Mindanao. He was commander of the Rashin Area Special Base Force (June–September 1944), commander of the 32nd Special Base Force (October 1944–August 1945), and promoted to rear admiral on May 1, 1944. On the day Emperor Hirohito announced Japan’s surrender, his troops were hiding in the hills of Mandug.
Lt. Gen. Harada’s division was to defend Catigan, and the hills north of the city. The Right Sector Unit, composed of five infantry battalions, secured the west side of Davao River, while the Left Sector Unit, a party of two regular infantry battalions, two provisional battalions, and the poorly armed Air Force's Hosono Unit, took the east side. Another battalion aided as a reserve.
Robert Ross Smith, in Triumph in the Philippines, wrote: ’The Left District Unit dug in along rising ground overlooking Davao Gulf between Davao and Bunawan, twelve miles to the north, and held a series of outposts along Route 1 north of Davao. Admiral Doi's strongest–and last-stand–defenses were near Mandog, a hill barrio on the east bank of the Davao River seven miles north of the city. Doi's Hosono Unit took little part in subsequent operations, but hid out in hilly country ten miles northwest of Bunawan.’ Gen. Harada's eastern position was initially tested on May 29 when the U.S. 19th Infantry hit west toward Rear Adm. Doi's defenses at Mandug where the battlements were under threat. On June 9, Mandug was captured; days later, the last organized resistance in the area was reported.
To the general’s surprise, the 24th Division, which Lt. Gen. Harada expected to lead a frontal assault at the center, made no effort in mounting attacks against his flanks. Given this assessment, he moved two battalions from his flanks and transferred them to the highway sector where he focused most of his defenses. Still dissatisfied with his strong reserves, he took
an extensive shakeup of his units by transferring the majority of the Army ground combat forces from the east of Davao River to the west sector.
The U.S. 19th Infantry's mission, meanwhile, was focused on overrunning the Japanese defenses east of the river, including the destruction of Rear Adm. Doi's concentration in Mandug. The remnants of the Left District Unit, on the other hand, were forced to retreat to the north where it took shelter. In pursuit, the U.S. 34th Infantry punched toward the Davao River,
marking the collapse of the 100th Division's second line east at Ula.
On June 10, the 24th Division took over the 100th Division's second line from Wangan to Mandug. Already disheveled, the division hastily made a retreat to the mountains.
The job of annihilating Lt. Gen. Harada’s organized defenses cost the 24th Division about 350 men killed and 1,615 wounded while the 100th Division and its attached units lost roughly
4,500 men killed and 30 captured from April to June.
The Mandug conflict also delivered a hero in the last days of the mopping-up operations. On June 10, 1945, U.S. Staff Sgt. Elmer W. Alt, a member of the U.S. 19th Infantry, was felled by a
bullet while hunting Japanese remnants west of the city. His unit had just taken a hill overlooking the village, fighting all day to drive them until the attempt to retake the area was repulsed. Overall, the quest to liberate Davao City also produced two Medal of Honor awardees.
