From December 17, 1944, Lieutenant General Shizuo Yokoyama and his “Shimbu Group”, an independent detachment, were made wholly responsible for the defense of southern Luzon, from Manila southwards. The Shimbu Group was officially re-designated the Japanese 41st Army on March 6, 1945. Yokoyama commanded Japanese forces defending Manila against the U.S. Sixth and Eighth Armies. Following the Battle of Manila, Yokohama withdraw his surviving forces into the mountains of southern Luzon for a protracted guerrilla campaign, continuing to harass Allied forces until the surrender of Japan, by which time his army had been reduced to just 6500 men.