The United States Army Air Forces (USAAF) took delivery of its first B-24As in mid-1941. Over the next three years, B-24 squadrons deployed to all theaters of the war: African, European, China-Burma-India, the Anti-submarine Campaign, the Southwest Pacific Theater and the Pacific Theater. In the Pacific, to simplify logistics and to take advantage of its longer range, the B-24 (and its twin, the U.S. Navy PB4Y) was the chosen standard heavy bomber. By mid-1943, the shorter-range B-17 was phased out. The Liberators which had served early in the war in the Pacific continued the efforts from the Philippines, Australia, Espiritu Santo, Guadalcanal, Hawaii, and Midway Island. The Liberator peak overseas deployment was 45.5 bomb groups in June 1944. Additionally, the Liberator equipped a number of independent squadrons in a variety of special combat roles. The cargo versions, C-87 and C-109 tanker, further increased its overseas presence, especially in Asia in support of the XX Bomber Command air offensive against Japan.