Japanese air attacks on the Mariana Islands and anti-aircraft guns shot down about 37 Japanese aircraft during these raids. After the Marianas began to come under attack, the United States military stepped up its raids on the Japanese-held islands which could be used to launch raids on the B-29 bases. Particular attention was given to Iwo Jima, as it was correctly assumed that the Japanese aircraft which attacked the Marianas were flying from Japan and staging through the island en route to their targets. Following the first raid against Saipan in November, XXI Bomber Command B-29s were dispatched against Iwo Jima's airfields on November 5 and 8.
Japanese colonial empire provided convenient provisioning locations for ships. During the 1930s, the Imperial Japanese Navy began construction of airfields, fortifications, ports, and other military projects on the South Pacific Mandate islands, viewing them as "unsinkable aircraft carriers" with a critical role to play in the defense of the Japanese home islands against potential invasion by the United States. The islands became important staging grounds for Japanese air and naval offensives during the Pacific War, but were lost to American military action between 1943 and 1945. The League of Nations mandate was formally revoked by the United Nations on July 18, 1947 pusuant