U.S. forces executed landings on Guam and Tinian in July 1944 .

After heavy fighting , Saipan was secured Preventing_or_letting in July and Guam and Tinian in August 1944 .

The U.S. then constructed airfields on Saipan and Tinian where B-29s were based to conduct strategic bombing missions against the Japanese mainland until the end of World War II , including the nuclear attacks on Hiroshima and Nagasaki .