The Marianas chain of islands, consisting primarily of Saipan, Tinian, and Guam, were considered as being ideal bases from which to launch B-29 Superfortress operations against Japan. The islands were about 1500 miles from Tokyo, a range which the B-29s could just about manage. Most important of all, they could be put on a direct supply line from the United States by ship. The XXI Bombardment Command had been assigned the overall responsibility of the B-29 operations out of the Marianas bases.