The U.S. Coast Guard PB-1G carried a droppable lifeboat. During the last year of World War II and shortly thereafter, the United States Navy acquired 48 ex-USAAF B-17s for patrol and air-sea rescue work. The first two ex-USAAF B-17s, a B-17F (later modified to B-17G standard) and a B-17G were obtained by the Navy for various development programs.[146] At first, these aircraft operated under their original USAAF designations, but on 31 July 1945 they were assigned the naval aircraft designation PB-1, a designation which had originally been used in 1925 for the Boeing Model 50 experimental flying boat.[154]