The ship in the photo is USS General R. E. Callan, AP-139. "AP" = "transport". She's a General G. O. Squier class transport, built in Richmond, California, in 1943-1944, launched in 1944, and commissioned 17th August, 1944. She was named after US Army General Robert Emmet Callan, an artillery officer who served in the Spanish-American War, and went on to serve as Chief of Staff of the 1st Army Artillery and commander of the 33rd Artillery Brigade in WWI.
She spent the end of 1944 and the first half of 1945 taking troops to-and-fro to New Guinea, Hawaii, Guam, Australia, and India and Ceylon (Sri Lanka), and then moved to the Atlantic to do similar work after VE-Day, bringing soldiers back from France, and then from India after VJ-Day, and then once more across the Atlantic and continuing around the world across the Indian and Pacific oceans back to the west coast.
She went on to Boston, where she was handed over to the Army for use as a transport on 24th May, 1946. She worked as an Army transport as USAT General R. E. Callan until 1950. In mid-1949, the US Department of Defense rationalised its maritime transport services, establishing the Military Sea Transport Service (MSTS) to serve the needs of all the branches of the US armed forces, still in operation today as the Military Sealift Command (MSC). The core of the MSTS is ships owned by the Navy, but not commisioned in the Navy, and mostly manned by civilians; these ships are augmented by chartered civilian ships. Serving with MSTS as USNS General R. E. Callan, T-AP-139, she supported US forces in Europe until 1958, when she was removed from service and joined the National Defense Reserve Fleet.
This was not the end of her career. In 1961 she was handed over to the Air Force, and refitted as a Missile Range Instrumentation Ship (AKA range ship), and served the Air Force in this role as USAFS General H. H. Arnold (perhaps the Air Force didn't want her to be named after an Army artillery general). She returned to MSTS, and Navy ownership, still in the same role, as USNS General H. H. Arnold, T-AGM-9. She served until 1982, when she was removed from Navy service in January, and sold for scrapping in October.
For more on her and her career: