After the large American carrier air attack on the large Japanese base at Truk (Operation Hailstone) in 1944, Admiral Hara was assigned to replace Admiral Masami Kobayashi as the commanding officer of the Japanese "4th Fleet", though he actually commanded the land base at Truk with no warships assigned to him. Truk was left behind by the U.S. Navy in a rear area to "wither on the vine" in isolation, rather than being invaded and occupied. (This was the fate of many Japanese bases on Pacific islands, including the large one at Rabaul and several on New Guinea.) Admiral Hara was trapped at Truk without reinforcements or fresh supplies all the way through the final surrender of Japan on September 2, 1945.