During the US invasion of Saipan in June 1944, Japanese troop ships attempting to reinforce the defenses were sunk by submarines. Shigenori Kami, chief of operations of the Navy Staff, volunteered to command "Yamashiro" to carry troops and equipment to Saipan. If the ship actually reached the island, he intended to deliberately beach the ship before it could be sunk and to use its artillery to defend the island. After Ryūnosuke Kusaka, Chief of Staff of the Combined Fleet, also volunteered to go, Prime Minister Hideki Tōjō approved the plan, known as Operation "Y-GO", but the operation was cancelled after the decisive defeat in the Battle of the Philippine Sea on 19 and 20 June.