For the April 1945 invasion of Okinawa, the Allies assembled the most powerful naval force in history. Since the few remaining capital ships of the Imperial Japanese Combined Fleet had been sunk or otherwise put out of action at the Battle of Leyte Gulf, the Allies were effectively unopposed in terms of major surface vessels; a single mission consisting of the superbattleship Yamato and a few escorts was undertaken, but the task force did not get within 200 nautical miles (370 km; 230 mi) of the invasion area. The main Japanese naval opposition within the invasion area came from hundreds of Imperial Japanese Navy Shin'yō-class suicide motorboats and Maru-Ni Imperial Japanese Army attack boats.