immediately began preparing a new plan, which was based on a preliminary draft by Admiral Koga, the plan became known as A-GO. A-GO envisioned a decisive fleet action, where the areas for the decisive battle were deemed to be the Palaus and the Western Carolines. It was in these areas that the Mobile Fleet, along with large numbers of land-based aircraft, would be concentrated. If the Americans attacked the Marianas, they would be attacked by land-based planes in that vicinity. Then the Americans would be lured into the areas where the Mobile Fleet could defeat them. A month after Koga's death, Admiral Soemu Toyoda become the new commander of Combined Fleet. Philippine Sea An opportunity for a decisive battle came in June 1944, when the Americans landed on Saipan in the Marianas. The Japanese responded with their largest carrier force of the war, the nine-carrier Mobile Fleet, led by Shōkaku, Zuikaku, and the new armored-deck aircraft carrier . The resulting clash, the largest carrier battle in history, did not turn out as the Japanese had hoped. Instead, it ended in near-total defeat and the virtual end of their carrier force. On June 19, a series of Japanese carrier air strikes were shattered by strong American defenses. The same day, Shōkaku was hit by four torpedoes from the submarine and sank with heavy loss of life. The Taihō was also sunk due to a single torpedo hit from the submarine . Late the next day, the Japanese were subjected to American carrier air attack, suffering the loss of several ships, including the carrier Hiyō. The four Japanese air strikes had involved 373 carrier aircraft, of which only 130 returned. More aircraft and their crews were lost when Taihō and Shōkaku were sunk by American submarines. After the second day of the battle, Japanese losses were 3,000 dead, three carriers, two fleet oilers, more than 400 carrier aircraft, and around 200 land-based aircraft, plus damage to several ships. The Americans lost 109 dead, 123 aircraft (80 of which ran out of fuel returning from the strike on the Japanese fleet), and bomb damage to the battleship South Dakota. Although this defeat was severe in terms of the loss of the fleet carriers Taihō, Shōkaku, and Hiyō, the real disaster was the annihilation of the carrier air groups. These losses to the already-outnumbered Japanese were irreplaceable. The Japanese had spent the better part