Like most Japanese naval planning during World War II, Yamamoto's battle plan was very complex. His was also based on incorrect (wrong) information. He thought that and were the only carriers available to the U.S. Pacific Fleet. In May 1942, during the Battle of the Coral Sea, had been sunk and so badly damaged that the Japanese thought she had been sunk. The Japanese also knew that was being repaired on the US West Coast after getting torpedo damage from a submarine. and were in the Atlantic, but the Japanese were not sure this was so.