The Japanese are ascendant as they successfully invade the East Indies, Singapore and the Philippines. But, in March 1942, the Americans get their first taste of victory at the Battle of the Coral Sea, a result of finally cracking the Japanese codes.
Then at the Battle of Midway, the fate of the Japanese was sealed. The Japanese strike force attempted a landing on the island of Midway. The Americans were ready and Admiral Spruance's fleet sunk all four Japanese carriers, the same ones that were used for the attack on Pearl Harbor. The Imperial Fleet was forced to retreat, never to go on the offensive again.