By May 1942 the Japanese had swept all before them, decimating the American surface fleet at Pearl Harbor, supporting a succession of amphibious attacks on the Philippines and Indonesian archipelago, and even penetrating into the Indian Ocean. Their next step was the occupation of Port Moresby on Papua New Guinea, a stone's throw from the Australian coast. The Battle of the Coral Sea was the first check in this triumphal progress. Strategically, it caused the invasion fleet to withdraw: the high-water mark of Japanese success had been reached. Tactically, it demonstrated that Japanese pilots were not invincible, that they could be stopped by an aggressive use of naval airpower, and that the U.S. Navy could do this. The Battle of the Coral Sea was the first true carrier battle, and both commanders rewrote the rulebooks as they showed how carriers would become the dominant feature of naval warfare.