Answer:
Cracking Japanese codes to learn of their attack plans.
Explanation:
The Battle of the Coral Sea (May 1942) was the first air-sea battle of history. The Japanese planned to take control of the Coral Sea and prepared a landing in near Port Moresby in Papua New Guinea. Their communications had been intercepted because the American intelligence had broken the secret codes used by Japan. When the Japanese troops disembarked , they were attacked by American airplanes from the aircraft carriers.
The invasion was frustrated and this why it is considered an American victory.
