The major battle that marked a turning point in the Pacific Theater of World War II was the Battle of Midway, fought in June 1942. This decisive naval engagement resulted in a significant victory for U.S. forces against the Japanese fleet. It allowed the U.S. Navy to take the strategic initiative in the Pacific, shifting the balance of power away from Japan. The loss weakened Japanese offensive capabilities and set the stage for subsequent Allied victories in the core campaigns across the Pacific.