Final answer:
The decisive battle of World War II in the Pacific was the Battle of Midway, which shifted the balance of power towards the Allies.
Step-by-step explanation:
The decisive battle of World War II that became the turning point of the war in the Pacific was the Battle of Midway. This battle took place in June 1942 and resulted in a major victory for the United States. The US forces sank four Japanese aircraft carriers and defended their airfield on the small island of Midway. This victory shifted the balance of power towards the Allies and marked a significant setback for the Japanese navy.