How did the Americans learn about the Japanese plan to attack on Midway Island?

After a sudden multiple attack on Aleutian Islands and off the coast of Alaska, Japanese planned a prolonged attack towards Midway.

Explanation:

Japan's aim was to prove its superiority over naval and air force of America firstly it attacked Aleutian islands and off the coast of Alaska. Thereafter they planned for a prolonged attack on America. But from their previous sudden attack America got to know about their future plan.

U. S navy defeated Japan's sudden attack and won the battle of midway. To protect women's role it was important to America to combat Japan and defeat them in the midway battle.