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U.S. submarines accounted for 56% of the Japanese merchantmen sunk; mines or aircraft destroyed most of the rest. US submariners also claimed 28% of Japanese warships destroyed. Furthermore, they played important reconnaissance roles, as at the battles of the Philippine Sea (June 1944) and Leyte Gulf (October 1944) (and, coincidentally,[clarification needed] at Midway in June 1942), when they gave accurate and timely warning of the approach of the Japanese fleet. Submarines also rescued hundreds of downed fliers, including future U.S. president George H.W. Bush.

What was one of the important roles submarine played in the war?
reconnaissance roles