Leroy Grumman's F4F Wildcat was not the fastest or most advanced fighter aircraft of World War II, but during the dark months after Pearl Harbor, Wildcat pilots stood firm, held the line, and stopped the Imperial Japanese military air forces when they seemed invincible. After war erupted in the Pacific, the Grumman F4F Wildcat was the primary fighter aircraft operated by the United States Navy and the Marine Corps. By 1942 every American Navy fighter squadron flew the F4F. Wildcat pilots encountered Japanese pilots flying the Mitsubishi A6M Zero (see NASM collection) more than any other enemy aircraft. The Zero could outmaneuver the F4F, but the Wildcat's heavy armament and solid construction gave it an advantage when flown by skilled pilots.