As Nagumo's bombers and fighters were taking off, 11 PBYs were leaving Midway to search for Japanese ships. They reported sighting two Japanese carriers with empty decks, which meant an air strike was on its way. American radar picked up the enemy at a distance of several miles, and planes were sent off to defend Midway. Bombers headed off to attack the Japanese carrier fleet. US fighters remained behind to defend Midway. At 06:20 Japanese carrier aircraft bombed and heavily damaged the U.S. base. Midway-based Marine fighter pilots, flying F4Fs and obsolescent F2As, intercepted the Japanese and had many losses. Most of the U.S. planes were shot down in the first few minutes; several were damaged, and only two could fly. In all, 3 F4Fs and 13 F2As were shot down. American anti-aircraft fire was accurate damaging many Japanese aircraft and destroying four.