The Japanese knew their tiny volcanic island, Iwo Jima, would be attacked. Its crucial airfields lay only 650 miles from Tokyo, just over two hours flying time. So, under the command of LtGen Tadamichi Kuribayashi, Japan's best and brightest mining engineers turned remote Iwo Jima into a seemingly impregnable fortress. In the volcanic rock, laborers blasted out 16 miles of tunnels, connecting 1500 rooms. The engineers built underground hospitals and supply rooms under hundreds of feet of solid impenetrable rock. These were linked to over a thousand fortified artillery and anti-aircraft batteries, and machine gun and mortar bunkers. The Army Air Corps and Navy 16-inch guns pounded Iwo Jima in the longest sustained aerial offensive of the war; but the effect on the underground island fortress was negligible. Then on 19 February 1945 the Marines stormed the beach: 110,000 from 880 ships. The Japanese worked from the bunkers underground. Their strategy was for each soldier to kill 10 Americans before he was killed. U.S. Marines rarely saw a Japanese soldier. The losses were staggering. In 36 days of fighting, 6825 U.S. troops were killed and 22,000 were wounded. Virtually all of the 21,000 Japanese defenders were killed. More Marines earned the Medal of Honor on Iwo Jima than in any other battle of U.S. history. Fleet Admiral Chester Nimitz offered the tribute, "Among the men who fought on Iwo Jima, uncommon valor was a common virtue." After its capture, Iwo Jima became an important base for the American military. By war's end, 2400 B-29 bombers carrying 27,000 crewman had made emergency landings on the island.