Iwo Jima was the only Japanese base capable of interfering with American bombing operations against Japan. The entire island was heavily fortified and defended by about 21,700 troops determined to hold it. US Marines faced fanatical resistance once ashore and sustained heavy casualties. Total American losses numbered 17,200 wounded and 6000 dead. Only 200 Japanese troops were captured. Once cleared, the island was used as a fighter base for escorting bombers over Japan and as an emergency landing site for B-29 bombers operating from the Mariannas.