Some people spend an entire lifetime wondering if they've made a difference.
The Marines don't have that problem. B-29's had been pounding the Japanese islands. However, because of the great distances from U.S. bomber bases in the Marianas, fighter escort was impossible, leaving American bombers vulnerable to Japanese fighter attacks. Roughly 650 miles from Tokyo, the Pacific command set its sights on the 8 square mile island of Iwo Jima as an ideal base for fighter escorts, as well as a refuge for crippled bombers returning from strikes. Anticipating the strong attraction of Iwo Jima and its three airfields to the Americans, the Japanese constructed elaborate defenses of the island that they would defend with suicidal ferocity.