In the days after the landings, the Marines expected the usual Japanese banzai charge during the night. This had been the standard Japanese final defense strategy in previous battles against enemy ground forces in the Pacific, such as during the Battle of Saipan. In those attacks, for which the Marines were prepared, the majority of the Japanese attackers had been killed and the Japanese strength greatly reduced. However, General Kuribayashi had strictly forbidden these “human wave” attacks by the Japanese infantrymen because he considered them to be futile.
The fighting on the beachhead at Iwo Jima was very fierce. The advance of the Marines was stalled by numerous defensive positions augmented by artillery pieces. There, the Marines were ambushed by Japanese troops who occasionally sprang out of tunnels. At night, the Japanese left their defenses under cover of darkness to attack American foxholes, but U.S. Navy ships fired star shells to deny them the cover of darkness. On Iwo Jima (and other Japanese held islands), Japanese soldiers who knew English were used to harass and or deceive Marines in order to kill them if they could; they would yell “corpsman” pretending to be a wounded Marine, in order to lure in U.S. Navy medical corpsmen attached to Marine infantry companies.
The Marines learned that firearms were relatively ineffective against the Japanese defenders and effectively used flamethrowers and grenades to flush out Japanese troops in the tunnels. One of the technological innovations of the battle, the eight Sherman M4A3R3 medium tanks equipped with a flamethrower (“Ronson” or “Zippo” tanks), proved very effective at clearing Japanese positions. The Shermans were difficult to disable, such that defenders were often compelled to assault them in the open, where they would fall victim to the superior numbers of Marines.
Close air support was initially provided by fighters from escort carriers off the coast. This shifted over to the 15th Fighter Group, flying P-51 Mustangs, after they arrived on the island on 6 March. Similarly, illumination rounds (flares) which were used to light up the battlefield at night were initially provided by ships, shifting over later to landing force artillery. Navajo code talkers were part of the American ground communications, along with walkie-talkies and SCR-610 backpack radio sets.
After running out of water, food and most supplies, the Japanese troops became desperate toward the end of the battle. Kuribayashi, who had argued against banzai attacks at the start of the battle, realized that defeat was imminent.
Marines began to face increasing numbers of nighttime attacks; these were only repelled by a combination of machine-gun defensive positions and artillery support. At times, the Marines engaged in hand-to-hand fighting to repel the Japanese attacks. With the landing area secure, more troops and heavy equipment came ashore, and the invasion proceeded north to capture the airfields and the remainder of the island. Most Japanese soldiers fought to the death.