American preparations

Starting on 15 June 1944, the U.S. Navy and the U.S. Army Air Forces began naval bombardments and air raids against Iwo Jima, which would become the longest and most intense in the Pacific theater.[17] These would contain a combination of naval artilleryshellings and aerial bombings that went on for nine months. On 17 June, the destroyer escort USS Blessman sent Underwater Demolition Team 15 (UDT-15) toward Blue Beach for reconnaissance. The Japanese infantry fired on them, killing one American diver. On the evening of 18 June, the Blessman was hit by a bomb from a Japanese warplane, killing 40 sailors, including 15 members of her UDT.

Unaware of Kuribayashi’s tunnel defense system, many of the Americans assumed the majority of the Japanese garrison were killed by the constant bombing raids.