United States Marines launched a bold assault on Tarawa Atoll, a tiny island in the Gilbert Islands, as part of Operation Galvanic. The Marines, arriving in amphibious assault vehicles, were met with a maelstrom of fire from Japanese shore guns and machine guns. The atoll, only a mile wide, was heavily fortified, with the Japanese defenders determined to hold their ground. The Marines fought bravely, but the intense resistance led to heavy casualties on both sides.