After bombardment by the battleships USS Maryland and USS Mississippi and further bombardment by aircraft, the first wave of US marines attempted to land on Betio Island, the most heavily defended section of the atoll. The reef proved a formidable obstacle. A second wave of marines followed soon after and there was bloody fighting when they reached the beach.
The Japanese defenders had a wide range of heavy weapons, including tanks, and were well-positioned in hidden pillboxes and bunkers. American casualties were high. The Marines were to suffer over 3,000 casualties by the time their hold on Betio Island was secure. Japanese (and Korean) losses were even greater.