He told me he was on the Indianapolis and it had new oversized propellers put on and that when it turned to the sea they churned up the dead bodies off the sea floor. most of them were drowned never making it to the island.
The drowned and dead marines were on the inside of the lagoon.
The marine casualties were largely in shallow water approaching the invasion beaches. The tide was too low for Higgins boats to cross the reef so the marines had to wade in chest deep water for about half a mile under heavy machine gun and artillery fire. Some units suffered 50-80% casualty rates before they touched the beach.
That is not friendly fire. The marines were forced to wade in because the planners of the Tarawa invasion completely ignored advice about how low the tides would be. There was a congressional inquiry because of the high casualty rate due to poor planning and intelligence. Being the first major amphibious operation of its type, it was all written off as part of the learning curve.