Betio, part of the Tarawa Atoll, is a small, bird-shaped island along the equator in the central Pacific. Early in the morning on November 20, 1943, elements of the Second Marine Division boarded tracked landing vehicles (“amtracs”) and headed for Betio’s beaches. As part of an operation codenamed Galvanic, the Marines hoped to clear the heavily defended island of Japanese forces under the command of Rear Admiral Keiji Shibasaki and capture its vital airfield. The Japanese commander had boasted to …