On 10 November, 1943, men of the United States Marine Corps invaded the island of Betio, located at the southwest corner of Tarawa Atoll in the Gilbert Islands chain in the Central Pacific. This invasion, known as Operation Galvanic, was a phase of the Pacific Theatre of World War II. The island was declared secure after three days. Given the small size of Betio (0.59 sq. mi.), planners had expected it to take one.