In the Pacific Theater of World War II, the Gilbert and Marshall Islands campaign, from November 1943 through February 1944, were key strategic operations of the United States Pacific Fleet and Marine Corps in the Central Pacific. The purpose was to establish airfields that would allow land based air support for the upcoming operations across the central pacific. The campaign began with a costly three-day battle for the island of Betio at the Tarawa atoll. The campaign was preceded a year earlier by a diversionary raid on Makin Island by U.S. Marines in August, 1942.
The Japanese forces occupied the Gilbert Islands 3 days after the attack on Pearl Harbor, Hawaii. As a provided token defense of Tarawa, they built a seaplane base on Makin and dispersed troops along the coastlines of the atolls to monitor the Allied forces movement in the South Pacific. Following Carlson's Raiders diversionary Makin Island raid of August 1942, the Japanese command was made aware of the vulnerability and strategic significance of the Gilbert Islands. The largest and most strategically important islands of the Gilberts was Tarawa. Fortifications were quickly built up by the Japanese starting in March 1943 with nearly 5,000 troops stationed abroad. An additional 3,000 Special Naval Landing Force and base force troops and 940 naval construction units were supplemented by 1,247 laborers.
By comparison, the Makin islands were held by only a total of 798 combat troops, including some 100 isolated Japanese aviation personnel. General Holland M. Smith, Commanding General of V Amphibious Corps blamed the Carlson raid for the rapid build-up of Japanese forces and staunchly felt, even long after his retirement, that Tarawa should have been bypassed, instead of incurring heavy Marine casualties during the seizure. Admirals Chester W. Nimitz, Ernest King and Raymond A. Spruance did not agree, and believed that retaking the Gilberts to provide an air base for the next step, the battle for the Marshall Islands, was essential for continued movement toward Japan across the Pacific. The code name for the capture of the Gilberts was Operation Galvanic, which called for the seizures of Tarawa, Makin and Apamama.