The Battle of Tarawa occurred as a result of the American invasion of the Tarawa Atoll, located in the Gilbert Islands about halfway between Papua New Guinea and Hawaii, being the first offensive of the U.S. military in the central Pacific during World War 2.
Map source: Oceania_ISO_3166-1.svg: User:Tintazul. Derivative work: Cruickshanks [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
The Americans needed air bases to capture the Micronesian islands that stood between them and Japan, e.g the Marshall Islands being taken into account for a possible invasion. However, Betio - the largest island in the Tarawa Atoll - was hosting a Japanese garrison and air base, which could threaten the U.S. Navy's line of communications between Hawaii and the Marshall Islands.
Betio - an island just 2 miles (3.2 km) long, with a lagoon in the northern side and open ocean on the southern side - had been heavily fortified by the Japanese with five hundred pillboxes, forty artillery pieces in reinforced firing pits, and fourteen coastal defense guns.
Two units of Special Naval Landing Forces - the marine troops of the Imperial Japanese Navy - were deployed on the island, including fourteen Type 95 light tanks. The U.S. invasion force consisted of the 2nd Marine Division and elements of 27th Infantry Division, backed by the U.S. Fifth Fleet.
In the predawn hours of November 20, 1943, an artillery duel erupted
between the Japanese coastal guns and the U.S. battleships, resulting in
silencing the Japanese artillery. The U.S. Navy's warships bombarded
the island for three hours from 06:10 a.m., after which two minesweepers
cleared the lagoon of mines.
An unexpected problem was the tide, which did not rise enough in the lagoon, the water depth being only three feet over the reef. The Higgins boats (LCVP) of the U.S. Marines could not pass, only the LVT "Alligators", which were tracked, went over the reef. As the LVTs were approaching the beach, many were hit by the Japanese fire. Colonel David Shoup, the commander of the 2nd Marine Regiment, took command of all landing troops and, although wounded, provided an inspired leadership of the Marines throughout the critical two days after the landing. A few Sherman tanks managed to reach the shore, helping the Americans to advance beyond the sea wall.
In mid-afternoon of the first day, an American naval artillery shell killed the commander of the Japanese garrison and most of his staff.
the second day, benefiting from naval and air support, the Americans
took control of the western side of the island, where new troops and
heavy equipment were to be landed.
In the last two days of battle, the Marines advanced towards the eastern side of the island, annihilating one by one the Japanese pockets of resistance. The most serious Japanese counterattack was a typical banzai charge launched at night, but it was repelled with the help of two U.S. destroyers.
The losses suffered in the battle were quite high for a tiny island, some coming from the sinking of the escort carrier USS Liscome Bay by a Japanese submarine.
By winning the battle of Tarawa, the U.S. military was in a position to continue the offensive in the central Pacific, the next target being the Marshall Islands. The lessons learned after the Tarawa Atoll's invasion - one of them leading to creation of Underwater Demolition Teams (UDT) - were applied in subsequent amphibious landings.