Truk is a collection of hilly islands in the Central Pacific. It is an atoll surrounded by a barrier reef. During the Pacific War, Truk was a part of the Japanese Empire where they established a notable naval base.
Before the Pacific War, the Imperial Japanese Navy established a naval base at Truk comparable to Pearl Harbor. As such, it provided the navy's warships with some of the best fleet anchorages in the region. It was there that they stationed many of their capital ships, such as the Yamato-class battleships, alongside more lightweight naval units. In addition, Truk also included notable submarine bases. With a large part of the IJN's fleet stationed there, Truk was the base for Japanese operations in New Guinea and the Solomon Islands.
Nor was Truk just a naval base. There were also various airfields located around Truk. At Moen they built one bomber strip, combined seaplane base and fighter strip for their aircraft. In Dublon the Japanese added an aviation repair and supply station. Consequently, they stationed hundreds of planes there. It was the one major Japanese air base that was within range of the Marshall Islands, and its planes provided notable support for their garrisons scattered around the Central and South Pacific.
As an air and naval base, it was a considerable fuel storage site. Japan had storage for about 77,200 tons of oil at Truk. That included underground and above-ground steel tanks. Consequently, it was one of their largest fuel depots beyond the Japanese home islands and a stopping point for IJN warships to refuel.
Given the assortment of warships and aircraft at Truk, the IJN fortified it with various fortifications. Japan garrisoned thousands of troops there. They added coastal guns around its coastline, and various anti-aircraft guns. Additional sub and torpedo nets were placed in the surrounding waters. Minefields were also laid in the lagoon. However, Truk still lacked piers and shore services for its ships.
The Allies were advancing in the Pacific by 1944. In 1943, U.S. Marines had already occupied Guadalcanal and Tarawa. The island hopping strategy, with which they occupied Japanese islands in the Pacific, targeted the occupation of the Marshall Islands. There, they could construct further forward bases for the island hopping campaign toward the Japanese home islands.
In early 1944, the U.S. Marines invaded the Marshall Islands. They occupied both the Kwajalein and Majuro atolls by February. However, with further landings at Eniwetok still required the campaign was not over.
The Allies also had Task Force 58 to provide further naval support for the campaign. This was a formidable fleet of warships that included five aircraft carriers, several battleships and other surface fleet ships. With Task Force 58 aircraft the Allies could bomb Japanese land targets in the Pacific.
The proximity of Truk with the Marshalls provided a potential resupply route for the Japanese. Truk could potentially provide more reinforcements and supplies for the Japanese garrison in the Marshalls. In addition to this, its aircraft could also provide further air support for the campaign. As such, Task Force 58 sailed for Truk. The Allies sent Task Force 58 to wipe out Truk's ships and aircraft, which would ensure Allied naval and air superiority for the Marshall Islands Campaign.
However, the IJN expected Truk might emerge as a target for U.S. airstrikes in 1944. U.S.reconnaissance planes gave the Japanese further forewarning that a carrier fleet was approaching the base. To prevent a devastating airstrike, the IJN withdrew most of the capital ships at Truk before Task Force 58 arrived. What was left were more lightweight surface fleet ships such as cruisers and destroyers.
Consequently, when TF 58 moved to within range fewer IJN ships were at the naval base. But hundreds of Japanese aircraft were still stationed at the airfields. A few of those were airborne when the first U.S. planes approached the harbor. They provided some air cover for the naval base and intercepted the first U.S. planes, but overall TF 58 had relatively light losses during the airstrike.
Task Force 58 ravaged most of the IJN cruisers and destroyers at Truk. The raid also wiped out hundreds of Japanese aircraft. This left Truk cutoff from further supplies, and ensured Allied naval and air superiority for the Marshall Island Campaign. The rest of the Marshall Islands also fell to the Marines as the Allies island hopped their way toward the Mariana Islands.