Fourth Fleet (Imperial Japanese Navy)

Fourth Fleet (Imperial Japanese Navy) was a fleet of the Imperial Japanese Navy primarily tasked with defending the South Seas Mandate and conducting operations in the South Pacific. Initially formed in 1905, it was re-established in 1937 and played a significant role in the early Pacific War, including the invasion of Wake Island and the Battle of the Coral Sea. The fleet was largely relegated to garrison and transport duties after heavy losses in 1942 and was formally dissolved at the end of World War II.

History

The Fourth Fleet was first created in 1905 during the Russo-Japanese War but was soon disbanded. It was permanently re-established on 15 November 1937, as part of the Imperial Japanese Navy's expansion during the Second Sino-Japanese War, with its headquarters at Truk Lagoon in the Caroline Islands. Its primary mission was the defense of Japan's South Seas Mandate, a vast area of Micronesia granted after World War I. Under the command of the Combined Fleet, the fleet's responsibilities grew with the escalation of tensions with the United States and the United Kingdom, leading to its involvement in the opening campaigns of the Pacific War.

Organization

The organizational structure of the Fourth Fleet was fluid, typically centered around a core of light cruisers, destroyers, submarines, and auxiliary ships, supported by naval base forces and airfield units. It was administratively part of the Combined Fleet and often worked in conjunction with other units like the Fifth Fleet and the Eighth Fleet. Key subordinate commands included the 6th Submarine Squadron, the 19th Minesweeper Division, and various Special Naval Landing Forces. The fleet also controlled important naval air bases at Rabaul, Kavieng, and Kwajalein, which housed Mitsubishi A6M Zero fighters and Mitsubishi G4M bombers.

Commanders

Commanders-in-Chief of the Fourth Fleet were senior Imperial Japanese Navy officers, often vice admirals or admirals. Notable commanders included **Shigeyoshi Inoue**, who led during the Battle of the Coral Sea and was a proponent of naval aviation. He was succeeded by **Mineichi Koga**, who later became commander of the Combined Fleet. Other commanders were **Eikichi Katagiri** and **Masami Kobayashi**, who oversaw the fleet's later defensive and logistical operations. The chief of staff was a key position, with officers like **Yoshio Suzuki** and **Shikazo Yano** serving in this role, coordinating operations with the Imperial General Headquarters.

Operational history

The Fourth Fleet's operational history began with patrols and shows of force in the South Seas Mandate prior to the war. Upon the outbreak of the Pacific War, it spearheaded the invasion of Wake Island in December 1941, though the initial assault was repulsed by United States Marine Corps defenders. In early 1942, it supported the invasion of Rabaul and operations in the Solomon Islands. Its most significant engagement was the Battle of the Coral Sea in May 1942, where it aimed to capture Port Moresby but was turned back by United States Navy and Royal Australian Navy forces, losing the light aircraft carrier Shōhō. After this defeat and heavy losses during the Guadalcanal campaign, the fleet's role diminished to garrison duty, convoy escort, and reinforcement runs, suffering continual attrition from United States Navy submarines and aircraft based at Tarawa and Eniwetok.

Ships assigned

Throughout its existence, the Fourth Fleet was assigned a variety of warships, though rarely the Imperial Japanese Navy's newest or most powerful capital ships. Notable vessels included the light cruisers Katori (often used as a flagship), Kashima, and Yūbari. Destroyer divisions featured ships of the Mutsuki and Fubuki classes, such as Yūgure and Mutsuki. The fleet also operated submarine tenders like Jingei, minelayers including Okinoshima, and numerous auxiliary ships, gunboats, and patrol boats. The light aircraft carrier Shōhō was briefly attached during the Battle of the Coral Sea before its sinking.

Category:Fleets of the Imperial Japanese Navy Category:Military units and formations established in 1937 Category:Military units and formations disestablished in 1945