6th Fleet (Imperial Japanese Navy)
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| 6th Fleet (Imperial Japanese Navy) | |
|---|---|
| Name | 6th Fleet |
| Native name | 第六艦隊 |
| Country | Empire of Japan |
| Branch | Imperial Japanese Navy |
| Type | Fleet (Submarine Fleet) |
| Active | 1940–1945 |
| Garrison | Kure Naval District, Yokosuka Naval District |
| Notable commanders | [See Organization and Command Structure] |
6th Fleet (Imperial Japanese Navy) was the submarine-centered fleet of the Imperial Japanese Navy during the Pacific War phase of World War II. Formed from prewar submarine squadrons, it operated in coordination with the Combined Fleet, 1st Fleet, 2nd Fleet, and Southwest Area Fleet across the Philippine Islands, Dutch East Indies, Solomon Islands, and the Aleutian Islands. The 6th Fleet conducted patrols, reconnaissance, fleet engagements, and supply missions, engaging forces such as the United States Navy and the Royal Navy, while interacting with naval institutions like the Kure Naval Arsenal and doctrine from the Naval General Staff (Japan).
History and Formation
The 6th Fleet traced origins to prewar submarine flotillas organized under the Combined Fleet and the Kure Naval District during the Second Sino-Japanese War. With rising tensions after the London Naval Treaty debates and the Tripartite Pact, the Imperial Japanese Navy General Staff reorganized submarine forces into a numbered fleet in 1940 to centralize command for offensive operations in the Pacific Ocean, East China Sea, and Indian Ocean. Early wartime operations were influenced by planners from the Naval Academy (Etajima), doctrines debated by officers associated with the Treaty Faction and the Fleet Faction, and strategic aims coordinated with the Ministry of the Navy (Japan). The fleet’s establishment coincided with campaigns such as the Malayan Campaign, Philippine Campaign, and the Dutch East Indies campaign.
Organization and Command Structure
Command centered on a flagship staff in the Combined Fleet hierarchy with links to the Naval General Staff (Japan), the Yokosuka Naval District, and the Kure Naval District. Commanders included senior submariners who had served on vessels built at the Kure Naval Arsenal and trained at the Yokosuka Naval Arsenal. Subordinate elements comprised submarine squadrons (sensu) grouped into divisions attached to fleets like the 1st Fleet or the 3rd Fleet for specific operations. Liaison occurred with the IJN Naval Air Service for reconnaissance, the Southwest Area Fleet for amphibious logistics, and the Tokyo Express surface units during the Solomon Islands campaign. Administrative matters passed through institutions such as the Ministry of War (Japan)-linked departments and personnel offices influenced by officers with Etajima pedigrees.
Ships and Submarines
The 6th Fleet comprised classes built at arsenals including Kure Naval Arsenal, Mitsubishi Heavy Industries, and Sasebo Naval Arsenal. Prominent submarine classes included the Type B1 submarine, Type B3 submarine, Type C submarine, Type D submarine, and larger cruiser submarines like the I-19 and I-26. Support units featured submarine tenders such as Jingei-class tenders and kaibokan escort vessels built under naval construction programs influenced by the Maru Programme series. Fleet screens included destroyers from classes like the Fubuki-class destroyer and escort craft drawn from the Etorofu-class escort ship. Logistic links ran through bases at Truk Lagoon, Rabaul, Singapore, and Kwajalein Atoll.
Operational Deployments and Battles
6th Fleet submarines participated in early-war offensive patrols during the Attack on Pearl Harbor operational period, later shifting to commerce raiding in the Indian Ocean raid and interdiction against United States Merchant Marine convoys in the Aleutian Islands Campaign and around the Aleutians. Submarines engaged in notable actions during the Battle of Midway reconnaissance phase, the Solomon Islands campaign interdiction efforts, and attacks during the Guadalcanal Campaign supporting Imperial Japanese Army logistics. Vessels such as I-19 achieved dramatic torpedo salvos against Wasp-era task groups and North Carolina-era formations, while other boats laid minefields and executed supply missions to garrisons at Rabaul and Buka Island. As Allied anti-submarine warfare improved with technologies from the United States Navy, Royal Australian Navy, and Royal Navy, including escort carriers like Guadalcanal and destroyer escorts, 6th Fleet losses mounted during convoy actions around Leyte Gulf and the Philippines Campaign.
Tactics, Doctrine, and Technology
Doctrine emphasized long-range reconnaissance, fleet support torpedo attacks, and strategic interdiction shaped by prewar ideas from Etajima-trained staff and influenced by outcomes in the Spanish Civil War and interwar naval conferences. Tactics evolved from coordinated wolfpack-like operations to independent patrols as Allied escort tactics, sonar developments, and airborne radar from units like FAW-10 and VPB-11 degraded submarine effectiveness. Technological aspects included torpedoes such as the Type 95 torpedo and experiments with kaiten manned torpedoes developed late in the war, alongside installations of radio equipment, periscopes produced by firms like Mitsubishi Heavy Industries, and snorkel-like devices adapted from captured concepts. Intelligence interactions involved signals from Hotel Teletype-era naval codes and counterintelligence efforts by MAGIC-era cryptanalysis performed by Allied units.
Postwar Fate and Legacy
After Japan's surrender, remaining 6th Fleet submarines were seized by the United States Navy and scuttled, studied, or scrapped at yards including Sasebo Naval Arsenal and Subic Bay. Former commanders and officers appeared in postwar narratives alongside figures from the Yokosuka Trials and contributed to memoirs linked to the Tokyo Trials era historiography. Legacy influences persisted in postwar Japan Maritime Self-Defense Force submarine doctrine, naval historiography at institutions like the National Institute for Defense Studies (Japan), and cultural representations in works referencing the Pacific War naval dimension. Numerous wartime vessels are subjects of preservation, diving exploration at sites such as Truk Lagoon wrecks, and scholarship in journals tied to Naval War College and universities including Tokyo University and Yokohama National University.