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In Japanese, sentai (戦隊) is a military unit and may be literally translated as "squadron", "task force", "group" or "wing". The terms "regiment" and "flotilla", while sometimes used as translations of Sentai, are also used to refer to larger formations.
World War II 
It is perhaps best known as a term used during World War II by the military of the Empire of Japan, for Imperial Japanese Army Air Force (IJAAF) and Imperial Japanese Navy Air Service (IJNAS) military aviation units equivalent to a group or wing in other air forces. However, the term had slightly different meanings in the IJAAF and the IJNAS.
An IJAAF Sentai was made up of two to four squadrons (chūtai). In the IJAAF, two or more Sentai comprised a hikōdan (air brigade). In the later stages of World War II, the IJAAF abolished chūtai and divided its sentai into hikōtai (flying units) and seibitai (maintenance units). A sentai commander (sentaichō) was generally a Lieutenant Colonel.
In the IJNAS, a sentai was a larger unit: a kōkūtai was the equivalent of an IJAAF sentai. Several sentai made up a kantai (air fleet). In the IJNAS, a Sentaichō was usually a Naval Captain.
Sentai in the Japanese Navy was prescribed by a law the Naval military command No. 10, Kantairei (艦隊令) on 30 November 1914. It is as follows if paraphrase them.
- Sentai (戦隊, Battleship Division, Battlecruiser Division, Cruiser Division, Minelayer Division or Coast defence ship Division): organized by and over two warships as surface combatant.
- Kōkū Sentai (航空戦隊, Carrier Division or Air Flotilla): organized by and over two aircraft carriers, seaplane tenders or air groups.
- Suirai Sentai (水雷戦隊, Torpedo Squadron or Cruiser-Destroyer Squadron): organized by a few warships (cruiser as destroyer squadron leader) and some destroyer divisions.
- Sensui Sentai (潜水戦隊, Submarine Squadron): organized by a few warships (submarine tender or cruiser as submarine squadron leader) and some submarine divisions. The 1st Sensui Sentai (ex-4th Suirai Sentai) was independent from Suirai Sentai on 1 April 1919.
- Yusō Sentai (輸送戦隊, Landing ship Squadron): organized by some landing ship divisions. First unit the 1st Yusō Sentai was organized on 25 September 1944.
- Tokkō Sentai (特攻戦隊, Suicide Attack Division): organized by mother ship and suicide weapon Kaiten, Kairyū, Kōryū and Shin'yō. First unit the 1st Tokkō Sentai was organized on 20 March 1945.
Cultural references 
The Super Sentai Series (スーパー戦隊シリーズ Sūpā Sentai Shirīzu ) is a franchise of Japanese tokusatsu television dramas that uses the word sentai to describe a group of three or more costumed superheroes who often pilot fictional robotic vehicles.
See also 
- Dan Ford, 2004-05, "An introduction to the Japanese Army Air Force" (warbirdforum.com)
- Mark Kaiser, 1997-98, "Unit structure of IJA Air Force" (self-published)
- Mitch Schwartz, 2001, "East Asian/Pacific Area" (self-published)
- Peter Dunn, 2002, "Japanese Navy Air Force (JNAF) Operating in the Australian Area During WW2" (ozatwar.com)
- Series 100 year histories from Meiji Era, Ministry of the Navy, printed by Hara Shobō (Japan)
- Vol. 173, Histories of Naval organizations #3 (1), original plot in 1939, reprint in May 1971
- Vol. 174, Histories of Naval organizations #3 (2), original plot in 1939, reprint in July 1971