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.
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 Service (IJAAS) 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 IJAAS and the IJNAS.
An IJAAS Sentai was made up of two to four squadrons (chūtai). In the IJAAS, two or more Sentai comprised a hikōdan (air brigade). In the later stages of World War II, the IJAAS 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 IJAAS sentai. Several sentai made up a kantai (air fleet). In the IJNAS, a Sentaichō was usually a Naval Captain.