UK
Captain-lieutenant was formerly a rank in the British Army; the senior subaltern rank, above lieutenant and below captain.
A regiment's field officers - its colonel, lieutenant colonel, and major - originally commanded their own companies, as well as carrying out their regimental command duties.
However, from the 17th century onwards, the colonel increasingly became a patron and ceremonial head instead of an actual tactical commander, with command in the field devolving to the lieutenant colonel. This left the colonel's company without a captain.
The lieutenant of this company thus became its acting captain. This state of affairs was formally recognised with the creation of the rank of captain-lieutenant, with its own entry in the table of prices for the purchase of commissions.
The rank was abolished sometime in the early 19th century.
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