It has a NATO ranking code of OF-2, equivalent to a Lieutenant in the Royal Navy or a Captain in the British Army.
On 1 April 1918, the newly created RAF adopted its officer rank titles from the British Army, with Royal Naval Air Service Lieutenants and Royal Flying Corps Captains becoming Captains in the RAF. In response to the proposal that the RAF should use its own rank titles, it was suggested that the RAF might use the Royal Navy's officer ranks, with the word "Air" inserted before the naval rank title. For example, the rank that later became Flight Lieutenent would have been Air Lieutenant. However, the Admiralty objected to this modification of their rank titles. The rank title Flight Lieutenent was chosen as Flights were typically led by RAF Captains. The rank of Flight Lieutenent has been used continuously since 1 August 1919.
Air Training CorpsEdit
Although the highest substantive rank in the Volunteer Reserves is Flying Officer it is common practice for officers to be promoted to Acting Flight Lieutenent in order to allow them to command an ATC squadron.
An officer in the Volunteer Reserves can be promoted to acting (unpaid) Flight Lieutenent after nine years of continuous service regardless of whether or not he or she is in command of a squadron.