Flt Lt

Common military ranks in English
Navies	Armies	Air forces
Commissioned and Non-commissioned officers
Admiral of the fleet	General of the Army or Field marshal	Marshal of the air force
Admiral	General	Air chief marshal
Vice admiral	Lieutenant general	Air marshal
Rear admiral	Major general	Air vice-marshal
Commodore	Brigadier or Brigadier general	Air commodore
Captain	Colonel	Group captain
Commander	Lieutenant colonel	Wing commander
Lieutenant commander	Major or Commandant	Squadron leader
Lieutenant	Captain	Flight lieutenant
Sub-lieutenant	Lieutenant or First lieutenant	Flying officer
Ensign	Second lieutenant	Pilot officer
Midshipman	Officer cadet	Flight cadet
Enlisted grades
Warrant officer or Chief petty officer	Warrant officer or Sergeant major	Warrant officer
Petty officer	Sergeant	Sergeant
Leading seaman	Corporal	Corporal
Seaman	Private or Trooper	Aircraftman
·

Flight Lieutenant (Flt Lt in the RAF and IAF; FLTLT in the RAAF and RNZAF—formerly sometimes F/L in all services) is a junior commissioned air force rank that originated in the Royal Naval Air Service and is still used in the Royal Air Force and many other countries, especially in the Commonwealth. It is also sometimes used as the English translation of an equivalent rank in non-English-speaking countries, especially those with an air force-specific rank structure.

Flight lieutenant ranks above flying officer and below squadron leader. The name of the rank is the complete phrase; it is never shortened to "lieutenant".

It has a NATO ranking code of OF-2, and is equivalent to a lieutenant in the Royal Navy and a captain in the British Army and the Royal Marines. The equivalent rank in the Women's Auxiliary Air Force (WAAF), Women's Royal Air Force (WRAF) (until 1968) and Princess Mary's Royal Air Force Nursing Service (PMRAFNS) (until 1980) was flight officer.

On 1 April 1918, the newly created RAF adopted its officer rank titles from the British Army, with Royal Naval Air Service lieutenants (entitled flight lieutenants and flight commanders) 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 current rank of flight lieutenant would have been "air lieutenant". Although the Admiralty objected to this simple modification of their rank titles, it was agreed that the RAF might base many of its officer rank titles on navy officer ranks with differing pre-modifying terms. It was also suggested that RAF captains might be entitled flight-leaders. However, the rank title flight lieutenant was chosen as flights were typically commanded by RAF captains and the term flight lieutenant had been used in the Royal Naval Air Service. The rank of flight lieutenant has been used continuously since 1 August 1919.

...
Wikipedia