Lieutenant commander (often abbreviated Lt Cdr), formerly more commonly lieutenant-commander, is a senior officer rank in the Royal Navy of the United Kingdom. It is immediately junior to commander and immediately senior to the naval rank of lieutenant.
The equivalent rank in the British Army and Royal Marines is major; and in the Royal Air Force, it is squadron leader.
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Major (Maj) is a military rank which is used by both the British Army and Royal Marines. The rank is superior to captain and subordinate to lieutenant colonel. The insignia for a major is a crown. The equivalent rank in the Royal Navy is lieutenant commander, and squadron leader in the Royal Air Force.
Commander (Cdr) is a senior officer rank of the Royal Navy of the United Kingdom. It is immediately junior to captain and immediately senior to the rank of lieutenant commander. Officers holding the junior rank of lieutenant commander are not considered to be commanders.