Lt. Comdr.

Common military ranks in English
Navies	Armies	Air forces
Commissioned and Non-commissioned officers
Admiral of the fleet	Marshal 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	Aircraftman

Lieutenant commander (also hyphenated lieutenant-commander and abbreviated Lt Cdr,LtCdr. or LCDR) is a commissioned officer rank in many navies. The rank is superior to a lieutenant and subordinate to a commander. The corresponding rank in most armies (armed services) and air forces is major, and in the Royal Air Force and other Commonwealth air forces is squadron leader.

The NATO rank code is mostly OF-3.

A lieutenant commander is a senior department officer or the executive officer (second-in-command) on many warships and smaller shore installation, or the commanding officer of a smaller ship/installation. They are also senior department officers in naval aviation squadrons.

Most Commonwealth and other navies address lieutenant commanders by their full rank or the positions they occupy ("Captain" if in command of a vessel). The United States Navy, however, addresses officers by their full rank or the higher grade of the rank. For example, oral communications in formal and informal situations, a Lieutenant (junior grade) is abbreviated as "Lieutenant," and a Lieutenant Commander is abbreviated as "Commander."

Lieutenants were commonly put in command of smaller vessels not warranting a commander or captain. Such a lieutenant was called a "lieutenant commanding" or "lieutenant commandant" in the United States Navy, and a "lieutenant in command," "lieutenant and commander," or "senior lieutenant" in the Royal Navy. The USN settled on "lieutenant commander" in 1862 and made it a distinct rank. The RN followed suit in March 1914.

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Wikipedia