Lieutenant commander
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.
Etymology
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, in day-to-day speech, a Lieutenant (junior grade) is abbreviated as "Lieutenant," and a Lieutenant Commander is abbreviated as "Commander."