Lieutenant Commander

Lieutenant Commander
Lieutenant Commander T'Pang in 2415
Lieutenant Commander Rank Insignia

The Starfleet line rank immediately inferior to Commander, and superior to Lieutenant. Officers with this rank typically hold positions as senior department heads on larger vessels such as the Galaxy and Sovereign class, and may also serve as the executive officer of smaller or older vessels. On larger starships, the second officer usually holds this rank (such as Data of the U.S.S. Enterprise or Tuvok of the U.S.S. Voyager).

Officers of this rank typically have anywhere between 5-15 years of experience in Starfleet.

Decorum

When introducing a Lieutenant Commander, it is proper to introduce them using their full rank. However, it is polite to address them (and refer to them) as "Commander." For an inferior officer to address a Lieutenant Commander as "Lieutenant" is considered a severe breach of decorum. It is risky for inferior officers to address them as "Lieutenant Commander", as well. Some may take offense; others may not care.