"Lieutenant Commander" is a rank senior to Lieutenant and junior to Commander. Lieutenant Commanders are technically Junior Officers, however in practice they occupy a gray area between Junior Officers and Senior Officers.
Lieutenant Commanders serve as Department Heads aboard large starships, and as 1st Officers aboard mid-sized ships. Aboard some small ships, Lieutenant Commanders may be assigned as the Commanding Officer.
Lieutenant Commanders also serve as Department Chairmen at Starfleet Academy.
As described by the Starfleet Field Manual's protocols for uniforms and insignias, the insignia for Lieutenant Commander shall be one Black pip with gold borders and two solid gold pips on the officer's right collar.
STARFLEET RANKS Edit
MARINE RANKS Edit