Frigate Lieutenant is a rank in some navies, especially those of Spain (Spanish: Capitán de Fragata) and Latin America, roughly equivalent to a Sub-Lieutenant in the Royal Navy or a Lieutenant Junior Grade in the US Navy. The French Navy equivalent is a Ship-of-the-Line Ensign (1st Class). A Lieutenant, Junior Grade, is a division officer in the United States Navy. ... The Royal Navy of the United Kingdom is the oldest of the British armed services (and is therefore the Senior Service). ... The United States Navy (USN) is the branch of the United States armed forces responsible for naval operations. ...