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Frigate lieutenant is a rank in some navies, especially those of Spain (Spanish: Alférez de Navío) and Latin America, roughly equivalent to a sub-lieutenant in the Royal Navy or a lieutenant (junior grade) in the US Navy.

The rank of Frigate Lieutenant (officially Light Frigate Lieutenant, lieutenant de frégate légère) was a rank in the French Royal Navy until 1786. It was used by officers promoted from outside the ranks of the gardes de la marine, such as merchant navy officers, promoted volunteers or colonial gentry. The rank of Frigate Lieutenant was equivalent, but junior to, to the rank of Ship Ensign. Some Frigate Lieutenants were eventually promoted Fireship Captains (capitaines de brulôt), equivalent to Ship-of-the-Line Lieutenants.

The NATO rank code is OF-1 (senior)