Corvette lieutenant is a rank in some navies, especially those of Spain and Latin America, roughly equivalent to a Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 acting sub-lieutenant or a US Navy ensign

Ensign (rank)

Ensign is a junior rank of a commissioned officer in the armed forces of some countries, normally in the infantry or navy. As the junior officer in an infantry regiment was traditionally the carrier of the ensign flag, the rank itself acquired the name....

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The rank did exist in the French Navy

French Navy

The French Navy, officially the Marine nationale and often called La Royale is the maritime arm of the French military. It includes a full range of fighting vessels, from patrol boats to a nuclear powered aircraft carrier and 10 nuclear-powered submarines, four of which are capable of launching...

 during the Ancien Régime, but has now been replaced with ship of the line ensign (second class) (French: enseigne de vaisseau de deuxième classe).

The NATO rank code is OF-1 (junior)