Corvette lieutenant is a rank in some navies, especially those of Spain and Latin America, roughly equivalent to a Royal Navy acting sub-lieutenant or a US Navy ensign.
The rank did exist in the French Navy 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)
References
Corvette lieutenant Wikipedia(Text) CC BY-SA