Section 121(3)(d) in The Naval Ceremonial, Conditions Of Service And Miscellaneous Regulations, 1964
(d)Lieutenants. - Confirmed Sub-Lieutenants shall be appointed to sea and shall be promoted to the rank of Lieutenant at the discretion of the Chief of the Naval Staff, provide they have obtained the following certificates from their Captains:(i)that the officer is competent to take charge of a Watch at sea as Lieutenant and to perform efficiently the duties of that rank;(ii)that he is recommended and is fit in all respects for promotion to the rank of Lieutenant.