Section 123(3)(d) in The Naval Ceremonial, Conditions Of Service And Miscellaneous Regulations, 1964
(d)Lieutenants. - Sub-Lieutenants shall be appointed to sea for Watchkeeping duties. They shall be promoted to the rank of Lieutenant at the discretion of the Chief of the Naval Staff provided:(i)they have obtained the Engine Room Watchkeeping Certificates;(ii)they are recommended by their Commanding Officers as fit in all respects for promotion to the rank of Lieutenant.]