Section 125(3)(d) in The Naval Ceremonial, Conditions Of Service And Miscellaneous Regulations, 1964
(d)Lieutenants. - Sub-Lieutenants shall be appointed to sea for sea training and award of Certificate of Competency. 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 Certificate of Competency;(ii)they are recommended by their Commanding Officers as fit in all respects for promotion to the rank of Lieutenant.