Section 251(1) in The Naval Ceremonial, Conditions Of Service And Miscellaneous Regulations, 1964
(1)The relative seniority of officers of the Indian Navy, Army and Indian Air Force, holding equivalent ranks, who serve together in an Inter-Service Organisation shall be determined as follows:(a)Officers holding equivalent substantive rank (and no acting rank) shall rank according to their seniority in the substantive rank, and(b)Officers holding acting rank shall rank after officers holding corresponding substantive rank. Officers of equivalent acting ranks in relation to each other shall rank according to their seniority in the substantive rank.
