In the military the rank structure sometimes has little to do with the command structure on the flight deck, this can lead to amusing situations at times such as once when I was a two striper in the Airforce rank structure but also the aircraft Captain, my F/O was a squadron leader with two and a half stripes and my 'second officer' was a wing commander, three stripes.
We pulled ap at Singapore/Changhi in a B707 and after shutdown the local handling agent came to the flight deck with some 'official' paperwork to be signed and looked around at all the stripes and picked the wing commander, who had the most, and handed him the paperwork. He said he wasn't the Captain so the squadron leader was handed the papers, he also said he wasn't the Captain so I as the Captain, with the least number of stripes, eventually got to autograph the paperwork.
Regards,
BH.