We never had anybody from the Army or Marines other than taking SBS people and their boats to do whatever they did . I believe they would never lounge about like this fellow --- they were hard smart men, who never smiled and I suspect though our crew were an oily rabble.
Its obviously some sort of formal occasion and no skipper I ever had would have anybody on the bridge unless needed and properly dressed, but its WWII

I don't recall a Marine at Dolphin, but maybe there were some on the big depot ships, doing normal big ship duties, but nothing connected with the boats.
We had some sabotage problems in Pompey dockyard in about 1953, but we provided more direct security for the boat ourselves while the general security was provided by the Dockyard police. The TOTEM appears to be in the Dockyard in the pic'.
As far I am concerned this fellow is certainly an odd one out !
Lofty