Love the properly loaded bit ! Strictly that is a dray and they are draymen, but what a great photo. Until quite recently a brewery (Courage I think) still delivered to central London like that. The dray also used to appear in the Lord Mayor's show.
Yep, there's Navy in there, as well as Marines. It's the Ships Company from the USS Constellation in Baltimore (has both sailors and Marines). I belong to this unit as a Marine Musician--I marched with them once before, but this year I went with an Army fife and drum corps. Here's another picture of them--looking sharp!