From what I saw, there are marines references in every novel but Atropos. (Which has a negative reference: Forester claimed Atropos was too small to have a marine contingent. But Hotspur was even smaller and he did give her a marine contingent, so...? I assume this is like the thing where no ship of his written before 1950 has a wardroom, regardless of size, but every ship after 1950 has a wardroom, regardless of size.) A lot of the references are piping-aboards or sentry-duty, but the references become much more extensive in shore-based actions. There's also quite a long passage when Sawyer falls in Lieutenant (wherein a corporal exposits events that Bush didn't witness), and of course the whole story of the mutinous marine-bandsman in West Indies.

And yay, a photo of the shoulder knot! I was trying to envision what that might look like (and had vague memories of paintings that maybe showed it?), so I'm glad of the reference.