Just acquired an unusual Navy diver.
SS case but with day and date alá the SBS.
Case back has NSN of the SS but has
Royal Marines 0555 instead of Navy 0552.
Crows foot then SP
No issue number or date.

A google trawl reveals a little that SP
was a very limited and specific Naval contract
But the only examples I can find were for
Non dated 0552's.

Watch looks legit, nicely ageing tritium,
Fairly marked crystal but nothing really nasty.
Crown slips when changing hands but can be set with care.

Can any of our mil specialists shed any light on this for me please?

I'm wondering whether it's a bit of a "frankie" ?