A good example of a fairly rare buckle of gilt aluminium construction. This is the buckle for the dirk, not the sword, belt, being approximately half the size of the latter. As buckles go, it's the rarer of the two for the sea-going navy.

This near mint sword buckle has no maker's mark. These were worn by navy shore/administrative officials (harbour masters, etc), quite often retired navy personnel who had been wounded, etc. The aluminium with silver finish would have matched the aluminium buttons on the tunic to distinguish this branch of service.