It's a Camillus made reproduction of the WESTERN L71,(SeaBee) knife of WW2. First time I've seen one that was marked Camillus. Camillus was making these by 1996, however those were marked Western and came with a different sheath than yours.
Back in 1985, Western/Coleman reintroduced the knife for the first time since WW2 production. Those knives have a date code on the blade by the Western name and the leather sheath that came with them was marked USN.
Looking thru the available old catalogs on the Collectors of Camillus website I haven't found an example of one of these. Doesn't look like they had them in 2003 or 2006.
Cool example, thanks for posting.
Also I don't know if any of the original Western L71's were marked USN. The few I've seen weren't.