I think it is a bit more complicated than that......the knives may be the same but the nomenclature depends upon whom they were made for.
I believe that ,if they were made for the Navy (US), they were Mk2s.....the Marines called the same knife the Mk 3.
"Ka-Bar " was a completely unofficial and erroneous name. Union (?) Cutlery ( Ka-bar} was just one of several makers.....the name just stuck.
The US Navy issue knife is, now, the Mk 3
and, I think, is made by Ontario. Blade shape is similar to the Kalashnikov rifle bayonet.
But, I am sure, someone more informed than I will fill in the gaps.
Anyway, a genuine Mk 2 Navy is ,most likely, of WW2 vintage........??
I look forward to a more erudite view.
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Brian W E
ICQ #21525343
Money : spend it before it's all gone