According to the M. H. Cole "U.S. Military Knives", book III, Camillus was the first to make the USN MK 2 knife during WWII.
They were later also made by PAL, Robeson, Conetta, Utica, and Ka-Bar and marked U.S.N.
Camillus, PAL, Robeson, and Ka-Bar also later made the exact same knife marked U.S.M.C.
For all practical purposes, any Navy MKII is the same knife as a Ka-Bar, and any Ka-Bar is a Navy MKII if it is mil-spec.
The gray plastic U.S.N. MKII scabbard was at first issued with knives to be used by UDT teams.
Later, they became more or less standard issue because of jungle rot quickly eating the leather sheaths in the South Pacific theater.
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