Marble's Arms Corporation designed the first
Jet Pilot Survial Knife in 1957 based on the Marble's Ideal hunting knife. But Marble's ultimately didn't get the military contract for full production.
Camillus did and produced the knives based on the blueprints and specifications that Marble's had sold to the government.
1958 was the first year of production and the knives featured a 6-inch blade and a screw-on pommel. Sometime within that first year, Camillus received permission from the military to switch to a peened pommel to cut costs. They kept the 6-inch blade. This second version was produced from about 1958-1961. Around 1962, the military contract was amended to shorten the blade to 5 inches. Camillus produced the 5-inch version for the military until 1985 when they lost the contract to Ontario.
Camillus Jet Pilot Survival Knife, 1st Version, 6-inch blade, c.1958 with screw-on pommel
Camillus Jet Pilot Survival Knife, 2nd Version, 6-inch blade, c.1958-1961 with peened pommel
Camillus Jet Pilot Survival Knife, 5-inch blade version, c.1985 (the final year of the Camillus military contract)
EDITED: to add "Jet" in front of Pilot Survival Knife to distinguish from earlier PSKs which are a different style knife.