Thanks, Tom.
They made them from M-2 steel with a Rc 60-62. Very tough to sharpen but holds a great edge.

I've learned the that the Gerber "Armorhide" handled knife "A" series was designed by Al Mar and produced from 1976-1989. The series was produced in five sizes; 400 (4"), 425 (4.25"), 450 (4.50"), 475 (4.75"), 525 (5.25"). Mostly in Armorhide and some in wood or stag (very collectable). Most models were discontinued about 1985, but the 400 and 525 continued.
I also have a Gerber Miming Carving Set with the sword logo for tool steel.