The knife was originally made by Imperial for the us Navy UDT teams. Designed in late fifties and made until the 1980's in several batches. Only about 1300 or so were made by two or three companies. They are non-magnetic made of haynes alloy no.25 which it consists of a copper-chromium-tungsten-nickel alloy. The reasons for choosing this alloy aside from the non-magnetic, non-rusting and non-sparking properties is its ability to be hardened to allow it to hold a cutting edge. Haynes Alloy No. 25 is mainly used in the aerospace industry for turbine engine parts. Later models were made of Nitinol, a Nickel Titanium alloy developed by the Naval Ordnance Laboratory in MD. The saw back is capable of cutting wire rope. It had to have a low magnetic signature so not to set off mines and therefore could not have any steel or iron content.
Regards, Vince