RAF Mk16a Flying Suit Aircrew parachute cutter.

It is known as the 'Aircrew Cutter' and the blade is made of an extra-special steel, capable of cutting through Kevlar strapping which contains particles of carbon and other components that are very difficult to sever.

It is stamped on the casing... F.E.& J.R Hopkinson 22C/5670707

The operation is simply to hook the 'beak' over the strap to be cut and pull - the razor shrp steel does the rest.

The operation of the sliding button (as seen in pic) is for scoring and puncturing an inflated life jacket that might be causing release problems.