the Iron Curtain, in the German Democratic Republic, WWII Gravity Knives were refurbished and re-issued to the paratroopers and pilots until the existing stock was gone. In the early 1960s two companies then produced an East German Version of the Type I knives. They were then used until the early 1970s. Ibberson gravity knife After British forces had captured numbers of Type I Flieger-Kappmesser, the British government approached George Ibberson & Co. of Sheffield, England, a knife and cutlery manufacturer, and requested production of a British version of the German Luftwaffe Gravity Knife for the Special Operations Executive (SOE) and other clandestine warfare units. Under the initial wartime contract, George Ibberson & Co. made 500 gravity knives for issue to the SOE and other special forces. These Sheffield gravity knives had smooth wood or textured plastic scales, but were otherwise identical in features and operation to the Type I Flieger-Kappmesser, with a locking gravity-deployed blade and a folding rigging spike or awl. In the hands of British SOE agents, the Sheffield gravity knife was considered to be a secondary combat weapon. In addition to the knife blade, SOE close combat instructors found that the folding rigging spike was useful for silent killing of sentries by opening the carotid artery on the neck. 'False gravity' and non-gravity knives Some folding or telescoping knives that can open their blades by force of inertia or gravity were not intended or advertised by the manufacturer to do so. Knives that will lock their blades open, but do not have any closed position lock device are referred to as "false" gravity blades. The illustration shows the internal parts of a 1960s Japanese import 'false' gravity knife. Other knives may be considered to be 'false' gravity knives, including certain lock-back and liner lock folding knives that will not lock a blade in both open and closed positions. After the passage of the Switchblade Knife Act in the U.S. in 1958, it was discovered that some U.S. businesses were importing folding stiletto knives without spring mechanisms that did not have a pronounced blade heel (internal surface) in the pivot area allowing the longer 11 and 13 inch-bladed models to easily flick open. Modern (post 1965) folding stilettos imported or distributed in the U.S. now have blade heels that are intentionally pointed and ratchet against the lockback mechanism, preventing inertia opening. Other knives commonly mistaken for gravity knives