A gravity knife is a knife with a blade contained in its handle, and that opens its blade through the force of gravity. This mechanism of opening is fundamentally different from the switchblade, which extends its spring-propelled blade automatically upon the push of a button, switch, or fulcrum lever. The main purpose of gravity opening is that it allows opening and closing to be done one handed, in situations where the other hand is occupied. Hence, historically they have been issued to parachutists to cut off caught lines, such as lines tangled in trees, a major potential use of the gravity knife. The gravity knife uses a button, trigger, or fulcrum lever to release the blade from both the open and the closed positions, and may use a side-folding or telescoping (out-the-front, or OTF) blade. While most military gravity knives utilize a locking blade design, other types may not mechanically lock open but rely instead upon friction to wedge the rear section of the blade against the interior of the handle. Factory-made gravity knives have various types of buttons, triggers, and fulcrum levers, which usually are used to release the blade from both the open and the closed positions. Design and operation Flieger-Kappmesser / Luftwaffe Gravity Knife (LGK) One of the most recognizable gravity knives is the World War II-era Flieger-Kappmesser (literally: "flyers-cutting knife"), which utilizes a four-inch (100 mm) telescoping (OTF), gravity-propelled locking blade. First produced in 1937, the often so called Fallschirmjägermesser was initially issued to German flight crews and paratroops, primarily for the purpose of cutting a trapped parachutist from his rigging in case he landed with a tangled parachute, or became entangled in trees or in the water with the shroud lines. The spike was used to untie knots while packing the parachutes. Luftwaffe air crew members used the knife to cut themselves out of their harnesses or cut through the aluminum hull of the aircraft after a crash landing. Though not intended for use as a fighting knife in the first place, the LGK was introduced to the 1st Skijäger Division and SS units on the Eastern Front to be used primarily as a close combat weapon from 1944 on. The Flieger-Kappmesser uses a sliding blade inside a metal gripframe, which was originally fitted with smooth wood scales. The blade itself is a relatively blunt spear-point, and the profile is flat ground, tapering to a