cut through the fuselage of downed aircraft to rescue trapped personnel and a hollow handle to allow storage of survival gear. Randall made the changes and the result was the first of the modern survival knives. During the Vietnam War, the Gerber Mark II, designed by US Army Captain Bud Holzman and Al Mar, was a popular fighting knife pattern that was privately purchased by many U.S. soldiers and marines serving in that conflict. In the 1970s and 1980s a student and protege of Fairbairn, Colonel Rex Applegate worked with knife designer Bill Harsey, Jr. to design the Applegate-Fairbairn Combat Knife, so named because it was designed as an improvement on the Fairbairn–Sykes based upon discussions Applegate and Fairbairn had during World War II to eliminate the weaknesses of the F-S knife (e.g., weak blade point, inability to determine orientation of blade merely by grip). While the Applegate-Fairbairn combat knife had a blade design that was more versatile than the F-S fighting knife, the former remained primarily a single-purpose fighting knife design. The first of these knives were made by Al Mar Knives, based on Harsey's designs. Tactical knife A tactical knife is a knife with one or more military (martial) features designed for use in extreme situations. In popular usage the terms "fighting knife" and "tactical knife" are frequently employed interchangeably, although tactical knife is principally designed to be used as a utility tool, not as a weapon. Folding knives are rarely if ever designed primarily for use as fighting knives or combat knives. However, many armies and military organizations have issued folding "utility" knives that were not intended to be used as weapons, but which had tactical features that appealed to military personnel as well as civilians. This includes the German Mercator "Black Cat" folding utility knife, the German Luftwaffe Fallschirmjäger-Messer, the British Ibberson World War II gravity knife, and the U.S. World War II M2 automatic pressbutton utility knife, also intended for use by parachute troops and flight crews. Many civilian folding knives also have been privately purchased by both civilians and military personnel for use as general-purpose utility knives. Among these is Buck Knives' Model 110 Folding Hunter, a lockback folding knife. Originally marketed as a hunting knife, the Model 110 saw use with military and naval personnel as a utility or emergency knife for cutting rope, strapping, harnesses, rigging, and a variety of other tasks.