The Commando Dagger or fighting knife has a double edged blade.

The FS Knife was developed by William Fairbairn and Eric Sykes based on concepts which the two men conceived  prior to World War II whilst  serving in the Shanghai Police.

The fighting knife was made famous during World War II when it was issued to the British Commandos, Airborne Forces, the SAS, Home guard,  and many other units the issuing was most widespread in anticipation of the  Normandy landings .

A weapon with a tapering blade optimised for thrusting.

The F-S knife is capable of being used to inflict slash cuts  when its cutting edges are sharpened . The Wilkinson Sword Company produced the knife with minor pommel and grip variations.

The F-S dagger is largely associated with the British commandos and the US Office of Strategic Services (OSS) and Marine Raiders they based their issued knife on the Fairbairn-Sykes), among other special forces / clandestine / raiding units. It features in the insignia of the British Royal Marines, the Belgian Commandos, the Dutch Commando Corps, founded in the UK during World War II, the Australian 1st Commando Regiment and 2nd Commando Regiment, and the United States Army Rangers, both founded with the help of the British Commandos.

The 3rd Canadian Infantry Division who landed on Juno Beach on “D” Day and  the 1st Canadian Parachute Battalion who jumped and fought there carried FS daggers .

The first batch of fifty F-S fighting knives were produced in January 1941 by Wilkinson Sword Ltd after Fairbairn and Sykes had travelled to their factory from the Special Training Centre at Lochailort in November 1940 to discuss their ideas for a fighting knife.The F-S fighting knife remains in production because of continued use in hand-to-hand combat situations around the world. The F-S fighting knife was designed exclusively for surprise attack and fighting, with a slender blade that can easily penetrate a rib cage. The vase handle grants precise grip, and the blade’s design is especially suited to its use as a fighting knife. Fairbairn’s rationale is in his book Get Tough! (1942).  “There is no more deadly weapon than the knife” in close quarter combat . In choosing a knife there are two important factors to bear in mind: balance and enthusiasm. The Fairbairn-Sykes was produced in several patterns. First pattern knives have a 6.5 in (17 cm) blade with a flat area, or ricasso, at the top of the blade which was not present on the original design and the presence of which has not been explained by the manufacturers, under the S-shaped cross guard. Second-pattern knives have a slightly longer blade (just less than 7 in (18 cm)), 2 in (5.1 cm)-wide oval cross guard, knurled pattern grip, and rounded ball, and may be stamped “ENGLAND” (a US legal requirement when importing the surplus knives after WWII, as they had to show the country of origin) on the handle side of the cross guard. Some may also be stamped with a “Broad Arrow” /|\ British issue mark and a number (e.g., 21) on the opposite handle side of the cross guard. Third-pattern knives also have a similarly sized seven-inch blade, but the handle was redesigned to be a ringed grip. This ringed grip is reputed to have distressed one of the original designers as it unbalanced the weapon and made harder to hold when wet, but it was used by the manufacturers as it was simple to produce and could be cast from a cheaper and more plentiful alloy instead of using up scarce quantities of brass stock which were, of course, required for ammunition casings and other such vital applications. William Rodgers, as part of the Egginton Group, now also produce an all-black “sterile” version of the knife, which is devoid of any markings showing maker for NATO use. The length of the blade was chosen to give several inches of blade to penetrate the body after passing through the 3 in (7.6 cm) of the thickest clothing that was anticipated to be worn in the war, namely that of Soviet greatcoats. Later production runs of the F-S fighting knife have a blade length that is about 7.5 in (19 cm). In all cases the handle had a distinctive foil-like grip to enable a number of handling options. Many variations on the F-S fighting knife exist in regards to size of blade and particularly of handle. The design has influenced the design of knives throughout the many decades since its introduction. Copies[edit] Because of the success of the Fairbairn-Sykes Knife in World War II and in the wars in Korea and Vietnam, many companies made their own versions of the F-S fighting knife, such as the 1966 Gerber Mark II. Almost two million of the British knives were made. Early production runs were extremely limited and demand was high, with many British troops attempting to buy their own. OSS version[edit] Representation of the knife used by the OSS with its distinctive scabbard. Collection of the CIA Museum. The OSS Stiletto was a double-edged knife based on the Fairbairn–Sykes fighting knife. It was so admired that the US military created several other fighting knives based on it. The US Office of Strategic Services’s knife manufacturing bid was approximately one-fifteenth of the British equivalent, but the US version of the knife, manufactured by Landers, Frary & Clark, of New Britain, Connecticut was improperly tempered and inferior to the British F-S Fighting Knife in materials and workmanship. Its reputation suffered accordingly.[3] A total of 20,000 units of the OSS version were produced. The OSS dagger was officially replaced in service in 1944 by the US M3 Fighting Knife.[6] The scabbard for the OSS Stiletto looks like a pancake spatula but this is because of the design so that can be worn high or low on the belt, or angled either left or right. In theory this gave a very adaptable mounting system, but the sheet metal was like a knife itself, especially to a parachutist. Other knives by Fairbairn[edit] General Robert T. Frederick of the Devil’s Brigade (First Special Service Force) is credited with a similar weapon, the “V-42 Commando Knife” V-42 Stiletto, itself a derivation of the F-S design. The V-42 was manufactured by W. R. Case & Sons Cutlery Co. in the US circa 1942-43 and is distinguished mainly by its markings and the presence of a small, scored indentation for the wielder’s thumb, to aid in orienting the knife for thrusting. Fairbairn has been given full or partial credit for the Smatchet and several other fighting knives.