sheaths and were sturdily made. During the Second World War, the Fairbairn–Sykes fighting knife was widely issued to forces such as the British Commandos, Royal Marines Commandos, Parachute Regiment, Special Boat Service and the Special Air Service. Though not a true "trench knife" per se, the Fairbairn-Sykes was used for similar purposes. US trench knives The first official U.S. trench knife adopted for service issue was the U.S. M1917 trench knife designed by Henry Disston & Sons and based on examples of trench knives then in service with the French Army. The M1917 featured a triangular stiletto blade, wooden grip, metal knuckle guard, and a rounded pommel. The M1917 proved unsatisfactory in service, and a slightly improved version, the M1918, was adopted within months. Despite this, the M1918 is almost identical to the M1917, differing primarily in the construction and appearance of the knuckle guard. Usable only as stabbing weapons, the M1917 and M1918 frequently suffered broken blades. Their limited utility and general unpopularity caused the AEF to empanel a testing board in 1918 to test various trench knives and select a replacement. This design was followed by the Mark I, which was designed by a board of U.S. Army officers to remedy certain deficiencies of the M1917/18.<ref name="CRO">Crowell, Benedict (1919), America's Munitions 1917-1918, Report of Benedict Crowell, Assistant Secretary of War (Director of Munitions) U.S. War Department, Washington, D.C.: U.S. Government Printing Office, pp. 88, 228</ref> Adopted in late 1918, with a blade profile patterned after the French Couteau Poignard Mle 1916 dit Le Vengeur, most Mark I knives were completed too late to see service in the trenches of World War I. During World War II, the Mark I was issued in 1942 and 1943 to airborne troops, Army Rangers, and Marine Raiders.Canfield, Bruce N., U.S. INFANTRY WEAPONS OF WORLD WAR II, Lincoln, RI: Andrew Mowbray Publishers, , (1994) The Mark I featured a full-tang design with a double-edged blade and a heavy bronze hilt incorporating a guard ostensibly shaped as a knuckle duster, though the latter was intended to protect the fingers and prevent the knife from being knocked from the hand while in combat rather than for use as a weapon. Despite their look, the spikes on the knuckles were also defensive in nature, meant to make it difficult for the enemy to grab the knife in combat Reflecting the savagery of hand-to-hand trench warfare, the