The U.S. Army adopted the M3 fighting knife as a replacement for the Mark I in 1943. The Mark I required strategic metals to produce and was too costly to place into mass production, and had been criticized as being unsuited to more modern styles of hand-to-hand knife fighting. As the U.S. "Catalog of Standard Ordnance Items" of 1943 explained: "The Trench Knife M3 has been developed to fill the need in modern warfare for hand-to-hand fighting. While designated for issue to soldiers not armed with the bayonet, it was especially designed for such shock units as parachute troops and rangers." The M3 was first issued to U.S. Army soldiers in 1943, with the first knives going to elite units such as airborne troops and the U.S. Army Rangers. Despite being designed for hand-to-hand warfare, the M3 did not receive universal praise as a fighting knife upon issue to combat units. While well-balanced (some paratroopers and rangers mastered the art of using the M3 as a throwing knife), the M3's blade was criticized as being too narrow for rough usage, particularly for utility tasks such as opening ammo crates and food tins, while its edge was found to be somewhat difficult to sharpen. The blade's secondary edge was also criticized as being too short, limiting the knife's utility when used for backhand slashing strokes. Many features of the M3 were incorporated into the M4 bayonet for the M1 Carbine, the M5 bayonet for the M1 Garand, the M6 Bayonet for the M14 rifle, and finally the M7 bayonet for the M16 rifle. The M3 knife and all of these bayonets fit in the M8A1 scabbard, officially designated as the "Scabbard, Bayonet Knife, M8A1," with the National Stock Number (NSN) 1095-00-508-0339.