Combat knife in the context of "Hand-to-hand combat"

A knife (pl.: knives; from Old Norse knifr 'knife, dirk') is a tool or weapon with a cutting edge or blade, usually attached to a handle or hilt. One of the earliest tools used by humanity, knives appeared at least 2.5 million years ago, as evidenced by the Oldowan tools. Originally made of wood, bone, and stone (such as flint and obsidian), over the centuries, in step with improvements in both metallurgy and manufacturing, knife blades have been made from copper, bronze, iron, steel, ceramic, and titanium. Most modern knives have fixed or folding blades, with styles varying by maker and country.

Knives can serve various purposes. Hunters use a hunting knife, soldiers use the combat knife, scouts, campers, and hikers carry a pocketknife; there are kitchen knives for preparing foods (the chef's knife, the paring knife, bread knife, cleaver), table knife (butter knives and steak knives), weapons (daggers or switchblades), knives for throwing or juggling, and knives for religious ceremony or display (the kirpan).

A fighting knife has a blade designed to most effectively inflict injury in close-quarters physical confrontations. The combat knife and the trench knife are examples of military fighting knives.

Fighting knives were traditionally designed as special-purpose weapons, intended primarily if not solely for use in personal or hand-to-hand combat. This singleness of purpose originally distinguished the fighting knife from the field knife, fighting utility knife, or in modern usage, the tactical knife. The tactical knife is a knife with one or more military features designed for use in extreme situations, which may or may not include a design capability as a fighting or combat weapon. Since World War I, the fighting knife in military service has gradually evolved into a dual-purpose or "fighting-utility" knife, suited for both knife fighting and utility roles. As a consequence, the terms "fighting knife" and "tactical knife" are frequently employed interchangeably.

A trench knife is a combat knife designed to kill or incapacitate an enemy at close quarters, such as in a trench or other confined area. It was developed as a close combat weapon for soldiers attacking enemy trenches during the First World War. An example of a World War I trench knife is the German Army's Nahkampfmesser (close combat knife).

During the Second World War, the trench knife, by this time also called a combat knife, was developed into new designs. On the German side, the Nahkampfmesser and associated knives were widely issued to the ordinary soldier for combat and utility purposes, while Allied armies mostly issued trench knives to elite infantry units and soldiers not equipped with the bayonet.

Ka-Bar (/ˈkeɪ.bɑːr/; trademarked as KA-BAR) is the combat knife adopted in 1942 by the United States Marine Corps as the U.S. Marine Corps utility knife, Mark 2.