Combat knife

The Combat Knife, occasionally referred to as the Close Quarters Combat Weapon System in technical manuals, is a multi-purpose infantry-sized knife used by the United Nations Space Command.

Overview
The UNSC's multi-purpose combat knife has a 20 centimeter (7.9 inches) blade made of high carbon steel, an anti-flash non-reflective titanium carbide coating, edge coated for corrosion resistance and is 43.3 centimeters (1.42 feet) when sheathed. All UNSC troops are issued with a combat knife for field and utility usages, or in desperate situations, as a weapon. It can also be used around campsites when needed, and is balanced for throwing.

History
Knives have been used in battle almost since the dawn of warfare, first as a sharp piece of rock, and then metal proved effective during a period of time where projectile weapons were not readily available. The combat knife later branched off and became a sword, while others used daggers. For thousands of years, knives and swords have been a weapon of choice for soldiers. Even after the invention of the firearm, knives were still used as bayonets for close-quarters-combat and in event of enemys cavalry charge. Sabers were still issued in World War I. As war tactics shifted from trench warfare to attrition warfare, knives became last-resort weapons or simple tools used for cutting food up to making fire wood. By 2553, the UNSC still uses knives, showing that such an easily accessible and created weapon still runs strong even thousands of years later. Even the Covenant (especially Brutes) uses variants of the basic knife.

Appearances
A larger version of the combat knife, called the Machete, was intended to be used in the early Halo: Combat Evolved build, but was cut before it made it into the final game, replaced with the game's use of melee attacks from any weapon.

In Halo 2, a combat knife can be seen in game is on the lower backs of ODSTs.

The Spartan CQB chest permutation in Halo 3 multiplayer has a combat knife and its sheath attached to the left chest section. It cannot be drawn or used, and is purely ornamental.

In Halo Wars, Sergeant John Forge has a combat knife named "Lucy", which he uses to wound the Arbiter before killing him with an Energy sword. It also has a serrated edge like other combat knives as mentioned in Halo: The Fall of Reach.

In Halo 3: ODST, Edward Buck can be seen wearing a combat knife on his chest plate, which he uses to wound, and subsequently kill, a Jiralhanae Chieftain by stabbing him in the neck, afterwards casually flicking the alien's blood off of its blade.

In the Halo Legends episode The Package, Frederic-104 uses a combat knife distinctly different than previous incarnations. The blade itself is similar in terms of shape, but the handle has three circular holes cut out of it, most likely to reduce overall weight. Also the back edge is serrated. It should also be noted that they are stored in the shoulder pauldrons of his MJOLNIR Powered Assault Armor/Mark IV.

In the Halo: Reach world premiere cinematic, Emile-A239 is seen sharpening a special combat knife (which appears to be a Kukri) against his shoulder plate. Combat Knives will also be usable in-game to perform special extended animation sequences called "Assassinations" by holding down the melee button when behind an opponent.

Trivia

 * The ODST Action Figure, made by Joyride Studios, has a Combat Knife that can be held by the action figure's hand.
 * It was Frederic-104's trademark weapon, after the MA5B Assault Rifle.
 * In Halo 3 Concept Art for EGM, a SPARTAN-II is shown with a Combat Knife on his/her right leg, however this was just an aesthetic look for the ODST armor.
 * Also, in Halo 3 the chest armor permutation CQB has a Combat Knife sheathed on the left side of the breastplate, however this is also just aesthetic.
 * It appears that in Halo Reach, when performing a third person assassination animation, the provided knife on the SPARTAN-III's armor isn't used, but rather, a different one from out of nowhere.