The military issue combat knife is a rather common melee weapon in Fallout 3. It is affected by the melee damage bonus from Strength. It is one of the better low-level melee weapons, and can get around 3-4 strikes in V.A.T.S., even with a reasonable number of AP and a fast swing speed outside of V.A.T.S. However, it has extremely short reach, about that of an unarmed weapon. With 10 Luck, it becomes an extremely potent weapon that will critically hit almost once every 4 to 5 hits.
The combat knife itself has a single edge with a clipped point, with a serrated edge on the back. It is of the standard Bowie shape and it may have been modeled off the real-world KA-BAR military issue knife.
The combat knife has the highest value-to-weight ratio of any non-unique melee weapon in the game.
Stabhappy - Stabhappy shares all of its stats with Occam's Razor, but has two principle differences. Firstly, the raider that holds it respawns, allowing multiple copies to be obtained. Secondly, it deals an additional 50% damage to limbs.
Charon's combat knife - A unique, non-playable version used by Charon with identical stats to the regular version.
Trench knifeOperation: Anchorage (add-on) - The trench knife's stats are identical to the regular combat knife. The only difference is a unique "knuckle-duster" skin.
Sim version combat knife Operation: Anchorage (add-on) - A sim-only version of the weapon which differs only in health (essentially non-degrading).
Sim version trench knifeOperation: Anchorage (add-on) - A sim-only version of the weapon which differs only in health (essentially non-degrading).
Swampfolk combat knife Point Lookout (add-on) - A non-playable version of the weapon used only by Point Lookout'sswampfolk, this version has identical stats but has an object effect which inflicts an extra 35 damage per hit when used by non-player characters against the player. This damage ignores Damage Resistance and is independent of the condition of the weapon.