An M9 bayonet was a type of military knife used for combat. During Collateral Damage, Jack Bauer found an M9 bayonet among other weapons in Erno Tobias's wardrobe. He stashed the M9, along with two Gerber Guardian knives, in his Hawk's utility vest. Later he used the bayonet to kill three men including Jackson and Tyrell. (Collateral Damage)