The Mark I trench knife is an American trench knife designed by officers of the American Expeditionary Force (AEF) for use in World War I. It has a 6.75 in (17.1 cm) double-edged dagger blade useful for both thrusting and slashing strokes, unlike previous U.S. trench knives such as the M1917 and M1918. The handle is made of cast bronze and uses a conical steel nut to hold the blade in place. The Mark I's blade was blued with a black oxide finish, the bronze handle was chemically blackened, with cast spikes on the bow of each knuckle. The spikes were intended to prevent an opponent from grabbing the knife hand, as well as to provide a more concentrated striking surface when employed in hand-to-hand combat.

Ka-Bar is the contemporary popular name for the combat knife first adopted by the United States Marine Corps in November 1942 as the 1219C2 combat knife, and subsequently adopted by the United States Navy as the U.S. Navy utility knife, Mark 2. Ka-Bar is the name of a related knife manufacturing company, Ka-Bar Knives., Inc., of Olean, New York, a subsidiary of the Cutco Corporation.