You are looking at an original WWI US Mark One 1918 Trench Knife by Landers, Frary, & Clark - L.F. & C.
The Mark One also known as the "1918 Brass Knuckle" knife, has a double edged dagger blade. The handle is made of cast bronze, which used a conical steel nut to hold the blade in. The handle has spikes formed on each knuckle. The spikes were intended to prevent an opponent from grabbing the knife hand, as well as to improve the striking power. The knife is in excellent condition overall. The iron skull-crusher retaining nut at the back of the handle is intact and has never been ground down.
This is a beautiful example of a scarce American fighting knife. The Mark One in this condition is very rare, so make an offer quick if you're interested!