Knife
From Exterminatus Manual
++Weapons++
The standard issue combat knife is the most basic weapon of the Space Marines, consisting of a simple blade made from a dense metallic alloy attached to a hand grip. The alloy itself is extremely durable and is known to be able to hold a edge for much longer compared to a similar steel knife.
It is the Space Marines weapon of last resort, although don't be fooled by its simple appearance, in the hands of these genetically engineered warriors it is more than capable of cutting clean through a man's arm. It is sometimes referred in jest as the "butter knife" due to its shape.