What is the Marine Corps' official knife?

Answer 1

The Marine Corps uses the K-bar. It can be seen on the Marine Corps Memorial strapped to the belts of a couple of those raising the flag. They are available very inexpensively through the exchange. Marines can also be issued one through their armory.

Answer 2

Traditionally, the Ka-Bar, although knives are personal purchases, and not issue items.

Answer 3

It's the M9 bayonet, and that's pretty much it. The Army doesn't issue combat knives, and soldiers who carry them purchase the knives on their own.