The M9 Bayonet is a multi-purpose knife and bayonet officially adopted in 1984 by the U.S. Army. It has a 7-inch blade and is issued with a sheath designed to double as a wire cutter. The M9 ...

How did the 15 inch sized bayonets of the 17th century evolve by the 21st Century into a combat gadget the size of a pocket knife, that is still in widespread use today with armies across the world?

Unfortunately, it just added to the growing collection of other "tools" the soldiers needed to carry, which already included things like a bayonet, knife, and can opener (to open canned food).