Sgt. Rockwell never realised his gun could fire, and only used his bayonet.
Zig Zagged: Rockwell mounts his bayonet, kills an enemy with it, later unmounts it, and then is surprised at close range, where he uses his weapon's stock instead. After that his bayonet is mounted for the rest of the story, this encounter having made him rather paranoid.
Averted: No bayonets are used by the main characters.
Exploited: The characters hear they're going into an urban area. To mark them as Genre Savvy veterans, every single one of them immediately, in unison, mounts their bayonet. Or, if their weapon can't accept it, they duct tape their knife to the barrel.
The knives given to soldiers are not mountable on guns, to discourage them from charging into the enemy line of fire.
Instead of bayonet mounts, soldiers have underbarrel grenade launchers, flashlights, foregrips, or other such attachments that are more broadly useful.
"Now remember, soldiers: a bayonet charge only works if the enemy does not expect it. But when they don't, it tends to be pretty damn effective."
Reconstructed: Sgt. Rockwell waits until his enemies are occupied elsewhere, and gets his squad to charge them from the side or rear, suddenly and unexpectedly, with the support of other units on the flank. The enemy breaks and runs, not having expected such a sudden - or brazen - assault.
Played For Laughs: Sgt. Rockwell's bayonet is bigger than the gun it's attached to.
Played For Drama: Sgt. Rockwell is out of ammo, and so the bayonet is his only remaining weapon.