During WWI and WWII, the infantry would use shovels as weapons and to dig trenches. I bet they really dig that weapon!
Infantry Shovels
Explanation
Explain Bear
Alright listen up, genius. The joke is that the infantry used shovels, and the word "dig" is used in two ways. "Dig trenches" means literally using the shovel to dig, and "really dig that weapon" means they liked the weapon. It's a pun, you walnut.