The personal weapon prohibitions under General Order #1 clearly state that you can't have "privately purchased firearms or ammunition". With the exception of switchblades knives aren't regulated, so most knife restrictions in the military have to do with state/local laws or unit SOPs. Here's an example; in my unit we used to issue Kabars until it came to our attention that Texas law sets a 5 1/2" limit for sheath knife blades (with certain exceptions). If you're in uniform and on duty, that 7" Kabar blade ain't a problem. However, if you're in civvy duds and clearly not engaged in hunting, fishing, military/law enforcement duties, that same Kabar is now an illegal weapon. To keep our young firebreathers out of trouble we switched the Kabars for 5" bladed pilot survival knives.
All fine and good in-garrison, but in a combat theatre of operations you're "on the clock" 24/7, so you can sport anything from a Randall bowie to a "horse traded" British issue golok. My young friend "Wheels" got introduced to khukuris while on a combat op with some British Royal Marines. They'd stopped one evening and set about constructing a hasty bivouac. "Wheels" is hacking away uneffectively with his Cold Steel SRK and turns to see his British teammates lopping wrist thick tree limbs like they were cooked spaghetti. The Brit lads explained that they'd been given the khuks by Ghurkhas during survival training. "Wheels" is not a slow learner, he now owns several khuks.
If I have to go again, and I might, you can bet the khuks I've accumulated will be "issued" out to my guys that don't already have one from last go around. I can always replace the khuks, but durned if I could replace a single one of them knuckleheads. Don't you worry, I'll keep one khuk for my own duffle bag.
Sarge