Tomahawk. Best of both worlds... sharp, but with a lot of weight like a blunt object. A proper fighting hawk also has a sharpened spike on the back, so you can hit with either the main edge or the spike. Back of the neck, base of the skull is good. The spike might be able to get through a helmet, I dunno.
Still, whacking the head or the neck, I wouldnt expect it to be totally silent. A skull being chopped into, or crushed makes a rather distinct and loud noise, even if the person does not utter a cry. And they could still make a sound vocally. I'd think about the only way to prevent this would be a complete beheading, but the likely hood of taking someones head clean off is doubtful.
Theres a quote I like to use a lot, its from custom knife maker Mick Strider (Who is also Co Founder of the production company Strider Knives), he said it at BladeForums in a discussion there on this very topic... at the end of a long post on technique with a knife: "P.S. A framing hammer works better than a knife
" and I'd think Mick would know.
Still, theres that icky pop/crunch sound, and the possibility of an outcry.
As for knives,
The problem these days with targeting the kidneys, is that soldiers wear so much gear, and a great deal of it is across their backs, you're more likely to stab his kit, than to stab him. WHich will slow you down for a second as you go "***?" and give him a window.
When you attack from behind, weak hand comes around his side, over the shoulder, slamming up under his chin, jamming his mouth shut (like a reverse chin-jab), and your thumb and index finger pinc his nose closed. Force his head back, and to towards your arm, and jam your knife into the exposed side of his neck, and pivot it forwards, through the front of his neck... more tearing than cutting. Should take out all the lovely blood veins, sever his wind pipe, and destroy his vocal cords. He's still going to gurgle and sputter, perhaps loudly... but maybe keeping your hand over his nose and mouth until he's gone, will minimize that. Lots of blood, on you, in your eyes, in your mouth and nose. Icky.
And this is only after you've managed to sneak 20 yards without making a sound, breaking a twig, or breathing much, so that you can sneak up on his sorry ***, just to do that.
A nice silenced weapon, with a sound-insulated shroud over the action, and shooting them in the head is probably the best way... and still, theres the noise of the bullet impacting the skull to deal with.
Interesting hypothetical to think about... but, not something I'd like to do.
For some ideas of how much noise people make when sustaining these types of injuries, check out ogrish.com or rotten.com, some-place like that, which will have videos of third world executions and similar brutality. Theres one on Ogrish of a Russian soldier standing on a guy, and cutting his throat out... the guy makes a damn lot of noise, even with a similar cutting action to what I described being done on him. :shivers: Icky. Icky.