I think by now, most of us are on the same page about always being armed with something no matter the social rules to the contrary. And even if that means you will only have a knife, at least you will have something. And something is better than nothing. When I teach knife, my students realize that inside of ten feet, a knife man is on even ground with any other man regardless of size or weaponry. Big guy versus small guy is not a problem for the small man with a knife. Gunman versus knife man is not a problem if the knife man takes the initiative. It is understood that the knife man must have a certain level of animal violence to call up as killing that way is very personal. But we move on. When do we rely on the knife?
1). Primarily, you use the knife when you don't have your pistol available. This may be that you simply could not bring it with you, or because it was lost or disabled. It is always easier to shoot someone in the face than to stab them. There are times when the pistol will simply not be available, but you can always, even behind the security screen at an airport, find something that you can stab with. While I prefer good quality blades, but at the very least, once you land, you can purchase a knife locally and carry it with you everywhere regardless of what the rules may be. Knives are bought for cash, used as necessary and easily discarded if necessary.
2). You use the knife in the same events you would use your pistol. Against a gun pointed at you. Against a gun being brought to bear on you. Against a big enemy that you cannot defeat physically...even if he is unarmed. Against a number of enemies attacking you, even if they are unarmed. The knife is fueled by movement. I teach my students how to avoid the muzzle, draw and stab the neck of a rifleman at ten feet with astounding success. If you cannot move for whatever reason, then maybe this is not for you. The use of the knife is aggressive avarice.
3). Most knife training is defensive in nature and involves knife sparring. This is fine for learning the knife, how to move, and how to use the blade. But like the use of the pistol, Americans are excessively focused on being fair, and what the courtroom might say and such combat irrelevancies. Look at the image at the lead of this article. This is not some fantasy dreamed up in the mind of a gun writer. This is real, this has promised to come and kill you, and this has shown to keep its word in the middle east and in Europe. And since Hillary has a real chance of winning the election in a few months, this will in fact be coming to your shores paid for with the money your government takes from you every paycheck.
When you come face to face with this, are you really going to be worried about what the law will say about your use of a knife? If you are, you are a fool and deserve to die while deciding on your course of action.
4). There is nothing fair about using a knife. In fact, when I teach knife I teach deployment in surprise, and off sides stabbing. Think of how a bad guy in the movies would use a knife and you will get the idea. Sucker Stabbing 101 (the same course as Sucker Shooting 101...but with knives). I teach stabbing over slashing. Slashing is defensive, but I am not concerned with defense here...I am concerned with attack.
5). So I teach stabbing as the preferred line. I teach attacking the face and neck with those stabs and would prefer to avoid the body. I avoid the body due to the presence of armor, IED vests, as well as clothing which may deflect or nullify a stabbing attack. Also in my experience, the result of a stab to the torso may not be as quick as one to the neck. And this is not just one stab, unless you stick it well...then it is. And if you stick it well, crank the blade back and forth making the wound worse, the shock greater and the resulting response quicker. I prefer reverse grip as even the weakest soy-eating emo-man will have enough physical strength to make this work. One of my students related a story of his use of this overseas and actually broke a bad guy's collarbone with the downward stab.
Recall the earlier discussion: This is not martial arts.
6). To facilitate stabbing, select a knife capable of a stabbing attack. Avoid fancy twirly knives designed to slash. I would not choose a Spyderco Civilian, nor any sort of Kerambit. Better would be even a Fairbairn knife from WW2...or a sharp Phillips screwdriver that you can stab with. How long will it take for the terrorist to die when stabbed? I have no bloody idea. It depends on many factors, but I think he will die faster with a stab than a slash. And I think we need to realize that this is not a poke from a far and then a lengthy observation session waiting to see what happens. This is a powerful physical attack with everything you have driven repeatedly into his body with every ounce of ill will and hatred you can muster.
Look at the attack here.
This guy is attacking the body of an unarmored adversary. Our concerns preclude that targeting so we go for the neck, but this is indicative of the intensity necessary. Forget "defense", think "attack". Forget slashing the limbs, attack and stab the neck and face. Forget survival and disengagement, you are there to kill the terrorist.