The Fighting Knife
I'm not going to try to teach you how to fight with a knife, only how to choose one that is right for you. Why even talk about a knife in this modern age of computerized guns, that see in the dark and around corners?  A knife won't jam, batteries don't run down, and they don't break like computers when you drop or bump them the wrong way, EMP and just plain water in the circuits!  Many times the knife is the only tool for the job. No matter what branch of service you are in, the lesson of the knife could be essential to your survival.  The blade length and shape,  handle length and shape, and balance are all important. I have made fighting knives for Elite and Special Op fighters for over 30 years! My knives have seen battle around the world. These are things I have learned, and recomend, You decide what's right for you!  Let me build a personal weapon, made just for you!
There are four basic ways to hold a fighting dagger. Shown above are the Hammer, Ice Pick, Fencing, and Reversed. Any knife that cannot be held in ALL the positions as shown is not a good fighting knive, and is limited in it's abilities.
As shown above, a fighting knife should have a square or rounded pommel, so that the finger or thumb can be placed for control pressure. The so called "Skull Crusher" pointed and other weird pommels are for the movies, not for battle.
Generally, you want the cutting tip to be as wide as possible, as in the spear point. The only exception would be to pierce some types of heavy materials. You want your pierce, stab or slash to be a blood letting experiance. This has been known since the Roman times, as most of their swords and daggers were spear points. The fact is, a spear point kills quicker! You don't want to piss off your enemy with a little 1/4 inch scratch, he might come back and kill you. A deep 1 to 1 1/2 inch wide cut will kill quickly.
The two photos above show the knife held in the reversed, ready, and  hidden position. This is desireable many times to be able to make a fast strike and the enemy may not even know you are armed. A fast strike to a vital target, neck, heart, or artery in the groin,, then a quick return to the hidden position guards your weapon from being defended against or being kicked from your hand. Your opponent my not even know what hit him.You can't do this with a Rambo knife from the movies. There are many fighting manuals that go into fast reverse and double reverse knife fighting. I would advise learning these techniques, rather than keeping the weapon foolishly held out in front of you. This is common in the streets and movies. Waving a blade around instills fear, looks cool in the movies, but is easily taken from you, or defended against.

Any knife with a bunch of deep grooves and saw teeth is a survival knife, not a fighting knife. If you stick some goon with one of those, you might just be leaving the scene without your knife. Those things just get stuck! The very best is a reverse tapered double edge spear point, that cuts its way in and out. If the knife is wider at the speer point than at the hilt or guard, like two of the examples above, it will cut its way out no matter what side pressures or struggle is involved.  Your weapon will stay where it is supposed to be, in your hand! It also cuts more flesh causing more rapid bleeding. Like a hunting arrow broadhead cuts an X shaped hole to bleed quickly, a twist on the knife when you withdraw it will make the wound bleed profusely. Loss of blood, loss of blood pressure, equals victory over your opponent. Gerber knives are the right style, just too narrow! Study the pictures above then you look at the so called fighting knives out there. You decide, are they really fighting knives?.
The photos above show a Manley Blade Merc Dagger in Hammer, Reverse Hidden, Reverse attack, and Ice Pick positions. This dagger blade is 8 inches long and a full 1 1/2 inch wide at the speer point. The handle has a coffin shaped end for finger or thumb and is balanced at the index finger so handling and reversing positions is not a clumbsy ordeal, but fast and accurate.

So How long should a fighting knife be? I have had people ask for a fighting knife with 12 inch blade or more. That is a short sword. The photo above showing the reverse hidden and ready position, shows the longest blade that can be used for fighting. Anything longer that will not clear your arm and clothing is a sword.

Below is a table, I made up,  based on the Cubit of a Man, showing my recommended maximum lengths based on your size. This is the Maximum and many times a much shorter blade is advisable.

Height        Cubit     Knife Blade
5'                 16.5             5.5"
5'6"               18               7"
5'10"             19                8"
6'2"               20                9"
6'6"               21               10"

As you can see, a 12" blade would only be a fighting knife for someone 7'2" or taller. I don't know of any of those tall guys  that are fighting with anything but a basketball in their hands. Anyone else, it's a sword, for pierce and slash only. Might as well be 3 feet long.

Note: For the Silent kill from under the diaphram to the heart, you need at least 7"