Yeah, most militaries consider it peripheral or obsolete now. The SEALS do well as do the Foreign Legion, the Green Beret, and most special forces. A more recent development has been the Marine Corps' adoption of it's own martial arts system, "Marine Martial Arts." It's a system based on the principle of Fall-Back. Begin with your primary weapon, the rifle, and fall back to bayonet to knife to weapon of opportunity, etc. None of the techniques are original, just the ordering of training around what they are most likely to face. They maintain a good web-site at <<marinemartialarts.co>> There are also some good videos on youtube but they are somewhat dramatic.
Yeah, trying very hard to not get into that side of the disscussion.
It is actually very simple, all blade fighting fails into two camps cutters or stabbers. While you can do both with most, they tend to excel at one. The best cutter is considered to be the Bowie blade(which a Ka Bar is one), and the best stabber is the fairburn.
To be honest, most militaries do not really spend a lot of time training knife use. That said you should have seen the face of a copper when I explained how pointless his stab vest was against someone who knew how to use a knife. The SEALs among others train knife use in this regard.