Brian:

Double-edged, spear style blade.

Double-edge makes slashing in multiple directions easier without changing hand grip on the knife, and for cutting flesh on both edges of the knife if thrust into flesh.

Spear style blade makes deep thrusting easier for killing style attacks, and will penetrate multiple layers of clothing easier. The old style, and some of the newer bullet resistant vests could stop bullets, but some knives were able to penetrate them. Don't know about current bullet resistant vests as I have been out of that field for a long time.

Bountyhunter