While I sharpen higher end Japanese kitchen knives on natural and synthetic waterstones, I generally sharpen outdoor/sporting & "tactical" knives on a 1" x 42" Kalamazoo belt grinder. It works very, very well! I can get a kitchen knife probably 85%-90% as sharp in three minutes on the grinder as I can with forty-five minutes on stones.
Sometimes it makes me want to throw all my water stones down an elevator shaft!