What are the origins of ‘knife hands’ in the military?

According to an old US Marine Corps legend, Colonel (The highest rank in the Army, pronounced ‘kerr-null’) Ishmael Knife lost his second favorite hand in the War of 1812. George Washington decided that instead of a medal, he would award Colonel Knife with the world’s first prosthetic hand. Washington whittled the hand out of the stump of a cherry tree in his backyard. He spent a fortnight contemplating which shape to fashion the hand into and finally decided that it should be straight out, fingers together and parallel to the forearm, to permit saluting, because if there’s one thing that General Washington enjoyed more than leading a good rebellion, it was being saluted.
COL Knife loved his new hand and decided to honor his favorite Marine, a young Lance Corporal. COL Knife pointed his “wooden gripper-grabber,” as he had lovingly named it, at the young Marine and said “Look here, leather neck. A good General is a mad dog. A great General is a warrior monk. But the best General takes care of his troops by any means necessary.” (He didn’t call him “Devil Dog” because that term was coined by the Germans and Germany was still called the Holy Roman Empire back then, but it can be assumed that COL Knife would have used that term were it in popular use).
COL Knife was instantly promoted/demoted to the USMC’s first Gunnery Sergeant and the gesture he had made towards the young LCPL was forever cemented in history as a “Knife hand.” It is symbolic of the love that a senior has for a subordinate. The fingers held out straight symbolize the straight and narrow path that the issuer of the Knife hand wishes the receiver to follow.
And do you want to know what happened to the young LCPL? Well he grew up to become General James Mattis. It is said that as the receiver of the world’s first Knife hand, only Secretary Mattis can give a true “Knife hand”, anyone else can only give a “knife hand” with a lower-case ‘k’.

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