Since I used to be in R&D while in the Army, I sent for the Army document that is supposed to detail the reason the Army wanted a new bayonet (to replace the old M-7). The need is identified by the following statement, "A need exists for a high quality multipurpose knife/bayonet which can be used by the combat soldier to defend himself in close combat with the enemy and as a multipurpose knife to aid in performing daily field tasks; when used with its scabbard, it becomes an effective wire cutter. The priority of design functions are: (1) bayonet, (2) combat knife, (3) field craft knife, (4) wire cutter, (5) limited saw capability, (6) mine probe (anti-metallic), and (7) civil disturbance deterrent. It was proposed to have blade steel similar to a sportsman's knife (I think it ended up with 420J series stainless steel), be sharpened in the field, retain an edge, cut soft wire, have a saw to cut light sheet metal and plexiglass, be capable of attachment to the M-16 series of rifle, have a sharpening device as a component, have little to no weight increase over the M-7 bayonet, and have weight, handling, and balance characteristics required for hand-to-hand knife fighting. Some other features were considered such as a hollow handle.
Recently a product improvement program was undertaken to improve the M-9 such as eliminating the blood groove and the sharpening stone on the sheath.
If you've ever carried or even handled an M-9, you know it is very heavy, more than doubling the weight of the M-7 w/sheath. The sharpening stone embedded in the back of the sheath had a cover, but when removed, the abrassiveness of the stone wore holes in your BDU's so it was removed in the improvement. I would rather take the weight of the M-9 and split it between the old M-7 as a bayonet and furnish my own combat knife!
