The M9 Bayonet is a multi-purpose knife and bayonet officially adopted in 1984 by the United States. It has a 7-inch blade and is issued with a sheath designed to double as a wire cutter. It was designed and developed by Charles A. "Mickey" Finn at his R&D company, Qual-A-Tec. He later produced it under the Phrobis III name, filling a military contract for 325,000 units. Buck Knives was contracted to make 300,000 units and sold a commercial version under their own name. Finn's designs proved extremely popular, and were widely counterfeited and sold illegally by other makers. In 1986, Finn received US Patent 4,622,707, however, they continued to flow unchecked into the US from Asia and Mexico, cutting into legitimate sales.
Some production runs of the M9 have a fuller and some do not, depending upon which contractor manufactured that batch and what the military specs were at that time. The M9 bayonet partially replaced the older M7 bayonet, introduced in 1964. Although it has been claimed that the M9 may be more prone to breakage than the older M7; in actuality the M9 has a 20% thicker blade and tang and a 75% greater cross-sectional area of steel in the blade than the M7.
The M11 bayonet, or M11 EOD is a version of the M9 specialized for explosive ordnance disposal (EOD). It has some extra features, such as a hammer pommel, but uses the same blade and sheath as the M9.
There have been four main makes of M9's: Phobis, Buck, LanCay, and Ontario. Starting in 1987, Phobis subcontracted Buck, finishing up in 1989. It was around this time that Buck sold commercial M9s as well, which it did up to 1997.
LanCay got its first contract in March 1992 for 30 thousand knives; in 1994, there was another contract issued for about 100,000 improved M9 models. In 1999, a contract for 25,000 knives was split between LaCay and Ontario. Ontario Knife Company also participated in later contracts and is one of the current (as of 2005) contractors for producing them. These can be identified by the blades, which are marked "M-9 / ONTARIO / KNIFE CO / USA".