The leaning towards 9mm started with the United States House of Representatives. In 1978, the Surveys and Investigations Staff of the House Appropriations Committee examined defense handgun and ammunition requirements, reporting over 25 different makes, models and types of handguns in the defense inventory with 140 different cartridge types catalogued to feed them. Much of this problem came from ammunition left over from previous wars, including WWII and the Korean War. Congress declared that it was inefficient to have so diverse a selection of handguns, because it would cause problems in the areas of supply, maintenance, repair and ammunition stocking problems.
The House Appropriations Committee sought economies and efficiencies from handgun standardization, encouraging a defense transition plan "to achieve a standard handgun". By 1980 Army Armament Research and Development Command was conducting handgun and ammunition studies. It was immediately evident that there was far to many types of ammunition and they were reduced to only 30 (discontinuing 110 types). The handgun studies objective was to determine the minimum number of types of handguns needed for essential service. Another factor, the 9mm worked out well because there was a growing need for a smaller round, with less recoil, a lighter frame and more shots, because of all the women entering the armed forces. The women's small hands were a problem because they were being issued .38 Special revolvers to fit their hands and to lower the recoil. And so, for all of the above reasons, the faithful old M1911 .45 ACP was flung out the door, some of the frames having seen 40 years of service! In its place came the Beretta m9, military version of the Model 92 and the Sig Arms M11, the military version of the Sig P228.
Beretta m9Sig Sauer P228