All the US company entrants failed in the XM9 trials. Of the US companies the S&W entrant lasted the longest, only being rejected close to the end when they found a cracked frame that was not experienced with the Beretta or Sig entrants, which statistically tied.There's no doubt some troops found the .45 ACP's recoil objectionable (although it was more an issue of magnitude than sharpness), and the lower recoil of the 9mm Luger helped in that regard, particularly in range qualification.
But a US 9mm Luger service pistol was envisioned as far back as 1947 and the 1949 trials included the 9mm Lightweight Colt Commander, the S&W X100, which became the Model 39, and a short slide allow version of the Browning Hi Power.
All of them would have offered the same reduced recoil and to carrying degrees increased magazine capacity in a handgun with a grip that would fit a larger percentage of troops than the eventual M9. The reality simply was we had plenty of serviceable 1911s in the decades following WWII period and the whole idea was eventually dropped.
Interestingly all of the above were excellent designs.
The S&W 39 enjoyed good commercial success and led to the S&W 59, one of the first "wonder nines".
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The Colt Commander also enjoyed a great deal of success and is still one of the more commonly cloned semi auto pistols.
The short slide alloy frame variant of the Hi Power was revived by FM in the 1990s after they discontinued their license with FN, and is currently being produced by Girsan.
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And of course the 1911 Lightweight commander was not only sold by Colt with success, but has also been marketed by Ruger, Kimber, and others.
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They redid the test again in 1988 and the Beretta won a second time.