From the first meeting, it was clear that the army wanted the Beretta Model 92 as it's new "Personal Defense Weapon (PDW)" to replace the 1911A1 in service. All of their Requirement documents were written to get the M92 and not anything else - and every time Colt or H&K or S&W or SIG sent one of their pistols in for the "competition", the Requirements would be shifted more towards the Beretta.
We Marines were not thrilled about the new pistol and even less thrilled about its 9mm caliber. Ever study of wound ballistics indicated that .45 kills reliably but the 9mm just wounds when military hardball is used. As one wag put it - "are we going to the same caliber that the Germans lost two wars in a row with?"
The army was hard over on the subject, so no surprise, the Beretta won and became the M9 and the rest, as they say, is history.
While any sane and experienced combatant whose life has depended on a pistol would prefer a .45, among the 9mms available, the SIG is a quality weapon.
USMC wanted the new Colt Rail Gun M45A1 until the frames started cracking. Now they’re keen on the Glock 19 9mm. The cartridge wars are OVER. 9mm is just about on par with the .45 and you get a lot more rounds to play with. The 9mm has never “just wounded”, but you just can’t tell people that the 9mm has killed more people than the .45 ever will.
It’s not even the handgun itself that improved performance over the M92, apparently... It’s the “XM1153 Special Purpose ammunition” (hollow points) that may have been the primary performance improvement.