In the early 90s the 40 S&W rose rapidly in law enforcement based on the FBI pick of it over the 9mm.
To be a bit more precise, the FBI did not pick the .40 over the 9mm. They picked the .40 over the
10mm.
Despite performing exactly as it was spec'd to do, the FBI decided the 9mm "failed" during the Miami Shootout, and cast about for a "better" round. The 9mm was "not good enough"... and after the dust cleared and the fingerpointing was mostly over, they chose the 10mm. (interestingly enough, during this period the FBI re-authorized the carry of the .357Mag and the .45ACP)
The FBI chose the 10mm, and an S&W pistol for it. HOWEVER, the 10mm, and that S&W turned out to be too much gun. The round was too powerful, and the pistol too big. Too many agents could not make the needed qualifications with it. The FBI's solution to this was to request a reduced power load in the ammo, (which came to be called the "10mm Lite" by some folks) and cast about for a different pistol.
As they were looking, along came S&W (who had been doing their own looking) and said "we have this new round, a .40, that does everything you are asking for, AND fits in 9mm frame guns!" The FBI grabbed it with both hands and ran with it. A little later many of the police groups across the country adopted it, as well.
So, the FBI replaced the 9mm with the 10mm, then replaced the 10mm with the 10mm Lite, then replaced that with the .40S&W.
I don't know for sure, but I heard that the FBI has gone back to the 9mm. Wouldn't surprise me, if they had...