Factual correction:
The 40 was designed on the 10mm Auto frame, which was designed after the Florida shooting in the 1980's. The
FBI ran tests and determined that more penetration would have been a solution to that crisis (shooters were not on anything, took multiple hits without going down), and that the solution to their problem was 10mm Auto. Well,
FBI agents kept complaining about recoil / requesting downloaded rounds, ammo
mfg companies started producing 10mm "light" loads, and eventually s&w determined that if they were loading them light, they might as well cut the case down so it would fit into a 9mm frame. And the 40s&w was born.
That's your ultra-short version.
Nothing to do with 45ACP or female officers not "handling" 45ACP. Fact of it is, 40s&w and 45ACP at least in modern loadings, have almost identical performance in terms of muzzle energy. Recoil is only slightly different between the two - take the same gun and swap calibers (keeping bullet weighs as close as possible), you will have a hard time distinguishing a difference.
Also the standard cartridge of the time prior to the 10mm (
FBI) was the 9x19 luger, not the 45
ACP.
As a last note, with modern ammunition there is very little difference between the stopping power of 9x19 luger, 40 s&w and 45
ACP. I know, you don't believe me. They all have very similar penetration depths and permanent wound cavities. I've seen the calibrated ballistic gelatin of many of them. There are minute advantages to each, that apply in unique situations. There are a few select situations where a defensive loaded 9x19 would stop a perp where the same 40-45 bullet would not have, believe it or not. Reality is though, because they are close enough - a round that would kill or stop a perp with a 45, would do it with a 40, or a 9. None of them accommodate misses, and none of them would "kill or stop" a man better than the others if you miss a vital area by more than just a few inches. Accuracy, speed of first shot, control, repeatability matters more than the strength of the caliber itself. Note: I'm not talking ball or
FMJ rounds. Defensive rated ammunition ONLY.