I'm not sure if this question belongs here, but I'm curious why police departments started to adopt semi automatic pistols like glocks and sigs in the 70's and 80's and start to stray away from .38 and .357 revolvers? Semi auto pistols had been around for decades, but what changed? Was it cost? Round capacity? What was it?
I think I might have an answer to this where I could even provide reasonable citations... but we're veering into the 20 year rule. It should be said that the shift occurred later than the 1970s.
All of the above. A Glock 9mm has equal or greater power than a .38, is as least as reliable, and has a vastly higher capacity. With few exceptions that I know of, most popular semi automatic pistols prior to this had a 7 or 8 round capacity. I also haven't heard much of .357s being commonly used. Essentially, it was the ability to make a relatively compact (I'm looking at you, Hi Power) high capacity pistol that could match the reliability of revolvers.
This is in reference to US police departments anyway. From what I've seen a lot of Soviet States seemed to use low capacity semi automatics since the 40s and 50s on, even to today.
Lastly, I imagine that military surplus played a role as well. As the US military switched from a .38 revolver to the .45 1911, PDs were probably sold a lot of the revolvers at very low prices.
Followup question, is there a timeline somewhere of pistol adoption by police, for any agency?