Some small departments allowed 1911s prior to the 1970s, but when a large department adopted the S&W Model 39-2 (9mm) in the 1970s, it really took off. Many departments followed suit with that model. Beretta's 92 also became a popular adoption in the late 1970s, but many departments held on to their revolvers till the 1980s. NYPD didn't switch till 1993. Glock was just getting very popular at that time, and soon dominated police adoptions.
I believe NYPD was the last major police department to adopt a semi automatic. they didn’t trust their police officers they thought it would be the wild wild west :-) my brother at the time was street crime/gun squad. For the rest of his career he was not fond of the Glock. he did carry it occasionally still with a Snubby in his waist band. He opted to carry two revolvers, his model 10 and five or six shot Snubby. Back then the projectiles were not very reliable regarding to expansion.
