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.
