What kind of handgun would an American police officer have used during the 1970s?

In the United States, each department sets its own requirements for what officers carry. In the city where I live, officers carry Sig 229s. In the county, officers carry Sig 226s. In another city near me, officers carry Glocks. In yet another city, officers carry H&Ks. All of those I mentioned, carry .40 S&W caliber. All that said, however, Glock is the most common.