Sturm, Ruger, and Company opened its doors for business in 1949, with one product - a semi-automatic 22 caliber pistol. As the company continued to grow, so did its product line, and around 1970 (various sources claim 1970, 1971, and 1972) it produced its first double action revolver, dubbing it the Security Six.
Also known as the Model 117, the Security Six was poised to compete with Colt and Smith & Wesson as a police gun. In the early 1970s, revolvers still ruled, and in a "serious social situation," double action is a better choice than single action, because it's easier to use quickly.
While the double action pull of the Rugers I've tried is usually poor (heavy and inconsistent), the lower price and overall ruggedness of the newly-introduced Security Six were appealing to many.
Ruger followed the Security Six with some variations on the theme, known as the Speed Six (Model 207) and the Police Service Six (Model 107). While externally different in some ways, both of these models are mechanically identical to the Model 117, AKA Security Six.
The specimen seen above features a four-inch barrel and adjustable rear sight, and wears Pachmayr finger-groove grips. Stamped on the left side of the barrel is the obligatory Ruger "read the manual" warning above its company name. Just aft of that is a stamped proof mark.