It was to replace aging Smith & Wesson Model 10 for issuing to air crews and military police.The 9mm variant featured cylinder chambers bored to headspace the cartridge on the case mouth instead of the rim, using a patented spring moon clip to permit extraction of the fired case. 38 Special variant adding a lanyard ring to the butt and designating it the M108.
38 Special and 9x19mm Parabellum for some police orders. The U.S. 357 Magnum, though Ruger also built versions in. The Service-Six was normally chambered in. This was largely a marketing decision and an attempt to capitalize on the lucrative law enforcement service revolver market.
After a few months of production, Ruger renamed the fixed-sight version of the Security-Six the Service-Six or alternatively, the 'Police Service-Six'.
