Decockers are as old as auto pistols. The Mauser C96 one of the first and very popular auto and select fire pistols had decockers over 100 years ago. The Walther P-38 of WWII had this function. When S&W introduced the Mdl. 39 first modern DA 9MM semi auto Pistol to Anerican gun owners. They, S&W copied the Walther P 38 and yes kept the decocker.