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S&W's first hammerless handgun was introduced in 1887 in .38 S&W and 1888 in .32 S&W.
The .32 and .38 Safety Hammerless, also called the New Departure or Lemon Squeezer, were made right up to World War II.
They were EXTREMELY popular, and after WW II there was a call to reintroduce them. S&W wanted to drop all of the old-style guns, though as well as bring out a small revolver chambered for the .38 Spl., so the J-frame was introduced in 1951 with the Chief's Special, with the Centennial coming out in 1952.
Not long after that S&W began getting calls for a J-frame with a shrouded hammer. Colt had been offering a screw on shroud for the Detective Special for some time (I had one for awhile, neat, but I just couldn't get used to the Colt controls after having S&W for years), so the Model 38 Bodyguard Airweight was introduced in 1955.
Interestingly, it's one, if not the only, time a "lightweight version of a gun was introduced before the steel-framed version (the Model 49 Bodyguard in 1959).