Smith & Wesson Model 12 - Wikipedia

In 1953, the United States Air Force (USAF) ordered a variant of the S&W Military & Police Airweight with a two-inch barrel and aluminum cylinder to be issued to US Air Force flight crew members, called the Revolver, Lightweight, Caliber .38 Special, M13.[1][2] Some 40,000 Smith & Wesson M13 revolvers were produced.[2] After persistent reports on cylinder and frame failure with the M13 and its counterpart, the Colt Aircrewman, the Air Force attempted to remedy the issue by issuing a dedicated low-pressure .38 cartridge for the weapons—the Caliber .38, Ball, M41 round.[3] However, after continued negative reports, Air Force officials decided that the revolvers were not suitable for issue, and the model was withdrawn from service, all but a few examples being crushed or destroyed.[2]

A civilian model of the M13 was released in 1953, called the Military & Police Airweight. This designation was changed in 1957 to the Model 12 Airweight.[1] The Military & Police Airweight initially used both an aluminum cylinder and frame, and weighed only 14.5 ounces.[1] The aluminum cylinder proved insufficiently strong to withstand continued firing with standard .38 Special cartridges, and in 1954, S&W changed over all new production Airweight revolver cylinders to steel, increasing the weight to 18 ounces.[1]

The Model 12 variants—12-1, 12-2, and 12-3—used a narrower hammer[4] and had an aluminum grip frame that was 0.08-inch (2.0 mm) narrower than the standard steel K-frame.[1] The final version, the Model 12-4, used the standard frame dimension[5] of the other K-frames. It also featured a rounded butt.

• Pre-Model 12: predates model number markings. It has an alloy cylinder and will be a five-screw design with four sideplate screws and a screw in front of the trigger guard.
• Model 12 (1957):
  • -1 (1962): Change extractor rod to LH thread, eliminate screw in front of trigger guard
  • -2 (1962): Front sight changed from ⁠1/10⁠″ to ⁠1/8⁠″
  • -3 (1977): Gas ring on yoke to cylinder
  • -4 (1984): Change frame thickness to the same as all K-frames[citation needed]