From its introduction in 1955 until its production ended in 1982, Smith & Wesson's first generation of single-stack nines saw only minor changes. In 1957, it became the "Model 39", with some improvements to the extractor and safety lever. Then in 1971 further design changes to the extractor and feed ramp rated the "Model 39-2" nomenclature.
Starting in the early Eighties, Smith began marketing a whole new generation of its pistol, and added a third digit, so the aluminum-framed Model 39 with its carbon-steel slide became the Model 439, and the same gun with a carbon-steel frame and slide was the 539.
In 1984, Smith leveraged its experience in working with stainless steel revolvers into an all-stainless version of its 9mm pistol: The Model 639. This was something of a novelty at the time, since Smith was one of the only manufacturers of the era who sold stainless self-loaders that weren't plagued by galling issues between the frame and slide.
The most notable change in the mechanicals of the Second Generation pistols was the addition of a firing-pin safety that rendered them more drop-safe. They also had optional ambidextrous safety levers, a checkered backstrap, and the adjustable rear sight on models so equipped was protected by sturdy "wings" rendering it less likely to be knocked askew when carried in a duty holster or dropped.
The first few hundred 639's off the line had a short, wide extractor before it was changed back to the proven type found on the 39-2. After the first year of production, 1985 and later guns had a square, hooked trigger guard of the sort that was popular in the '80s. Those two factoids (plus the "TAA" serial prefix) date the 639 in the pictures to 1984.
Notable Hollywood 639 toters include The A-Team's "Hannibal" Smith and Harvey Keitel's Mister White in Reservoir Dogs.
Production of the Model 639 continued through 1988, when it was replaced by its heavily-revised Third Generation successor, the Model 3906.
The pictured pistol was acquired from Indy Arms Company for four fifty in summer of 2023.