Probably a model 5906 police trade-in; if much older, may have been the previous similar model, the 659. The 659 had two separate grip panels, 5906 had a one-piece wraparound grip.
Solid pistols, a bit on the heavy side, which is a plus for shooting but a minus for carrying. Usually quite reliable, but like any other pistol, there will be loads that it doesn't "like", both for reliability and accuracy. The .40 later killed-off most of the 9mms models in this frame style, but they were quite popular in the early "wondernine wars" when police departments had just begun converting from revolvers to autoloaders in the 80s. I think the S&Ws were (along with the alloy-framed 459/5904) the only double-stack (high capacity) American-made autoloaders available at the time, and pretty much the only game in town if you wanted stainless-steel construction.
Run a Google search for "S&W 5906" or "S&W 659" and click the Images tab to compare photos.