It's a pre, pre-model 10...
...
S&W .38 1905 Hand Ejector (Military & Police) 4th Change. Estimated date of manufacture would be between 1918 and 1920.
It appears to be all original except for the stocks, which were made after the Second World War.
Given this gun's history within your family, I suggest that you get it "lettered." To do so you will need a snapshot of the gun, a full description including the serial number on the butt, and a check in the amount of $30.00 made out to Smith & Wesson. In exchange the company's historian, Roy G. Jinks, will research the original records (which are not computerized by the way) and send you a letter containing the details of what he finds.
This comprehensive document will contain an overview of the model’s history, followed by the details of your particular gun. This usually includes the caliber, barrel length, finish, and the exact date it was shipped from the factory, and to what distributor or dealer. If there are any special features they will be listed too. This information is often invaluable to both you and future generations.
Additional information on a historical letter will be found at the Smith & Wesson company website at:
www.smith-wesson.com