I think it's a RB, early postwar .38 M & P, with pre-war (1930s era) service stocks and the "speed hammer" of the late 1940-early 1950 era.
Looks like a M&P to me. Can we get confirmation on the caliber?
Charlie
Working on the caliber question as we speak....
-mgo
mgo,
Sir, that particular gun is an I frame. It was the predecessor to the J frame. It became known as the Model 32 Terrier in caliber's .32 and .38 S&W. The .38 S&W cartridge is shorter than the .38 Special. If you will look at the right side of the barrel, you will see the it say's .38 S&W CTG I believe, and not .38 Special.
Note the strain screw at the bottom of the grip frame. The J frame was introduced in 1950 and does not have that feature.
By the way, that particular gun is highly sought after in good condtion. There are others who will be along soon to inform you of the year and other features who are far more qualified than I.
Murphy2000
There is no way to measure scale from the pictures. Because of that even with a 6 shot cylinder we could not preclude that the gun wasn't a 6 shot Terrier. We know the 38 Special early I frame/J frames wouldn't have 6 shot cylinders.
However, the trigger guard shape and scale to the rest of the frame and the arc of the frame where the hammer is exposed is unmistakenly that of an M&P K frame.