Alan is correct. The MSHP revolvers were .38 Combat Masterpiece units with the special order 5" barrel supplied by the factory. Records seem to indicate that at least 367 units were assembled, with 365 shipped to Shapleigh Hardware, in St. Louis, Missouri, for delivery to the State Highway Patrol. There were a total of four shipments, beginning on June 13, 1952, and ending with a shipment of 30 units on October 13, 1953.
The photos below show one of the units that now resides in my collection. It shipped to St. Louis on October 3, 1952.
I purchased this revolver from the son of the trooper who carried it on duty and was later promoted to Lieutenant. He purchased the revolver from the department when he retired, after the MSHP switched to the Model 66. The gun was delivered to him in a Model 66 box, which I now have. It makes sense that the department would use a current box to dispose of the older revolvers, since they probably did not still retain boxes from 1952.
Shawn McCarver and Russ Lindenlaub are the experts on these Missouri Combat Masterpieces, and perhaps they will chime in with further information.
What else did they carry?
Prior to the 1952 purchase, the standard sidearm for the MSHP was the .38/44 Heavy Duty with a 5" barrel. Desire to continue with that barrel length seems to have been the impetus for the special order to S&W for a 5" Combat Masterpiece.