Hi Outdoorguy1950
Welcome to the Forum.
I was in the USAF around the same time period you were and carried the .38 Combat Masterpiece as well, but I wasn't stateside. Spent two years in SE Asia.
The Model 15s we had were -2 and -3. The -4 did not show up until 1977. But except for one small engineering change, the gun you just bought is the same as the one you carried in the service. Enjoy it.
Here's a pic of one of mine (a -2 from June, 1966).