Well tough, because I found another one.
In the 1960's, the City of Detroit purchased a number of these carbines for their police department, one of only two big cities to do this. They issued them to their officers and the carbines rode the trunks of police cruisers and spent time in armory racks until 187 of carbines were finally sold for surplus to Zanders Sporting Goods for $75.00 each according to the stories. (This also apparently included some rare Irwin Pederson-produced guns...sigh.) They were then offered to the public and snapped up quickly. I missed out back then but I've been looking for one ever since and I finally came across one at a decent price...actually less than Zanders likely sold it for back then.
And how do I know it's one of those? Simple. DPD carbines have two distinctive markings that set them apart from the rest of the 6,000,000 or so carbines out there. The first is the DPD precinct and rack number stamped on the heel of the stock:
The rifle also bears a DPD inventory number on the side of the receiver, just barely visible at the wood line. Detroit assigned numbers sequentially to all of their firearms back then.
So this is one of those Detroit guns. Can't say 100% but she probably pulled riot duty in 1967 in addition to whatever else it was used for. Heck, maybe it even crossed paths with my Detroit PD-issued Smith and Wesson Model 10. The city sold these off back in the 1990's too, for $15.00 each to another wholesaler.
Haven't had a chance to shoot this critter yet, but that time's coming and a range report will follow. Meanwhile, looks like come the leftist revolution, I'm ready to head back to re-take Detroit in style.