YEP. Really. = I have SEEN one of the "auxiliary naval defense boats". - It was built on Solomon's Island, MD in the 1920s as a "buy boat" & originally belonged to a fishing buddy's grandfather.
(These days, it's used as a "live aboard".)
In 1942, the USN gave the owner a new "surplus" diesel engine for the buy-boat & that old engine is still "popping right along" the last time that I saw the boat.
The "buy boat" , at least in 1987, had the heavy MG mounts still installed fore & aft. = I asked "Thomas", "What ever happened to the machineguns?". He thought a minute, whether to answer or NOT, chuckled and then said, "Oh, I'd guess that they're still around, someplace.")
Btw, SOME machineguns (mostly BAR "Lightening" Models & TSMG) & shotguns were "loaned to the watermen" by the Maryland Department of Prisons.
I asked a Maryland Ranger (after a CSA memorial ceremony at Point Lookout Damnyankee DEATH Camp) some years ago if Maryland ever "recovered" the "loaned-out guns".
He thought for a minute & then said, "I think probably yes, except those 'reported to have been lost over the side' during the War."
(As I said earlier, the watermen of MD are NOT "pussycats"; instead they are full-grown wildcats.)