Oh, I fully appreciate the possibility that the USNR stamp was, well, unofficial. Then again, I can't imagine why someone would do that.
On the other hand, I've visited Sampson Naval Training Station on Lake Seneca, and to say it was thrown together and then torn to pieces -- all in a matter of months -- is a huge understatement. In less than six months, the rural area went from having a population of about 100 farmers to having a population of 30,000 to 40,000 construction workers and sailors.
All sorts of ad hoc, seat of the pants stuff went on there -- for example, at least one of the infamous Japanese "mini-subs" was brought to Sampson for testing -- and some natives say the military still has strange and wonderful stuff stashed in large bunker areas that are still closed off to the public.
For more on Sampson, visit: