Another Flying Saucer
It’s pretty obvious why the government would have wanted to keep this photograph secret until recently. We don’t know who’s the man in the picture, but it’s evident what’s the thing next to him: one of the flying saucers people used to report having seen during the 50s and 60s.
As said before, these were probably prototypes of some experimental aircraft devices. However, this one might not be American; it seems like it has been shot down, so it might have been a foreign reconnaissance aircraft.