Closed for weapons testing?
Starting a separate thread for this. This occurred to me just now... did the Soviets know about the weapons testing which had the base closed off to visitors? It seems to me that they did, because Dovchenko kneeling to tie his shoelace so his men could fire over his back seemed rehearsed. So I think they knew the base would be closed to visitors with minimal personnel, making this the optimal time to break in.
Evidence against them knowing, though, or at least against them knowing what kind of test, and where, is the fact they seemed ignorant of Doom Town's purpose. And also there seemed to be little rush to leave initially, when you'd think there would've been if they'd known about a nearby nuclear blast. So I think they knew there was some kind of test, just not what, and didn't know until a little later at Doom Town.