The first Atlas ICBMs were set up on launch pads at Vandenberg AFB and Cape Canaveral just like any rocket of the time. On a pad with a gantry tower. Vulnerable even to angry pelicans.
The nest step was a hole in the ground. Not a vertical silo yet, but a big underground garage with huge roll back overhead doors.
The doors would be opened the missile cranked up into the vertical, filled with fuel and sent on it's way. Took about 3 to 6 hours- just enough time between when the Russian bombers showed up on the radar screens and what we see here was turned into molten glass.
That's a nosecone shroud for a hydrogen bomb mounted at the 'top'. Maybe it's one of those 25 megaton MK-41's - we don't have a lot of these booster warhead configurations yet (in the early 1960's) so we'd better make every one of them count!
This 'semi-hardened' Atlas facility was nicknamed the 'coffin configuration' because the missile was lying down in a box.