Also the show was shot on site in Cheyenne Mountain at the NORAD facility. A few floors up I /believe/, in a large portion that was not used anymore. The gate room was in a decommission missile silo as well. So in all likelihood the control room and blast shield were original to the complex, and not an installed set item after the fact. A lot of the soldiers you saw in the show were real ones which were stationed at the base there, so while they were extras, they weren't technically actors :D

I'm really surprised you didn't mention that important factoid!