Fallout or Bomb Shelters were both used to describe these underground structures.

Talking about the Nike Bases that were built to protect Bergstrom Air Force Base made me think back to the early 60s in Austin.

My dad was working for a construction company doing what I’ve spent my lifetime doing, installing underground utilities. The company transitioned into building “private underground bomb shelters” all over Austin.

The only one I remember ever seeing built was over in a neighborhood off of Airport Blvd., very near the old Austin Airport.
I wonder how many are still intact after all these decades.

The contractor was a man by the name of Lockwood. I hadn’t thought about that time for a long time now.

Many of the large buildings in every city that had basements were designated Fallout Shelters. Breckenridge Hospital is the one that I best remember.

https://orau.org/blog/museum/the-history-of-fallout-shelters-in-the-united-states.html