On December 2, 1960 the First National Bank of Boston opened a 7200 sq ft underground shelter in Pepperell, MA. The shelter was designed to protect the bank's records from nuclear attack. The facility had climate control, fire suppression, an office with bathroom and shower and a central alarm system. A 8 ton bank vault door served as the front door. Set in a residential neighborhood the property also included a house with 4 bedrooms and 3 and a half bathrooms all on 1.87 acres adjacent to a lovely 15 acre farm.
The vault is 14 feet underground with walls made of 1,500 cubic yards of concrete laced with 100 tons of reinforcing steel. It has a surplus atomic submarine escape hatch inscribed USS Nautilus at one end and a 16,000-pound safe door at the other. Engineers figured it could sustain a "medium" nuclear blast (5 to 10 megatons) as close as 5 miles away. In the sixties when the facility was built there wasn't much around to be targeted.
It is reported that packages arriving at the Pepperell post office in the early 1960s marked with an "X
Reportedly bank executives would relocate form Boston to the farmhouse when an international crisis loomed. Upon notice of an attack they would move into the bunker where cots and blankets were on hand for 50 people. Food rations were calculated to provide 842 calories daily for two weeks. The shelter had its own underground well, gasoline-driven generator, filtered air vents, and tanks for body waste.
There was a similar facility in CT. Check out "Horse Ridge Cellars" under "Business and Industry".