The "Mole Hole" was the alert facility, where air crews lived next to their bombers for up to a week at a time. The building is located adjoining the "Christmas Tree", the alert apron where the bombers were stationed. Tunnels and tubes provided speedy egress from the building and access to the aircraft.
http://www.airforcebase.net/trips/maine/Loring_AFB_ME_20040503_02.JPG