to access the missile silo, maintenance crews had to pass through
"formidable mechanical barriers" in a process that often took up to
an hour. First, a weather cover was opened, a combination entered, and the
vault door removed. This allowed for retraction of the locking shaft, and
operation of the hydraulic controls used to slowly raise the steel and concrete
primary door. The crew could then descend a few feet down the cylindrical shaft
and enter another combination into the secondary door (B-plug), and retract the
locking bolts. Following a preset, timed interval, the large steel B-plug would
slowly lower to the level of the upper equipment room. The crews could then
climb down into the equipment room surrounding the missile silo, lower their
equipment, and begin maintenance tasks. See, “Chapter 5, Maintenance Crew”
available from: http://www.nps.gov/mimi/historyculture/upload/The Missile Plains Section II Chapter 5.pdf.
In addition: Bruce Ecker’s spherical panoramic image of the Delta-9 LF at
Ellsworth AFB shows the personnel access doors open. (In 1991, Ellsworth AFB,
SD, was deactivated and Delta-1 LCF, and Delta-9 LF incorporated into the
National Park System. At Delta-9, a glass enclosure has been placed over the
top of the Minuteman missile in its silo for public viewing). Available from: http://nonplused.org/panos/minuteman/html/delta09.html.
Also, an image in the lower equipment room and the retracted B-plug is
available from: http://nonplused.org/panos/minuteman/html/delta09_silo4.html.