Nuclear History: Minuteman I Missile Silo

Nuclear weapons are fascinating objects that dominate my interest. Perhaps growing up during the waning years of the Cold War when hysteria far outpaced fact after 50 years of threatened nuclear annihilation sparked my fascination. By the late 1980s nukes had become so commonplace, along with the threat of Mutually Assured Destruction, that people resigned themselves to living quietly in the shadow of these great weapons of war in a state of lingering, simmering fear and malaise rather than panic. Terrible weapons of unspeakable power, nukes should be the ultimate taboo yet because sanity prevailed and the great bulk of the world’s nuclear arsenal has remained unused, these weapons are ‘safe’ to fawn over like a rabid fanboy. My academic education contained a strong focus on international treaties related to nuclear nonproliferation, an outgrowth of my youth Cold War paranoia. As such I enjoy the technical and legal aspects of nuclear weapons as much as the visceral emotions they engage. There is also a feeling of seeing under the veil of military high-security and secrecy that dominated the Cold War. These weapons and installations were long kept hidden, away from the average person’s eyes. Now that geopolitics have changed and many nuclear weapons and sites are obsolete, it’s thrilling to survey these once off-limits spaces.

At any rate, when traveling I try to take in roadside attractions related to the nuclear age. In May 2015, the attraction was Ellsworth Air Force Base for the SD Air and Space Museum and the Minuteman Missile National Historic Monument. I’ll try to make this post educational as well as showing off some cool Cold War history.

SD Air and Space Museum
Hyper-color retouch to highlight the clouds and lighting. In 1980s nuclear apocalypse movies, inverted colors like this were commonly used as effects to denote the detonation or radiological aftereffects of nuclear weapons.
National Parks Service
Minuteman Missile National Historic Monument Museum and admin building near Wall, SD. Tours to the silos start here, but there’s only two tours per day, with 6-10 people maximum per tour.

The Minuteman Missile Museum site did not have as many displays as I would have liked, but fortunately the SD Air and Space Museum at Ellsworth AFB provided the missing pieces. I’ll be mixing displays and photos from the two to narrate the story of the Midwest Minuteman I missiles. Like the tour, let’s begin at the Minuteman Missile Museum.

SD Air and Space Museum
Area of missile farms controlled by the 44th Missile Wing, encompassing the 66th, 67th, and 68th Missile Squadrons. The silos are spread out around Ellsworth AFB, however most of these were deactivated during START and other nonproliferation and arms reduction treaties. The missile silos you can visit today are located in the green field labeled D-1.

Minuteman I Missile

The Minuteman I intercontinental ballistic missile was designed by the Boeing Corporation in the late 1950s. Known as the LGM-30A, the missile’s first test flight was in February of 1961. The missile’s diameter is 6′ at the widest, standing some 53′ 8″. Flying at more than 15,000 mile per hour, the missile could deliver a nuclear warhead to a range in excess of 6,000 miles. Pretty impressive considering the space program was still pre-Apollo.

The Minuteman program was initiated in the wave of strategic panic following the Soviet Union’s 1955 hydrogen bomb test and 1957 Sputnik satellite launch. At the time people realized that if the Soviets could launch a satellite, then they could launch a weapon. The US had been working hard on a rocket program at the time, however the powers that be wanted only successful flights and were not ready to showcase the technology in the 1950s. The Soviet launch of Sputnik was both a surprise, and a sneaky punch at American technology by claiming first man-made object in space. The surprise lead to an Air Force contract to develop a “three-stage, solid-fueled missile that was to be extremely reliable, quick to launch, have maximum simplicity and a high capability for survival, and be able to remain on alert in its silo 24 hours a day, 7 days a week for many years,” known as Weapon System 133-A in February 1958.

The Minuteman I had a CEP of 1.3 miles when first deployed, but improvements to the guidance system dropped CEP to 0.69 mile by 1965. CEP is circular error probable, a measure of missile accuracy. CEP is determined by a circle with a radius in which 50% of the rounds will fall, or rather, the single warhead will fall into this radius 50% of the time. Planning target allocation for nuclear weapons assigns the size and number of nukes pointed at one spot by the likelihood of hitting that spot accurately enough to inflict the intended damage to a target. The larger the CEP, the more missiles, or larger the size of detonation is needed to ensure target destruction. CEP helped to drive the Cold War “missile gap” of the 1960s-1970s as planners believed more missiles were needed to adequately hit all the potential Soviet sites. If a CEP was larger enough that three missiles were needed to hit one site, then every Soviet missile silo targeted required three US missiles in a maddening spiral of armament escalation.

SD Air and Space Museum
Minuteman I missile on display at Ellsworth AFB.
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The business end. Minuteman I carried a 1.2 megaton W56 thermonuclear warhead.
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Handy Air Force markings in case you were to see a missile in flight, and wonder who owned it.
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Nozzles of the rocket engines. Minuteman has a three-stage system of booster rockets. The primary (1st stage) engine is a Thiokol solid-fuel motor pushing some 210,000 pounds of thrust. Final speed is ~15,000 miles per hour up to a 700 mile ceiling and ~8,100 mile range.
SD Air and Space Museum
Nozzle Assy, Rocket. The Air and Space Museum at Ellsworth AFB has a few relics of the only Minuteman test flight.

Sudden Sanity: Nuclear Disarmament Treaties

The Minuteman missile system underwent several variations. The current missile is the Minuteman III, capable of carrying three nuclear warheads. As the Minuteman I system aged, the number of active silos was reduced to 450 of the upgraded Minuteman II systems.

Disarmament talks between the US and USSR began in 1982. Both President Reagan and Premier Gorbachev were morally opposed to nuclear weapons, however the Cold War was at the the height of technological race between the countries. The talks fell apart in 1983 following US deployment of intermediate range nuclear missile in Europe. The derailment was a severe blow to reducing the threat of MAD overall, ultimately resulting in the INF Treaty which banned all such weapon systems in 1987. Strategic nuclear reduction talks followed on this success, resulting in the Strategic Arms Reduction Treaty in 1991. START was a milestone arms reduction treaty:

START I established an aggregate limit of 1,600 delivery vehicles and 6,000 warheads for each party (a reduction from 10-12,000 warheads in 1991). Within that limit, the Treaty established three sub-limits: 4,900 warheads for ICBMs (land-based intercontinental ballistic missiles) and SLBMs (submarine-launched ballistic missiles), 154 heavy ICBMs (defined as having a launch weight greater than 106t or a throw-weight greater than 4,350kg), 1,540 warheads for these heavy ICBMs (Only the Soviet Union possessed this type of missile), and 1,100 warheads for mobile ICBMs (de facto applied only to the Soviet Union and Russia because the United States, shortly after the signing of START I, decided to forego deployment of such missiles). The Treaty also established a limit of 3,600 metric tons (t) for the throw-weight of ballistic missiles.

Destruction of the majority of Minuteman missile silos was initiated to comply with START. Only the Delta-01 facility was spared, to be converted into a historical monument. Still, 450 Minuteman III missiles remain in the nuclear ICBM force. This number is slated to be further reduced by 50 missiles to comply with New START, signed in 2010.

Minuteman Silos

By 1964 the size of the silo-based Minuteman fleet numbered 1,000 missiles. Squadrons were organized from five flights. Each flight installation consisted of ten silos connected to a central control facility. Two launch officers watched over ten launch facilities and flights (five flights per squadron) in fields of 300 or so installations. Hardened underground cables connected the launch facilities.

The silo housing the missile was 80 feet deep and 12 feet across. Thick blast doors able to withstand up to 700 psi overpressure protected the silo from attack. The Launch Control Capsule containing the watch officers was buried fifty feet deep and could withstand 1,000 psi overpressure. The Capsule contained specialized stabilizing materials to absorb the shock wave from a nearby nuclear detonation, allowing the crew to launch even after an enemy first-strike. The launch crew could trigger all missiles in a squadron if needed during wartime, not just their own.

SD Air and Space Museum
A model of the Minuteman I missile in the silo. I thought the added arrow pointing up to indicate direction of travel for the missile was pointless, yet cute all the same.
SD Air and Space Museum
Model of the Launch Control Capsule buried underneath the control facility.

Launch Control Facility Delta-09 (missile silo)

The Delta-09 facility is located a quarter mile from I-80, between Wall and Kadoka, SD. The silo sits in a barren field, now topped by a thick protective shield of high-impact glass. It is a self-tour site with information accessed by radio prompts.

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Diagram of the Minuteman I missile silo and access hatches.
Minuteman 1
Minuteman I missile in the silo at Delta-09
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Close up of the missile. The thick glass shield is highly reflective, making it very difficult to take good photos of the silo or missile itself. I was quite disappointed by this.
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Thick blast doors once topped the silo.
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Access hatches to the equipment room where a backup generator was stored to allow launch of the missile if local power was cut by sabotage or first-strike. The white pole is an antenna.
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Hardened UHF antenna. May have been used to communicate with satellites and aircraft.
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Access hatch for maintenance crews.
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I’m not sure what purpose this hatch served. I think it has something to do with the security system or communication cables with the central launch control facility. 

Launch Control Facility Delta-01 (central launch facility)

The central launch control facility for the museum’s silo is located ~3 miles east from the silo. This facility is a guided tour offered by Parks staff, however I arrived too late for a full tour. The site remains tightly locked and under video surveillance when tours are not being taken through. Luckily for me, the SD Air and Space Museum has exhibits of the equipment and officers’ stations that were used for training so I didn’t miss out on much at Delta-01.

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Diagram of the central launch facility where Air Force officers kept long vigils over the missiles.
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Main entrance to Delta-01.
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The large building contained the barracks for the watch staff, weight room and exercise equipment, rec room, and other non-task related things the airmen on watch might need.
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Restricted Area.
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Gas pump at the gate was used to keep staff cars and the security vehicles running. Behind the fence is an old-model satellite dish. 
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The armored vehicle is a Cadillac Gage Ranger/Peacekeeper. The military used these vehicles throughout the 1970s and 1980s as heavy support for installation guards. It’s an ugly, squat little beast that completely encapsulates the theme and feel of the 1970s-era post-Vietnam War military.
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Close up of the Peacekeeper.

Launch Crew Capsule

The SD Air and Space Museum at Ellsworth AFB has a nice exhibit set up of the training system for the Minuteman I missile. This is an exact replica of the equipment buried under the Delta-01 Launch Control Facility. I don’t know what all of the equipment was used for, but it’s amusing to look at. Everything is 1970s and hardened against electromagnetic pulse so it’s very clunky and primitive compared to similar technology with which we’re familiar.

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Deputy commander’s console. The padded “barber’s chair” is mounted on rails to slide between equipment banks. The watch officer would strap into the seat to prevent being thrown around should a missile impact nearby. The seat was designed to absorb shock and allow the crew to remain able to fire their missiles if the facility was not completely eliminated.
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Commander’s console. The panels are warning lights with various issues. Launch-related warnings are on top, site security alarms on the bottom. Note the two telephones. Imagine the isolation of being sealed underground with no way to personally verify events on the surface.
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Close up of the warning alarms and codebook.
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Flight status panel. Flights were sub-divisions of missile squadrons, with flights to one launch control facility. The launch commander could monitor the status of his missile facilities by turning the central knob to “tune in” to a particular site.
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Launch verification and initiation panels. Note the location for the operator’s key. It took two keys turned at the same time to initiate launch. The Commander’s key panel is out of reach of the Deputy Commander’s panel to ensure one person could not launch by themselves.
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This is the modem for the electronic communication connection. How cool is this? Data received printed out underneath the unit.
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Modem, printer, and computer monitor. How’s that for a keyboard?
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Launch enable control group. Operators entered the verification code here to enable the key-turn launching equipment. The verification code was supposed to prevent sabotage or accidental launch without the highest approval. 
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