Underground in a Titan II missile silo

Text and pics: Julian Edgar

Inside a massive underground complex designed to withstand nuclear attack and launch a devastating retaliatory strike

The whole doctrine of the Cold War's Mutually Assured Destruction required the ability to strike back after sustaining a nuclear attack. To do that, you needed retaliatory mechanisms that could withstand a targeted nuclear assault – and still function. The Titan II network of missile silos provided part of that assurance. Associated with air force bases in Arkansas, Kansas and Arizona, USA, the missiles were sited in underground firing complexes, located far enough apart that a direct nuclear attack on one silo was survivable by the others. There were 54 Titan II missiles, with 18 in each state.

Enormous underground complexes

The missile complexes were enormous. Each firing complex consisted of three underground parts – a silo that housed the vertically-standing missile completely underground, a control room, and a central blast lock and access portal containing lifts (elevators), decontamination showers and crew rest areas. Underground corridors, called cableways, connected the different parts.

It looks toy-like but the Titan II missile pictured in its underground silo at right is 31m (103ft) tall. There were 54 of these enormous underground facilities built in the US, each housing one missile. (Courtesy Titan Missile Museum.)

Construction of each site started with scooping out a ‘bathtub’, some 120m (440ft) long, 60m (200ft) wide and 12m (40ft) deep. The silo, control centre, blast lock and access portal were all contained in this excavation. The silo was excavated at one end of the bathtub, going down a further 33m (110ft) for a finished depth of about 46m (150ft). This excavation was made by a bulldozer at the base of the silo working in conjunction with a lift-bucket – a process known as ‘scrape and lift’.

The silo wall was 1.2m (4ft) thick for much of its depth, with the top 9m (30ft) increased in thickness to 2.5m (8ft). At the base of the silo, a huge wedge-shaped concrete blast deflector was constructed. Two large exhaust vents carried exhaust gas from the missile’s engine to the surface. The launch duct was lined with special sound-absorbing modules. These, and a water spray system, helped protect the missile from damage caused by high-intensity sound and vibration. The missile sat on a ring-like thrust mount, supported on four enormous springs. These allowed the missile to withstand the shock wave of nuclear attack. 

760 tonne door

A large #-shaped reinforced concrete beam sat on top of the silo, helping to support the silo door. The door, weighing 760t, had a top surface 75mm (3in) thick. It was moved by hydraulic jacks, and could be fully opened in about 20 seconds. Much of the complex’s construction was in steel-reinforced concrete, with more than 6400 cubic metres (8400 cubic yards) used at each site. More than 2200t of steel rebar was employed, with much of it an incredible 60mm (2.25in) thick.

The Titan II in its silo at the Titan Missile Museum, Arizona. The rectangular cut-out in the re-entry vehicle is to demonstrate to nuclear weapons inspectors that this is a deactivated missile.

Titan II was the largest and most powerful Intercontinental Ballistic Missile ever built by the US. The missile had a huge 9-megaton nuclear warhead (i.e. 9,000 kilotons, or 600 times the size of the Hiroshima bomb) that could be delivered to targets more than 10,000km (6,000mi) away in about 35 minutes. Each missile was capable of devastating an area of about 2300 square kilometres (900 square miles). The United States’ nuclear doctrine planned on using the Titan IIs as a deterrent that targeted large Soviet military bases and civilian population centres. The missile’s top speed was 25,700km/h (16,000mph) – more than 20 times the speed of sound.

Launchable within a minute

Unlike earlier US missiles, the Titan II did not use liquid oxygen. Liquid oxygen boils away rapidly at normal temperatures, meaning that it cannot be stored in the missile and instead must be loaded aboard the missile just before launch. Loading liquid oxygen took precious minutes that delayed retaliation and made the missiles vulnerable to attack. Instead of liquid oxygen, Titan II used two chemicals that were stable at temperatures of around 15.5°C (60°F). This allowed Titan II to be stored in its air-conditioned silo, fully-loaded at all times and ready to launch in less than a minute. In addition, Titan II was the first US missile that could be launched directly from its silo, further reducing its vulnerability to attack.

A Titan Missile Museum guide seated in front of one of the massive set of nested springs that support the underground control centre. These springs allowed the complex to withstand the earthquake-like vibrations of nearby nuclear attack. The tour is excellent.

The control room from which Armageddon could be launched. Each Titan II missile had a huge 9-megaton nuclear warhead (i.e. 9,000 kilotons, or 600 times the size of the Hiroshima bomb) that could be delivered to targets more than 10,000km (6,000mi) away in about 35 minutes.

Titan II was 31m (103ft) tall and 3m (10ft) in diameter. The re-entry vehicle, containing the atomic weapon, sat on top of the missile (it is often referred to as the nose cone). A two-stage rocket, Titan II was fuelled with a 50-50 blend of hydrazine and unsymmetrical dimethyl hydrazine, having the brand name of Aerozine 50. The oxidiser was nitrogen tetroxide. The two dangerous and toxic chemicals had to be kept separate at all times until launch. Inside the thrust chambers, the fuel and oxidiser ignited spontaneously in a process called hypergolic action – no spark or external ignition source was required.

The Stage 1 engine developed 20,000kg (430,000lb) of thrust and burned until it ran out of propellant after about 2.5 minutes. It was then jettisoned as Stage 2 ignited. The Stage 1 engine consumed about 96,000l (25,000g) of propellant (640l – 170g per second) and boosted the missile to an altitude of about 80km (50mi). Stage II burned for about 3 minutes and propelled the missile to an altitude of about 300km (200mi). It was then shut down at the appropriate time by the on-board guidance system. When the Stage II engine shut down, two small solid-fuel vernier motors fired to fine-tune the speed and direction of the missile. Stage II then separated from the missile and the re-entry vehicle, carrying the nuclear weapon, continued towards the target in a pre-planned ballistic trajectory. The weapon was the only part of the missile to reach the target.

Titan II entered active service with the US Air Force in 1963. Following decommissioning in the mid-1980s, the remaining missiles were converted into space-launch vehicles for satellites and were used in that role until the final Titan II was launched in 2003.

The Titan Missile Museum in Arizona comprises a complete launch complex. Excellent quality guided tours are available to take participants through most of the underground facilities. The missile museum is one of the most extraordinary places to visit in the world.  

Part of the skin of a Titan II missile. It is made from 2014-T6 aluminium, an alloy of aluminium and copper. (Author’s collection)

This article is extracted from my book Discovering Engineering that Changed the World.