|Fig. 1: Trident II missile launch, followed by an eruption of water. (Source: Wikimedia Commons)|
The UGM-133 Trident II, also known as the Trident D-5, is a submarine-launched ballistic missile (SLBM) capable of carrying up to 12 nuclear warheads.  First built in the 1980s, it is a vital component of both the American and British nuclear weapons programmes. In 1983, Lockheed Martin were contracted to develop the missile, and, by 1987, they were launching it for the first time. Unfortunately, the initial launch was a failure, as the eruption of water that followed the missile rose higher than expected, causing the motor to ignite and bring the missile down (see Fig. 1). It was not until 1990 that the missile was eventually deemed fit for use - at which point it was quickly adopted by both the Americans and the British.  Today, Trident II missiles are carried by 14 US and 4 British submarines, with 24 missiles on each US vessel and 16 on each British.  In the coming years, as a result of global nuclear disarmament agreements, these numbers are likely to fall.
The Trident II was built as an improvement on the Trident I C-4, a SLBM first deployed in 1979.  It was designed to have greater accuracy (within a few feet) and range (7,000 miles) as well as being capable of carrying more and larger nuclear warheads. At 58.5 tonnes, it was also lighter than the C-4.  Perhaps most interestingly, the Trident II is not dependent on a Global Positioning System (GPS), meaning that even in the case where all GPS systems were down, it would still be able to hit its intended target. Instead, the Trident II uses a stellar sighting guidance system, since the missile, when fired, heads first into space (with a top speed of 13,400mph), before re-entering the earth's atmosphere to reach its target. The guidance system takes readings from the stars to figure out the missile's exact position. 
When combined with the nuclear warheads that are now equipped to the Trident D-5s, the total cost of the Trident missiles was, in the 1990s, 9.8 billion. 38% of this cost was incurred by the Americans, with the rest being paid for by the British. Today, an additional missile costs 16.8 million to build.  The real cost these days is maintenance, which is estimated to be over 2 billion per year.
© Misha Wilcockson. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Trident Missile Factfile," BBC News, 23 Sep 09.
 J. N Gibson, Nuclear Weapons of the United States (Schiffer Publishing Ltd, 2004).
 G. Spinardi, From Polaris to Trident: The Development of Fleet Ballistic Technology (Cambridge, 1994).