Trident missile

Trident missile

Infobox Weapon
name = Trident II

image_caption=The launch of a Trident II (D5) missile.
type = SLBM
vehicle_range = Greater than 4,000 nautical miles (4,600 statute miles, or 7,360 km)
filling = up to Eight W76/W88
yield = Up to 3.8 megatons
engine = three stage solid propellant
guidance = Inertial guidance system, with Star-Sighting
cep = 90 meters (if GPS guidance is used)
speed = 29,050 km/h (18,000 mph)
length = 44 ft (13.41 m)
diameter = 83 in (2.11 m)
weight = 58,500 kg (130,000 lb)
payload_capacity = 2,800 kg (6,170 lb)
manufacturer = Lockheed Martin Space Systems
unit_cost = $30.9 million [ [ The US Navy - Fact File ] ]
service = 1990–present
used_by = United States United Kingdom
:"This article contains technical information about the Trident ballistic missile. For a discussion of the British Trident weapons program, see UK Trident programme"

The Trident missile is a submarine-launched ballistic missile (SLBM) designed by Lockheed Martin Space Systems in the United States which is armed with nuclear warheads and is launched from SSBNs, nuclear-powered ballistic missile submarines. Trident missiles are carried by fourteen active US Navy "Ohio "class submarines and, with British warheads, four Royal Navy "Vanguard" class submarines.


Trident I (C4) was deployed in 1979 and phased out in the 1990s and early 2000s. Trident II (D5) was first deployed in 1990, and was planned to be in service for the thirty year life of the submarines, until 2027.

Trident missiles are provided to the United Kingdom under the terms of the 1963 Polaris Sales Agreement which was modified in 1982 for Trident. British Prime Minister Margaret Thatcher had written to President Carter on July 10 1980 to request that he approve supply of Trident I missiles. However in 1982 Thatcher wrote to President Reagan to request the United Kingdom be allowed to procure the Trident II (Trident D5) system, the procurement of which had been accelerated by the US Navy. This was agreed in March 1982. [ [ Reagan letter to Thatcher] ] Under the agreement, the United Kingdom made a 5% research and development contribution.

D5 life extension

A decision was taken in 2002 to extend the life of the submarines and the D5 missiles to the year 2042. This requires a D5 Life Extension (D5LE) Program, which is currently underway. The main aim is to replace obsolete components at minimal cost by leveraging commercial off the shelf (COTS) hardware; all the while maintaining the demonstrated performance of the existing Trident II missiles. In 2007, Lockheed Martin was awarded a total of $789.9 million in contracts to perform this work, which also includes upgrading the missiles' guidance and reentry systems. [Lockheed press release April 9, 2007] The British Prime Minister (Tony Blair at the time) was quoted as saying the issue would be fully debated in Parliament prior to a decision being taken. [BBC News [ Trident decision 'not yet taken'] ] And on December 4 2006, Tony Blair outlined plans in Parliament to build a new generation of submarines to carry existing Trident missiles, and join the D5LE project to refurbish them. [BBC News [ UK nuclear weapons plan unveiled] ]


The launch from the submarine occurs below the ocean surface. The missiles are ejected from their tubes by igniting an explosive charge in a separate container which is separated by two titanium alloy pinnacles activated by a triple alloy steam system. The energy from the blast is directed to a water tank, which is flash-vaporized to steam. The subsequent pressure spike is strong enough to eject the missile out of the tube and give it enough momentum to reach and clear the surface of the water. However, should this fail, there are several safety mechanisms that can either deactivate the missile before launch or proceed missile through an additional phase of launch. Inertial motion sensors are activated upon launch, and when the sensors detect downward acceleration after being blown out of the water, the first stage engine ignites, the aerospike extends, and the boost phase begins. The missile is pressurized with nitrogen to prevent the intrusion of water into any internal spaces, which could damage the missile or add weight which would destabilize the missile. When the third stage motor fires, within two minutes of launch, the missile is traveling faster than 20,000 ft/s (6,000 m/s), or 13,600 mph.

The missile attains a temporary low altitude orbit only a few minutes after launch. The Guidance System for the missile is an Inertial Guidance System with an additional Star-Sighting system, which is used to correct small positional errors that have accrued during the flight. GPS has been used on some test flights but is assumed not to be available for a real mission.

Once the Star-sighting system has been completed, the missile deploys the multiple independent reentry vehicles as their individual targets come within range. The lateral area coverage of the targets remains classified. The warheads enter the atmosphere at hypersonic speeds.

The Trident was built in two variants: the I (C4) UGM-96A and II (D5) UGM-133A. The C4 and D5 designations put the missiles within the "family" that started in 1960 with Polaris (A1, A2 and A3) and continued with the 1971 Poseidon (C3). Both Trident versions are three-stage, solid-propellant, inertially guided missiles whose range is increased by an aerospike, a telescoping outward extension that halves aerodynamic drag. In the post-boost phase, the Trident missile uses stellar sighting to update its position and reduce the drift error inherent in all inertial reference systems.

Trident I (C4) UGM-96A

The first eight Ohio-class subs were built with the Trident I missiles. Trident were also retrofitted onto 12 SSBNs of the James Madison and Benjamin Franklin classes, replacing Poseidon missiles.

* Purpose: strategic nuclear deterrence
* Contractor: Lockheed Martin Space Systems, Sunnyvale, California
* Propulsion: three stage solid propellant
* Length: 34 ft (10.2 m)
* Weight: 73,000 lb (33,142 kg)
* Diameter: 74 in (1.8 m)
* Range: 7400 km (4,600 statute miles)
* Guidance system: inertial, with Star-Sighting
* CEP: 1250 ft (380 m)
* Warhead: nuclear multiple independently targetable reentry vehicles (MIRV). Eight W76 (100 kt) warheads (Mark 4).
* Date deployed: 1979

Trident II (D5) UGM-133A

During the late 1970s, the Soviet Union developed a large number of heavy, increasingly accurate, MIRVed ICBMs (like the SS-18) that seriously threatened the survival of Minuteman III missiles in their silos. If the Soviet Union could have knocked out the majority of these missiles and the strategic bombers on ground, it would have left the United States with no counterforce capability for the second strike. The Poseidon and Trident I SLBMs were not accurate enough for counterforce strikes. If the Soviet first strike would have avoided hitting civil targets, the US might have been forced not to retaliate against Soviet cities, because of similar Soviet countercity capabilities. So the United States needed weapons which could survive a Soviet first-strike and neutralize the remaining Soviet strategic arsenal, in order to avoid the nuclear blackmail.

The second variant of the Trident is more sophisticated and can carry a heavier payload. It is accurate enough to be a first strike weapon. All three stages of the Trident II are made of graphite epoxy, making the missile much lighter. The Trident II was the original missile on the British Vanguard and "Ohio" SSBNs since USS "Tennessee" (SSBN-734). The D5 missile is currently carried by twelve Ohio class SSBNs. [Lockheed press release April 9, 2007] Lockheed has carried out 120 consecutive successful test launches of the D5 missile since 1989, according to a company press release.

* Purpose: strategic nuclear deterrence
* Contractor: Lockheed Martin Space Systems, Sunnyvale, California
* Unit Cost: $30.9 million
* Propulsion: three stage solid propellant
* Length: 44 ft (13.41 m)
* Weight: 130,000 lb (58,500 kg)
* Diameter: 83 in (2.11 m)
* Range: 9000 miles (11300 km)
* Maximum speed: 18,000 mph (29,030 km/h)
* Guidance system: inertial, with Star-Sighting
* CEP: 300-400 ft (90-120 m)
* Warhead (in USA usage only): nuclear MIRV. Up to eight W88 (475 kt) warheads (Mark 5) or eight W76 (100 kt) warheads (Mark 4). The Trident II can carry 12 MIRV warheads but START I reduces this to 8 and SORT reduces this yet further to 4 or 5.
* Date deployed: 1990

Conventional Trident

The Pentagon proposed the Conventional Trident Modification program in 2006 to diversify its strategic options, as part of a broader long-term strategy to develop worldwide rapid strike capabilities, dubbed "Prompt Global Strike".

The US $503 million program would have converted existing Trident II missiles (presumably two missiles per submarine) into conventional weapons, by fitting them with modified Mk4 reentry vehicles equipped with GPS for navigation update and a reentry guidance and control (trajectory correction) segment to perform 10 m class impact accuracy. No explosive is said to be used since the reentry vehicle's mass and hypersonic impact velocity provide sufficient mechanical energy and "effect". It offered the promise of accurate conventional strikes with little warning and flight time.

The primary drawback would have been establishing sufficient warning systems so that other nuclear countries would not mistake it for a nuclear launch. For that reason among others, this project raised a substantial debate before US Congress for the FY07 Defense budget, but also internationally. [*cite web | last = Wood, USA | first = Sgt. Sara | year = 2006 | url = | title = Conventional Missile System to Provide Diverse, Rapid Capabilities | publisher = U.S. Department of Defense | accessdate = 2006-04-10] Russian President Vladimir Putin, among others, warned that the project would increase the danger of accidental nuclear war. "The launch of such a missile could ... provoke a full-scale counterattack using strategic nuclear forces," Putin said in May 2006. [*cite web | last = Rosenberg | first = Eric | year = 2006
url = | title = Experts warn of an accidental atomic war | publisher = San Francisco Chronicle | accessdate = 2006-10-09

UK Renewal

On 14th March 2007, the government of the United Kingdom won Commons support for plans to renew the UK's nuclear submarine system. Between £15bn and £20bn will be spent on new submarines to carry the Trident missiles. The fleet will take an estimated 17 years to develop and build, and will last until 2050. More than 90 Labour members of the Commons voted against the proposed upgrade to the missile system, and the vote was only won with the support of the Opposition, although with the substantial support of 63% of MPs. [ [ Trident plan wins Commons support] . BBC News. March 15, 2007]


*Royal Navy
*United States Navy


ee also

* Nuclear weapons and the United States
* Nuclear weapons and the United Kingdom
* British Trident system
* British replacement of the Trident system

External links

* [ Video] of the Trident being launched.
* [ Trident I and II] , at
* [ Trident II D-5] , at Federation of American Scientists website
* [ Equipment, Features and capabilities of the Trident missile, including explanation of stellar sighting]
* [ Picture of the Trident missile compartment on a British Vanguard class submarine]
* [ Basic characteristics of Trident II D5]
* [ Current British Nuclear Weapons] at
* [ IEEE Xplore article]
* [ Ballistic Missile Submarines]
* [ Trident Ploughshares Campaign website]
* [ Time for a nuclear entente cordiale] , Bulletin of Atomic Scientists, September/October 2005
* [ UK's Parliamentary Defence Select Committee: Session 2001/02 Update on weapons programmes]
* [ US-UK Mutual Defence Agreement (MDA) 1958]
* [ HMS Vanguard Trident II test-launch - YouTube video]
* [ Lockheed press release April 9, 2007]
* [ Lockheed Press Release May 16, 2007] [ Forum for Vanguard Class Submariners]

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