The Trident II D5 ballistic missiles are carried by Britain's four Vanguard-class submarines, and they are able to deliver thermonuclear warheads from multiple independently-targetable re-entry vehicles (MIRVs). In July 1980 the U.K. requested, and the U.S. agreed to, the sale of Trident I missiles (less warheads), equipment, and services to the U.K. On 30 September 1980, the U.S. and U.K. letter agreements were formally implemented by an exchange of diplomatic notes that incorporated the TRIDENT sale into the POLARIS Sales Agreement.
In light of the U.S. DoD decision to develop and procure the TRIDENT II (D5) missile, the U.K., in order to maintain commonality with the U.S., requested in March 1982 that the U.S. sell them the TRIDENT II instead of the TRIDENT I. The U.S. agreed to this substitution in an exchange of letters between President Reagan and Prime Minister Thatcher.
The Director, SSP, is the U.S. project officer for this program, and the Chief Strategic Systems Executive (CSSE) is the British project officer. A small British staff from CSSE is assigned to SSP, and a U.S. liaison officer from SSP is assigned to duty in the British Ministry of Defense to ensure prompt and effective support to the U.K. programs. A Joint Steering Task Group, chaired by the respective Admirals in turn, meets alternately in London and Washington three times a year.
The Trident D5 missile is a three-stage solid-fuel rocket approximately 13 metres long, over two metres in diameter and weighing 60 tonnes. It has a range of over 6,000 kilometres. Each missile is technically capable of carrying up to twelve warheads and delivering them on to different targets with an accuracy that can be measured in metres. The advanced capabilities of the system enable it to carry out both the strategic and sub-strategic roles.
On 11 March 1982, agreement was reached between the U.K. and the U.S. to purchase the TRIDENT II missile system. The procurement of D5's replaced the U.K.'s original request of 10 July 1980 to procure C4's.
Although the Trident missiles are being bought from the United States, their warheads and the submarines that carry them are British designed and built. The warheads are designed by the Atomic Weapons Establishment at Aldermaston and assembled at Aldermaston and Burghfield.
The Vanguard Class submarines are larger than the Resolution Class mainly because of the need to accommodate the Trident D5 missile. The 16-tube missile compartment is based on the design of the 24-tube system used by the United States Navy's Ohio Class Trident submarines. Although each Vanguard Class submarine is capable of carrying 192 warheads, the boats will deploy with no more than 96, and possibly with significantly fewer.
The TRIDENT II (D5) Life Extension Program extends the service life of the TRIDENT II (D5) Strategic Weapons System to support the extended service life of the OHIO Class Submarine to 45 years. This program, the result of a Navy/OSD study, is designed to extend the production and sustain the effectiveness of the TRIDENT II Strategic Weapons System to 2042. The 2001 Nuclear Posture Review (NPR) supported full funding for D5 Life Extension and the Navy revalidated this low rate production continuity acquisition strategy in a report to Congress in 2002. The TRIDENT II (D5) Life Extension Program will be accomplished through upgrades to missile and guidance electronics to mitigate obsolescence, and through the continued production of critical missile components.
According to the Nuclear Information Service (NIS) an independent body which works to promote public awareness and foster debate on nuclear disarmament by 2016 Britain's Atomic Weapons Establishment (AWE) was working on a program to upgrade the current UK Trident warhead to the 'Mark 4A' modified warhead, which will have increased accuracy and destructive power and an extended lifetime. "Parliament has never been formally notified of the Mark 4A modification program and the costs and timetable for the program have never been disclosed. Nevertheless, the policy of successive UK governments has been to achieve a world without nuclear weapons, so it is incontrovertible that at some point in the future nuclear weapons production and maintenance at AWE must cease," the May 2016 NIS report said.
The Mark 4A warhead modification programme will allow Trident nuclear warheads to remain in service until the middle of this century, and plenty of money is being spent to pave the way for developing a new generation warhead which will remain in service for even longer, said Peter Burt, director of the Nuclear Information Service.
The number of warheads on board each submarine would be reduced from a maximum of 48 to a maximum of 40, the number of operational missiles on the Vanguard Class submarines would be reduced to no more than eight, and the number of operational warheads reduced from fewer than 160 to no more than 120.
On 22 January 2017 The Sunday Times revealed that the British government covered up a Trident II D5 missile test gone awry in June 2016, just weeks before a crucial parliamentary vote on the future of the weapons system. The Trident ballistic missile was set to be tested for the first time in four years. There had only been five firing tests by UK Vanguard-class submarines in the 21st century, the Sunday Times wrote, and the launches are usually big occasions for the Royal Navy, as the missiles cost 17 million pounds ($21 million) apiece.
In its report, the newspaper indicated that the unarmed, nuclear-capable Trident missile "experienced an alarming failure" following a test launch from HMS Vengeance, a British submarine off the coast of Florida. During the test, the unarmed missile "may have veered off in the wrong direction towards America" after being launched, before splashing down in the water according to the article. A senior naval source anonymously told the Times that "there was severe panic that this test launch was not successful," adding that "senior figures in military and government were keen that the information was not made public." However, Sky News quoted its Defence Correspondent Alistair Bunkall as saying that he had been told that the earlier report about the missile veering towards the United States is not true.
A government statement indicated there was a "routine unarmed Trident missile test launch from HMS Vengeance" in June. The Royal Navy launch was "part of an operation which is designed to certify the submarine and its crew," the statement said. The Vengeance submarine and its crew were "successfully tested and certified," it said. The statement said the government does not provide further details on submarine operations for "obvious" national security reasons.
Scottish National Party leader Nicola Sturgeon, who opposes having the Trident submarine fleet based in Scotland, said reports of a failure and cover-up are a "hugely serious issue." Labour Party leader Jeremy Corbyn, also a Trident opponent, called it "a pretty catastrophic error."
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