Select Committee on Defence Written Evidence

Annex A


  21.  The years since the end of the Cold War have seen major technical changes to the Trident system. These have been partly driven by the US nuclear weapons laboratories, whose current annual budget of $6 billion massively exceeds the Cold War average of $3.8 billion.

  22.  These changes are often justified by the need to maintain the safety of the stockpile, and also to ensure that, if used, the warheads would be less indiscriminate (they would destroy military and political targets while killing fewer civilians). The latter point represents an attempt to mollify public hostility to any first strike against a non-nuclear state.

  23.  The changes made also mean that the upgraded Trident can better fit the USA's and UK's new post-Cold War objectives: specifically, it can hit targets across the globe and be rapidly retargeted at mobile missiles and other shifting targets. The key changes to the UK Trident system are as follows:

  24.   Extending the number of targets and rapid retargeting. The US Submarine-Launched Ballistic Missile Retargeting System (SRS) enables Trident submarines "to quickly, accurately and reliably retarget missiles to targets", and allows "timely and reliable processing of an increased number of targets". The system allows the USA rapidly to produce a nuclear attack plan using a small number of Trident warheads in a regional operation. The UK has purchased the fire control system, used to assign targets to the warheads on the submarines, at the core of SRS, and this has been installed in UK Trident submarines.

  25.   Single-warhead missiles. In 1993 Malcolm Rifkind argued that a hostile leader might gamble that the UK would never use Trident to secure its vital interests because of the public outrage that would follow a full-scale Trident attack. He therefore recommended the development of a "sub-strategic" Trident. This "sub-strategic" mission was first deployed on HMS Victorious in December 1995 and involved fitting some missiles with only one warhead.

  26.   Low-yield warheads. UK Trident may also have been made more "usable" by reducing the yield of the warheads. On 19 March 1998 the Secretary of State for Defence, Mr George Robertson, in reply to question by Ms. Roseanna Cunningham MP, stated that "The UK has some flexibility in the choice of yield for the warhead on its Trident missile." This flexibility may be intended to help fulfil the sub-strategic mission. A lower yield can be achieved by detonating only the atomic bomb part of the weapon, making it an atomic fission weapon rather than a hydrogen fusion weapon.

  27.  Further developments now under way in the US are also important. The close technical cooperation between the UK and the US mean that it is very likely that what is being developed in the US will later be adopted by the UK.

  28.  The US nuclear laboratories are continuing to develop the Trident system in ways that facilitate its use against targets across the globe. In 2005 the US Treasury allocated $1.7 billion for the development of the Trident D5 missile alone. Programmes under way include:

  29.   Reducing the yield of the W76 warhead. There appears to be a current programme to reduce the size of the nuclear explosion produced by the US W76 warhead. According to a July 2005 report in the Santa Fe New Mexican newspaper, the W76 is being modified so as to reduce its yield by 40% to 60 kilotons.

  30.   Improving the W76 warhead's ability to destroy hardened targets. If Trident's warhead could be made to explode close to the ground, then a low yield warhead could be used to destroy hardened targets such as missile silos. To achieve this the USA is seeking to give the W76 warhead a radar arming, firing and fusing mechanism similar to those fitted to the W88, which already has such a capability.

  31.   Improving the D5 missile's accuracy. If Trident was made more accurate, then a lower-yield warhead could be used to destroy a wide variety of targets. Recent years have seen a number of projects underway to give Trident "GPS-like accuracy" (about 10 million). The idea is to use GPS and/or inertial guidance to steer a manoeuvrable re-entry vehicle to its target. Manoeuvrability will be achieved either by adding controllable flaps or a moveable inside weight to the re-entry vehicle. Lockheed Martin has also sought to develop the idea that a super-accurate Trident could be used with a conventional warhead to destroy hardened targets.

  32.  These programmes are already becoming reality. The US Congress withdrew funding from the Navy's programme to improve the D5 missile's accuracy, but the Navy has been able to continue it using other funding, and in March 2005 the USS Tennessee carried out a test of a new re-entry vehicle with flaps and GPS guidance.

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