Trident review: At-a-glance

The government has published a review, instigated by the Lib Dems, on "alternatives" to the Trident nuclear weapons system.

The UK's existing four ballistic missile submarines have to be renewed from the late 2020s and a final decision is due in 2016.

Here is a summary of the main points.

NUCLEAR DOCTRINE

  • Nuclear weapons will remain a "political tool of last resort" and be considered only "in the most extreme circumstances"

  • Their rationale is to deter extreme threats to the UK or to prevent an escalation that may risk "national survival"

  • The credibility of any weapons system is "crucial" but it must also be safe and secure and affordable

  • UK not able to conduct live tests of new warheads as signatory to Nuclear Test Ban Treaty

DELIVERY MECHANISMS

  • Modifying civilian aircraft to carry nuclear missiles "very high risk"

  • Stealth bomber expensive and would need support aircraft

  • Low orbit vehicles "too risky" for conversion to nuclear platforms

  • Mobile land-based missile launchers hard to protect and "operationally risky"

  • Missiles based at fixed silo locations "more vulnerable" to pre-emptive attack

  • Reconfiguring ballistic missile submarines to carry cruise missiles "discounted on cost grounds"

  • New "dual use" submarines could be built but fleet size would have to be expanded

MISSILES

  • Subsonic cruise missile potentially deliverable by 2035 despite technical challenges

  • Supersonic cruise missiles "vulnerable" as may have to be located too close to adversary

  • Hypersonic cruise missiles involve "extreme technical challenge" and multiplicity of platforms

  • Hyper glide vehicles too much of a "technical challenge"

  • Shorter range of cruise missiles could lead to "significant constraints" on UK options

  • Ballistic missiles could potentially target any country due to long range

WARHEADS

  • Cruise missile warhead twice as expensive as ballistic one - at up to £10bn

  • Length of time needed to develop cruise warhead and delivery system means two new ballistic submarines would have to be built in the interim to prevent a capability gap

POSTURES

  • Report distinguishes between high, medium and low readiness

  • Credibility based on readiness, reach, survivability and resolve

  • Only a fleet of four ballistic missile submarines and missiles housed in silos could provide 30-year continuous deterrent

  • For other platforms it would be "prohibitively expensive"

SUBMARINES

  • Cruise missile submarines more "vulnerable" to attack while on operations

  • Only a sophisticated adversary can "locate, track and engage" ballistic nuclear submarines

  • Three boats would not be sufficient to maintain continuous patrols and could lead to "multiple unplanned breaks"

  • Less regular patrols could be maintained with three or two boats based on Royal Navy priorities

INTERNATIONAL OBLIGATIONS

  • Any change may have wider implications for UK strategic interests

  • Reduced capability may increase reliance on allies for nuclear security

  • Cruise missile based system would be seen as "less capable" than a ballistic system

  • Increasing readiness from a non-continuous posture might lead to "misunderstanding"

  • Perceptions of the UK's commitment to multilateral nuclear disarmament may be increased

  • Any new system would have to comply with treaty obligations

COSTS

  • The reliability of estimates varies widely due to the long time period involved

  • Cruise missile platforms generally cheaper than ballistic ones

  • But added expenditure on missiles and warheads mean keeping ballistic submarines more cost-effective

  • Building three rather than four new Trident submarines would save money but only between 2025 and 2035

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