Trident review: At-a-glance

  • Published

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 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


  • 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


  • 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


  • 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


  • 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"


  • 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


  • 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


  • 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