Trident review: At-a-glance

16 July 2013

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