Modifications, upgrades, and new warheads

As well as revealing the precarious state of nuclear safety at the Ministry of Defence, the recently released series of annual safety reports has also revealed some interesting insights into the UK's Trident nuclear warhead programme.

The reports refer to plans to  modify the current Trident nuclear warhead design by upgrading it with a new arming, fusing, and firing (AF&F) system.  The AF&F system is the 'trigger' which activates the explosive package of a warhead at the right height during its descent to ensure that maximum damage is caused to the target.  In a secretive programme which is rarely mentioned in public documents, the Ministry of Defence is upgrading its Mk4 Trident warheads by fitting them with the Mk4A AF&F system.

The upgrade will dramatically increase the military capability of the Trident system by allowing the power, impact, and radioactive fallout from the explosion to be changed, increasing its efficiency and giving the warhead the capability to destroy hardened targets.

Under the heading “Warhead Modification”, the 2006 safety report mentions that: “The Safety Justification Plan for the planned modification of the nuclear warhead (principally the Mk4A AF&F upgrade) is expected to be submitted in early 2007.  By 2008 “some delays are being experienced in the warhead modification project which are symptomatic of the proximity of the UK introduction programme to the completion of US development and production.  Similarly, not all safety evidence is yet available, and thus project decisions (for example, about [redacted]) are necessarily being based on assumptions”.

Leaving to one side any concerns that nuclear warhead safety decisions are being based on assumptions rather than evidence, it's interesting to see that this programme is described as an “upgrade”.  At the same time as the comments on the warhead modification programme were being circulated behind closed doors, the Secretary of State for Defence was saying publicly that the modification did not represent an upgrading of the system.

The Mk4A system is now in production in the USA, and the first of the new Mk4A warheads were delivered to the US Navy last year.  The upgraded version can be expected to enter service in the UK in the near future.  The modification programme is being managed by the Atomic Weapons Establishment (AWE), and  the Ministry of Defence has said that the costs associated with the Mk4A modification form part of the Nuclear Warhead Capability Sustainment Programme (NWCSP), suggesting that the NWCSP is much broader in scope than just the infrastructure investment and construction programme at AWE.

The annual safety report for 2009 includes a section entitled “Re-entry System (Options)” which states that: “Options are now being considered by SWPT [Strategic Weapons Project Team] and AWE for the maintenance of  nuclear warhead capability for current and future SSBNs.  When variability of ISD [in service date] for any successor warhead is factored in, a quite complex picture emerges in which continuing research and development of warhead technologies and features is a central theme”.  This seems to suggest that, even though the decision on a replacement warhead to the current design has now been deferred until around 2019 (the Strategic Defence and Security Review announced that a replacement warhead  is not required until at least the late 2030s), research into new warhead options and designs will be continuing at AWE regardless.