Committees on Arms ExportsLetter to the Chair of the Committees from Rt Hon William Hague MP, First Secretary of State and Secretary of State for Foreign and Commonwealth Affairs, Foreign and Commonwealth Office

Thank you for your letter of 30 January in which you posed questions relating to the “sub-strategic” capability of Trident.

The term “sub-strategic” as it pertains to nuclear weapons has been used in NATO since the 1980s to refer to intermediate and short-range nuclear weapons. Between 1966 and 1998 the UK fulfilled this role principally through the WE177 air-launched bomb. Other systems included nuclear weapons aboard Royal Navy surface ships. These have now all been withdrawn, (the last WE177 was decommissioned in March 1998), and the Trident-based weapons system is now the UK’s only nuclear weapons system.

Since the Trident system came into service, we have had some flexibility in the scale of any use of our nuclear deterrent. This flexibility stems from an ability to vary the number of missiles and warheads which might be used and the ability to employ a reduced yield from our nuclear warhead. We plan to retain this since baying a degree of flexibility in the potential scale of its use makes our “deterrent more credible against the range of nuclear threats we may face in the future.”

What has changed is the way in which we describe this capability and this is where we currently differ slightly from NATO terminology. Since 2007 the British Government has ceased to refer to a sub-strategic capability in relation to Trident. This is for the simple reason that we believe any use of our deterrent would be strategic in intent and in effect. Since the British Government no longer uses the phrase “sub-strategic” to describe this capability and there exists no internationally agreed definition of what comprises a sub-strategic nuclear capability, the British Government ascribes no specific range to the term “sub-strategic”.

As regards your final question, we do not consider that any of the capabilities of Trident represent a potential breache to the terms of the intermediate-range nuclear forces Treaty (INF).

20 February 2012