Question to the Ministry of Defence:

To ask the Secretary of State for Defence, with reference to page 5 of the 2010 Strategic Defence and Security Review, what the saving was to the public purse of reducing the number of operational launch tubes on submarines to eight during the spending review period; and whether the £3.2 billion saving in the 10 years from 2010 was contingent on each Successor submarine having eight missile tubes armed with eight Trident D5 II missiles armed with 40 warheads.

The Successor submarine will be based on a 12-tube common missile compartment, but as stated in the 2010 Strategic Defence & Security Review (SDSR), it will be configured with only eight operational missiles, delivering a maximum of 40 nuclear warheads spread over these missiles. The submarines can sail with some tubes that are not configured with missiles. Such tubes would be configured with ballast cans to enable the submarine to dive.

There were no savings associated with reducing the number of operational launch tubes on Successor to eight, as it remained the case that the best value for money solution was the 12-tube missile compartment design.

The 2010 Trident Value for Money Review identified £3.2 billion of savings and deferrals over the next 10 years. These included the impact of reducing the cost of the submarine's missile compartment, resulting from an agreement with the US over the likely dimensions of the missile tubes (with consequent savings in predicted infrastructure changes) and the impact of a reduction in the overall UK warhead stockpile.