The hon. Gentleman knows, as I told him recently in reply to a Parliamentary Question, that we are going ahead with the purchase of nuclear machinery for our own Dreadnought submarine. As Polaris has not yet been fully proven or tried out in the United States, it is difficult to say what adjustments will be necessary to submarine hulls, but, certainly, some would be necessary, as otherwise our Dreadnought hull would not be able to take Polaris.