The UK MOD has taken all twelve of its nuclear hunter-killer submarines off active duty because of fears that a fault in the reactor cooling system, first identified in HMS Tireless, a Trafalgar class boat, may be present in all of them. The twelve boats, five Swiftsure class and seven Trafalgar class, will now undergo lengthy tests to determine if the defect identified on the Tireless is present in any other.

The discovery is an embarrassment for the Royal Navy since it now has no conventional submarines to patrol its areas of responsibility. At the end of the Cold War, the MOD decided to scrap diesel submarines in favour of an all nuclear submarine fleet. The last class of four diesel boats, the Upholder class, has been sold to Canada.