 In 2000 a leak in the PWR1 reactor primary cooling circuit was discovered on "Tireless", forcing her to proceed to Gibraltar on diesel power.The fault was found to be due to thermal fatigue cracks, requiring the other "Trafalgar"-class boats, and some of the remaining "Swiftsure"-class boats, to be urgently inspected and if necessary modified.In 2013 the Defence Nuclear Safety Regulator reported that the reactor systems were suffering increasing technical problems due to ageing, requiring effective management.