That’s one big submarine:

• Her nuclear-powered engine will propel her through the water at more
  than 20 knots, yet the UK’s first stealth sub makes less noise than a
  baby dolphin, making her as good as undetectable by enemy ships.
• Astute’s
  sonar is so advanced that if she was lying in the English Channel she
  would be able to detect ships leaving New York harbour 3,000 nautical
  miles away (although the details of how she can do this are
  classified).
• The nuclear reactor will never need refuelling,
  and with an ability to make oxygen and drinking water out of sea water,
  the sub could stay underwater for its entire 25-year lifespan were it
  not for the needs of the crew.