Britain’s submarines are at sea for too long—or not at all

Britain has two sorts of subs. Four Vanguard-class boats, known as SSBNs, carry Trident nuclear weapons; one is at sea at all times. Six Trafalgar or Astute-class attack subs, or SSNs, carry conventional missiles, track Russian submarines and gather intelligence, among other duties. That is the largest force in Europe—France has one fewer SSN—but it is stretched thin.