Britain maintains at least one SSBN (ballistic missile submarine) on patrol at all times. But this is running into problems because of a nearly 100 percent cost overrun at a new special maintenance dock for Britain's four SSBNs. The dock, and associated facilities for refueling and refurbishing the subs, was supposed to cost $760 million, but new safety standards, mismanagement and criminal fraud have pushed the cost to $1.5 billion. The situation is under investigation, and one SSBN is being refitted in improvised facilities.