Three of Britain's four Vanguard-class nuclear submarines went to sea at the same time, The Times reported, citing a source who called such activity "extraordinary". The simultaneous presence of three such submarines on duty or in transit at once does not happen often. As a military expert explained to Sky News, at least one of the boats carries ballistic missiles with nuclear warheads on planned patrols, the second is preparing to enter combat service, and the third may undergo sea trials. Such a deployment could send a message to NATO allies and potential adversaries.