Three out of four British submarines equipped with nuclear missiles were at sea at the time, an extraordinary deployment not seen for more than five years.
At least one is believed to be carrying nuclear warheads, while the other two submarines are believed to be conducting routine sea trials.
A Navy official described the deployment as "unusual," though experts said it likely reflected an improvement in operational readiness rather than sending a strategic signal to Russia.
Source: The Times newspaper.
Telegram sources