A ROYAL Navy attack submarine has been spotted leaving a Scottish port.

HMS Astute has returned to sea from Faslane according to the UK Defence Journal, following a lengthy maintenance and upgrade.

It marks an end to an over 100-day period where no British attack submarines were at sea.

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We previously reported on how all six of the UK’s Astute-class nuclear submarines were stuck in port – Faslane included – for repairs.

HMS Astute and its crew are likely undertaking a series of trials.

A Royal Navy spokesperson said: “To maintain operational security, we do not comment on the details of submarine operations.

The Royal Navy has delivered the UK’s continuous at sea deterrent without fail for the last 55 years.

“British waters are always fully protected with a range of assets including warships, patrol aircraft, and submarines.”