Two Royal Navy officers who had a 'clandestine affair' on a nuclear submarine are sacked for leaking top secret information in email

Portsmouth-based submariner Lieutenant Commander Nicholas Stone and Lieutenant Sophie Brook put the secrecy of the UK's Trident nuclear deterrent at risk by sharing classified submarine movements which could have been intercepted by an enemy, a court martial heard.

Their messages contained the departure time as well as the direction, speed and depth of travel of Vanguard-class submarine HMS Victorious all of which 'would have been useful to an enemy' and risked weakening the 'cornerstone' of the nation's nuclear deterrent.

The messages – to Lt Cdr Stone’s Yahoo account – were sent as part of a 'clandestine sexual relationship' between the pair despite Lt Cdr Stone being married with two children.

The court heard both were highly respected officers and Lt Brook was considered a Royal Navy 'trailblazer' as the first female warfare officer on a nuclear sub and had even been tipped to become the first female captain of a submarine.

Today their careers and reputations were in tatters, with 37-year-old Lt Cdr Stone, who has served in the Royal Navy since 2003 and was based at HMS Nelson, dismissed from the military and handed a suspended prison sentence of four months

Lt Brook, 30, had joined the navy as an 18-year-old in 2011 but resigned in January. She was also formally dismissed and handed a suspended prison sentence of five months.

A judge blasted them for their behaviour, which had 'compromised the security of the continuous at sea deterrent and both of you, as experienced submarine operatives, would have known that'.

Both submariners were based at HMS Clyde at Faslane, about 25 miles from Glasgow.

At the time, they were 'in a clandestine sexual relationship', Lt Cdr Peter Barker, prosecuting, said.

'Not least because Lt Cdr Stone was married with a young child,’ he added.

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In July of that year, HMS Victorious was about to set sail for operational patrol. The court martial heard that on the day of sailing, Brook sent a number of emails to Stone – using her secure MODNet account to send messages to his Yahoo account.

The breaches were discovered by another officer before the submarine departed but Brook was allowed to remain on board.

‘The information was particularly sensitive. It was judged to be a significant breach of operational security,’ said Lt Cdr Barker.

‘It's not possible to know whether the information was intercepted and used by the enemy.’

Jonathan Lynch, defending Brook, said she’d been 'somewhat of a trailblazer in the Royal Navy' but had 'felt a lot of pressure' being in the 'spotlight', and had used Stone as an 'emotional crutch'.

David Richards, defending Stone, said he’d been 'foolish and stupid and made a mistake without thinking to respond to her’.

Brook and Stone pleaded guilty to all charges. Sentencing them, Judge Advocate Darren Reed told Brook her culpability was higher 'because you deliberately disclosed this information'.

Stone had been 'reckless in replying to your email', he added. 'The continuous at-sea deterrent is the cornerstone of this country's assured and effective response to aggression.'

Both were dismissed from the military and ordered to carry out 60 hours of unpaid work.