Two respected Royal Navy officers have been sacked after they had an affair while serving on Britain's nuclear submarines – and endangered the nation's security by discussing top secret information by email.
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 that 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 his Yahoo email 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. She 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, dismissed from the military and handed a four-month suspended prison sentence.
Lt Brook, 30, had joined the Navy as an 18-year-old in 2011 but resigned in January this year. She was also formally dismissed and handed a suspended prison sentence of five months.
A judge castigated their behaviour, saying they had "compromised the security of the continuous at sea deterrent and both of you, as experienced submarines operatives, would have known that".
Lieutenant Commander Peter Barker, prosecuting, told the court martial: "Maintaining a nuclear deterrent has been achieved exclusively through a continuous at sea deterrent since April 1969.
"The effectiveness of this deterrent depends on the secrecy of the locations of our submarines."
He told Bulford Military Court in Wiltshire that at the time Lt Brook was a watch leader aboard HMS Victorious, while Lt Cdr Stone was a security officer on HMS Ambush.
Both submarines were based at HMS Clyde at Faslane on the Gare Loch, about 25 miles from Glasgow.
Lt Cdr Barker added: "They were, at this time, in a clandestine sexual relationship. Not least because Lt Cdr Stone was married with a young child.
"In July 2020, HMS Victorious was about to set sail for operational patrol. Lt Brook had remained in contact with Lt Cdr Stone by email, using her MODNet account to his Yahoo account.
"As this was not his MODNet account, this was an unrestricted means of communication.
"On the day of sailing, Lt Brook sent a number of emails to Lt Cdr Stone.
"This stream of emails... contained the location of the submarine for the next few days, the direction of travel, speed, diving depth and confirmation of the sailing time.
"The rest of the emails contain details of the ongoing relationship between the pair."
The court heard Lt Cdr Stone replied to these emails, but did not question why she had sent this information to an unrestricted email account.
In replying to these emails Lt Cdr Stone also re-sent the same information back to Lt Brook, as it was not deleted from the email chain.
Lt Cdr Barker added: "He replied to these emails. Within these replies included the emails Lt Brook had sent, therefore re-sending them by unrestricted means.
"He did not, at any stage, rebuke Lt Brook for sending these or delete the information from the email trail.
"He made no attempt to report the breach, knowing it was his duty as she was his subordinate, and knowing it would likely reveal their relationship."
The breaches were discovered by another officer before the submarine departed and they were reported, but Lt Brook was allowed to remain on the submarine for the five-month patrol, which was completed successfully.
Lt Cdr Barker added: "The information was particularly sensitive. It was judged to be a significant breach of operational security.
"It's not possible to know whether the information was intercepted and used by the enemy."
Jonathan Lynch, defending for Lt Brook, said: "She was somewhat of a trailblazer in the Royal Navy. She was the first female to volunteer for submarine service while at Dartmouth and was one of very few females accepted.
"She was the first female warfare officer and it was thought by some that she would be the first female captain of a submarine.
"The whole time she was in the Navy she felt a lot of pressure, the spotlight was on her because she was the first in her role."
The court heard Lt Brook struggled mentally with the demands of her role while she was going through 'very personal issues' and used Lt Cdr Stone as an 'emotional crutch', which was why she sent the email.
Lt Brook was also charged with nine counts of fraud, after she claimed for travel expenses from the base back to her family home in Sussex at £254 each time but did not actually make any of the journeys.
The court heard she resigned from the Navy in January this year and now runs a family car dealership.
David Richards, defending Lt Cdr Stone, said: "It's pretty obvious that there should be no discussion on an open source as to the movement of the nuclear deterrent.
"He was foolish and stupid and made a mistake without thinking to respond to her."
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Sentencing the pair, Judge Advocate Darren Reed said: "Such information is classified as secret or top secret.
"It gives away the initial patrol route and area of operations. Unsurprisingly, such information is classified as secret.
"Your culpability, Miss Brook, is higher because you deliberately disclosed this information, whereas Lt Cdr Stone was reckless in replying to your email.
"Such information, which concerns a submarine charged with carrying this country's continuous nuclear deterrent, will be of particular use to an adversary.
"The continuous at sea deterrent is the cornerstone of this country's assured and effective response to aggression.
"If an adversary knew where that submarine was that would weaken the nation's defences.
"You have potentially compromised the security of the continuous at sea deterrent and both of you, as experienced submarines operatives, would have known that."
Addressing Lt Cdr Stone directly, he added: "You were an experienced submarine officer. Your negligence had the potential to put the continuous at sea deterrent at risk."
Lt Cdr Stone, now of HMS Nelson shore base in Portsmouth, Hampshire, pleaded guilty to a charge of disclosing information useful to an enemy and a charge of negligence of duty. He was handed a four-month prison sentence, suspended for 12 months.
Lt Brook pleaded guilty to one charge of disclosing information useful to an enemy and nine counts of fraud. She was handed a five-month prison sentence, suspended for 12 months, and ordered to pay £2,286 compensation.
Both were dismissed from the military and ordered to carry out 60 hours of unpaid work.