An investigation has been launched into behaviour on board a Royal Navy nuclear submarine.
Forces News understands that the Ministry of Defence (MoD) is conducting an inquiry into reports of an "inappropriate relationship" between crew members.
The captain of the vessel, who has not been named, has been relieved of his duties pending the outcome.
According to the BBC, the captain of HMS Vigilant is at the centre of the investigation and the allegations involve a female member of crew.
HMS Vigilant is one of the four Vanguard-class submarines that form the UK's strategic nuclear deterrent force.
The MoD refused to confirm the nature of the inquiry but said in a statement:
"We can confirm the Royal Navy is undertaking an investigation.
"While this is ongoing, it would be inappropriate to discuss further."
Discipline is one of the Royal Navy’s six core values, and they state in their guidelines that:
“The Naval Service must be a disciplined service if it is to be effective. We must, therefore, obey all lawful orders from our superiors.
"Self-discipline is fundamental; being able to discipline ourselves will earn us the respect and trust of others, and equip us to cope with difficult, individual decisions we will have to make during our service."
As might be expected, there are also strict Royal Navy rules about relationships on board vessels.
The ban on women serving on board submarines was lifted in 2011.
Men and women aboard Royal Navy ships are now given separate “mess decks” - the area where they sleep.
If a relationship between two individuals aboard is discovered then there is a risk of a court martial and even a dishonourable discharge.
In 2014, the first female commander of a frontline Royal Navy warship left her vessel due to claims that she had an affair with a shipmate.
She was “removed from command” from the Type 23 frigate and appointed to another position.
Commenting on the case in 2014, a spokesperson for the MoD said:
“Social misconduct has the potential to break down trust within military units which depend upon respect, loyalty and discipline to retain their close-knit structure and capability.”
The reasoning behind the strict rules on relationships is that there is a risk of relationships inhibiting the effectiveness of Royal Navy operations.
The rules are even stricter in the US military, where adultery is listed as a crime under the Unified Code of Military Justice, with punishments including not only dishonourable discharge but jail time.