A Royal Marine is fighting for his life at Derriford Hospital in Plymouth after getting into difficulties while training on a beach in Cornwall.
The man, who is yet to be named, was pulled from the sea off Tregantle Beach near Plymouth on Tuesday 21 January.
It's thought he is a recruit and was in full kit at the time.
His next of kin have been informed.
A Royal Navy spokesperson said in a statement:
We are aware of an incident involving a member of the Royal Marines in Plymouth. The next of kin have been informed and we ask for privacy for the family. The incident is currently under investigation, therefore it would be inappropriate to comment further.
South Western Ambulance Service said it was alerted to an incident on Tregantle Beach at around 10pm on Tuesday evening.
A caller was told a person "had gone underwater". The service sent land, air and other specialist paramedics to the scene.
A spokesperson said: “They treated a male patient at the scene and he was conveyed by air ambulance for further care.”