A Royal Marine recruit is in a life-threatening condition following a training exercise on a beach in Cornwall.
A group had been practising an assault from a landing craft on Tregantle beach near Plymouth when a man got into difficulty in the water.
South Western Ambulance Service said it was alerted at 22:00 GMT on Tuesday after “a person had gone underwater”.
The recruit, who had been in full kit, was airlifted to Derriford Hospital.
BBC defence correspondent Jonathan Beale said the recruit had to be resuscitated after he was recovered unconscious by the landing craft crew.
The recruits, who had full kit, backpacks and rifles, exited a landing craft close to the shore and reportedly struggled in the water, which was said to be up to their necks and cold.
They were in the last phase of their 32-week training.
The Royal Marines’ principal military training centre is situated near Lympstone in Devon.
A Royal Navy spokesperson said: “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.”
Up to 147 members of the armed forces have died while training or on exercise in the past 20 years. And of the 25 deaths in the Navy, 16 have been Royal Marines.
Former Royal Marines serviceman Saul Cuttell told the BBC the exercise is a “perfectly normal thing to do and it has a lot of validity to what a marine would have to do”.
He said the beach assault simulation is “tough” but “one of the things we [Marines] need to be able to do is replicate war time scenarios and they’re not easy scenarios, they’re not meant to be.”
While stressing he did not know the circumstances surrounding Tuesday’s incident, Mr Cuttell, who left the Marines in 2006, said the force has “made a lot of changes in recent years to ensure the safety of young men and ensure the training is more efficient”.
South Western Ambulance Service said it “was called on Tuesday at 22:01 about an incident at Tregantle beach, Cornwall”.
“The caller reported to us that a person had gone underwater. We sent land, air and other specialist paramedics to attend the incident,” a spokesman added.
“They treated a male patient at the scene and he was conveyed by air ambulance for further care.”