Britain’s Royal Navy said Wednesday that three of its members died in a helicopter crash earlier in southwest England during a training exercise.

According to a AP report, the helicopter went down in a field in the county of Devon in England just before 4 a.m.

The navy’s head General Gwyn Jenkins, said in a statement that he was “deeply saddened to share the news that three crewmembers onboard a Royal Navy Merlin Mk4 helicopter have died after it crashed in the early hours of this morning near Sourton, Devon.”

He said an investigation is under way and further updates will be provided in due course. It wasn’t immediately clear what caused the incident.

Merlin helicopters, such as the Merlin Mk4 involved in the incident, usually have a crew of four and can carry up to 24 troops. The Merlin helicopter is primarily used for anti-submarine warfare and is used for search and rescue, cargo transfers and maritime patrol, according to the Royal Navy’s website.

The Ministry of Defence said the families of the service personnel killed have been informed.