A Royal Marine trainee has collapsed and died on an exercise in Dartmoor, the Ministry of Defence has confirmed, as an inquest begins into the deaths of three Army reservists during an SAS training exercise.
The marine, who has not been named at the request of his family, was based at the Commando Training Centre at Lympstone, Devon, and was taking part in a 30-mile march when he died.
An MoD spokesman said the cause of death was unknown and is being investigated.
He added: "The thoughts and sympathies of the Naval Service are with the family and friends of this man."
The marine died on Thursday during the so-called "30-miler" march across upland Dartmoor, the last major test undertaken as part of the 32-week Commando course.
Trainees must navigate the route themselves and complete it within eight hours while carrying additional safety equipment.
In July 2013, army reservists Edward Maher, Craig Roberts and James Dunsby died after collapsing during an SAS training exercise in the Brecon Beacon in Wales. An inquest into their deaths starts today in Solihull, West Midlands.
A number of other soldiers taking part in the programme that day, when temperatures hit 29C (84F), also collapsed and needed medical attention.
The long-awaited hearing, which is expected to last four weeks, will examine the circumstances surrounding the deaths which all occurred while the men took part in a military exercise on Pen Y Fan.
Roberts, aged 24 and from Penrhyn Bay, Conwy, was pronounced dead on the mountainside, while Maher and Dunsby, both 31, were taken to hospital.
Maher died three hours later in Merthyr Tydfil's Prince Charles Hospital while Dunsby, from Bath, Somerset, was transferred to the Queen Elizabeth Hospital in Birmingham, where he died on July 30.
Louise Hunt, senior coroner for Birmingham and Solihull, is expected to hear from soldiers who were manning checkpoints on the day, as well as other military personnel responsible for managing the exercise.
The inquest had originally been due to take place at the end of last year but was delayed to allow the Crown Prosecution Service time to review its decision not to bring criminal charges of gross negligence manslaughter over the deaths.
The service has since confirmed its original decision not to prosecute was correct.
A separate investigation by the Health and Safety Executive (HSE) and police is continuing.
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In October 2013, the HSE issued a Crown Improvement Notice on the Ministry of Defence over how it was managing risks, following an initial inquiry into how the exercise was run.
The MoD "complied with the notice and took action before the next selection test exercise" in January 2014, according to the HSE.