Teams set off to tackle 'immensely tough' Ten Tors
BBCThousands of teenagers are starting the 63rd Ten Tors Challenge on Dartmoor.
The annual challenge, organised by the British Army's Headquarters South West, sees teams navigate routes across the northern half of Dartmoor in under two days.
It is usually attempted by about 2,400 teenagers in 400 teams of six, with routes ranging between 35 and 55 miles (56-88km).
Up to 400 young people with special needs were taking part in the Jubilee Challenge, a one-day event across four different routes.
Teams in the main expedition were due to set off from Okehampton Camp at 07:00 and must return by 17:00 on Sunday.
Participants must follow their allocated route, which specifies which staffed locations must be visited and in what order, but it is up to teams to identify and navigate their own ways between them.
The Army Headquarters South West said the challenge was "immensely tough".
"Those teenagers taking part will trek unaided... and will encounter some of the toughest terrain and highest peaks in southern England," it said.
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