Seven teenage boys were airlifted off Dartmoor after getting lost while practising for the annual Ten Tors challenge.
The boys, all 14 and from a school in Wiltshire, called police at about 16:30 BST on Sunday after becoming disorientated by low cloud.
They were eventually found near Great Kneeset in the north west of the national park.
The Ten Tors challenge has been running more than 50 years.
It is organised by the Army for teams of 14-20-year-olds and takes place every May.
A spokesman for Devon and Cornwall Police said: "The boys, who were overdue in meeting up with their teachers, realised that they needed assistance and sensibly stopped walking in the worsening conditions.
"The helicopter crew searched the moor in the area of Hangingstone Hill and located the boys safe and well near Great Kneeset.
"As the conditions were deteriorating fast the helicopter lifted the boys and their kit from the moor, making two flights to and from Okehampton military camp, where they were reunited with their teachers."