Children as young as 12 were marooned on mountains in treacherous conditions with inadequate supervision and clothing after a series of failures by expedition organisers, documents seen by the Observer reveal.

More than 70 children from Cleveland army cadet force, some taking part in the Duke of Edinburgh awards programme, were walking across Northern Ireland’s Mourne Mountains last August when the weather turned, leaving them isolated and exposed to the elements. Eight had to be stretchered off the mountain by the emergency services.

Internal army reports, released under the Freedom of Information Act, note that the incident “could easily have been more serious” and “the conditions for potential and serious failure had existed for some time”.They question the risk assessments carried out before outdoor adventure programmes and raise the need for adequate contingency planning.

One assessment notes that the trip’s exercise director had assumed that the Mourne Mountains were classified as “normal” when they are actually designated as “wild country”, making them unsuitable for the training of certain classes of cadet. It continues: “It is suspected that some of the leaders/supervisors were not sufficiently qualified or experienced to lead expeditions in the Mourne Mountains” and says that two of the cadet teams did not have a dedicated adult instructor.

Normally such trips would have an instructor to student ratio of 1:10. But one team leader was responsible for 19 cadets. The report notes: “On arrival (at the emergency rendezvous) there were only five adult instructors with the 64 cadets remaining on the mountain (a ratio of almost 1:13), which exceeded all of the recommended ratios.”

The youngsters – aged between 12 and 17 – were issued with waterproof clothing but all were “soaked through to the skin within 30 minutes”. Many had gone without breakfast on the morning of the rescue “due to [a] pressure to get moving” which “no doubt contributed to the resilience of cadets in adverse weather conditions”.

The expedition organisers used a weather app to ascertain the conditions, which was unsuitable for establishing the true conditions the cadets would encounter.

The day of the rescue experts said they believed a risk assessment must have been conducted.

Military veteran Doug Beattie told the Belfast Telegraph that “when you take young people to places like the Mourne Mountains, they do a very detailed risk assessment and make sure that they have very detailed plans in operation.”

But one report notes that the reconnaissance of the route had been conducted by a Duke of Edinburgh officer who had been given a risk assessment by an external adventure training provider which, he “believed, removed his planning responsibility, a serious error”.

It emerged that an earlier expedition had been scrapped because of a lack of qualified instructors, on the advice of an army training services adviser. But, the report notes, “the TSA was not shown the instruction for the Mournes expedition”.

It concludes: “What happened on the Mourne Mountains can best be described as a ‘near miss’. The (force) commandant has put into place manpower changes and assurance processes to prevent it happening again.”