Lt.-Col. John Cater, the commanding officer of the Greenwood Cadet Training Centre, said Wednesday the teen was taking a day off on Tuesday when he came out of his room around 1 p.m. and reported he felt sick.
"He did lose consciousness and was unresponsive," Cater said.
The boy was rushed to a hospital in Kentville, N.S., around 3 p.m. and later died.
In an email to parents at École Samuel-De-Champlain in Saint John, where the teen was a student, school officials said Wednesday they were all hit hard by the loss. The building will be open to the community on Thursday from 7 p.m. to 9 p.m. to provide an informal gathering place for those needing it, the email said.
The school said funeral details would be announced at a later date.
"We are working with the family to ensure they have all of the assistance we can provide for them and ensure their well-being," Cater said.
Cater would not disclose whether the teen had any medical conditions. He said that information would have been shared with medical staff when the camp started.
"On arrival, every cadet is screened by our medical staff and if they do have an allergy that requires an EpiPen, they are advised and counselled on the fact that they have to keep it with them at all times in order to access it when they need it," he said.
Cater said since the teenager died suddenly, the Canadian Forces National Investigation Service — the investigative arm of the military police — will look into the matter.
There's no word on the cause of the boy's death.
The base made grief counsellors available, Cater said.
"It is business as usual, but we did made it clear to all the cadets and all of the staff that the training is secondary and the needs of the cadets and the staff are paramount and they trump all other considerations," he said.
Instructors reminded cadets to carry personal medications, drink water and take rests.
About 1,000 cadets go through the summer program. They range from age 12 to 18.
A family spokesperson contacted CBC News on Wednesday afternoon and said the New Brunswick school board had earlier released the teenager's name without the family's permission.