The secret entity, known as Air Force Unit 66, used a small fleet of civilian airplanes for operations that included transporting NATO operatives out of the country or depositing infiltrators along the Finnish border with the Soviet Union, Swedish daily Svenska Dagbladet reported.

Documents accessed by the newspaper’s reporter Mikael Holmström, the author of a new book about Sweden’s secret NATO links, show that the clandestine air force unit was a well-organized group consisting of a team of commanders, pilots and ground staff.

The unit received protection from the Swedish Security Service (Säkerhetspolisen – Säpo), and operatives were paid in cash in order to avoid a paper trail. The tax authorities received their due share in advance.

The head of the formation, using the code name Jan Danielsson, confirmed the existence of Unit 66.

“We carried out flights, exercises, and reconnaissance both in Sweden and in our neighbouring countries,” he told the author of the ‘The Secret Alliance’.

The unit used four-seater Cessna 182 and six-seater Cessna 206 planes, Svenska Dagbladet reported. As many of its operation were performed under the cover of darkness, the pilots were trained to land in difficult terrain with only flashlights to guide them.

Funding for the unit ran out in 1998 and the last planned operation was cancelled that year. The unit then ceased to operate, Holmström found.