These aircraft were also used for reconnaissance missions in co-operation with "The British Commander-in-Chief's Mission to the Soviet Forces of Occupation in Germany", commonly known as "BRIXMIS". Known from 1956 as Operation Schooner and then Operation Nylon, they were authorised, at the highest level, on an irregular basis to carry out covert photographic reconnaissance flights. All flights had to be notified to the Berlin Air Safety Center (BASC), a quadripartite organisation responsible for authorising all flights in the three Air Corridors and the Berlin Control Zone (BCZ). All the Chipmunk Flight Notification Cards in the BASC were stamped by the Soviets "Safety of Flight Not Guaranteed" due to their interpretation of the 1946 Agreement as excluding flights outside West Berlin. Within the BCZ were many Soviet and East German military airfields and other installations.