After the Tehran Conference, the Partisans received official recognition as the legitimate national liberation force by the Allies, who subsequently set up the Balkan Air Force (under the influence and suggestion of Brigadier Fitzroy Maclean) with the aim to provide increased supplies and tactical air support for the Partisans. In February 1944, Mihailovic's Chetniks failed to fulfill British demands to demolish key bridges over the Morava and Ibar rivers, causing the British to withdraw their liaisons and halt supplying the Chetniks. Although British support for the Chetniks ceased, the Americans were less than enthusiastic about British abandonment of the anti-communist Chetniks. As support shifted towards the Partisans, Mihailović's Chetniks attempted to recommence Allied support for the Chetniks by displaying their eagerness to help the Allies. This eagerness to help was put into practice when the Office of Strategic Services (OSS) approached Mihailovic's Chetniks in mid 1944 to organise the airlift of downed US airmen. This operation known as the Halyard Mission resulted in the rescue of 417 US airmen that were previously kept safe by Mihailovic's Chetniks. Mihailović later received the Legion of Merit from US President Harry S. Truman for the rescue of Allied pilots.