This was a US semi-clandestine air operation in the northern part of neutral Sweden (1943/1945).
The celebrated polar aviation pioneer Bernd Balchen, who had dual Norwegian and US nationality, was serving with the US Army Air Forces in mid-1943 when he was posted to Europe to run a special operation based at LuleŚ-Kallax air base in northern Sweden. This operation was conceived as a means of harassing German aircraft over Finland and occupied Norway, and also included a force of 10 Douglas Douglas C-47 transport aircraft. These latter were used to operate a route between Sweden and the UK, and this route was used many diplomats and others to reach the UK.
From March to December 1944 Balchen had available six Consolidated C-87 Liberator Liner transports (adapted B-24 bombers) flown by Office of Strategic Services crews, and in the 'Sonnie'' sub-operation that also operated to and from Bromma airport outside Stockholm, these were used to evacuate at least 2,000 Norwegians, 900 US internees and 150 other internees out of Sweden. The aircraft were also used to move police troops, who were Norwegian refugees trained in Sweden, from Sweden to Finnmark.
The undertaking also carried strategic freight: between July and October 1944 the aircraft delivered 64 tons of operational supplies, including ammunition, from Leuchars in Scotland to the resistance forces in German-occupied Norway. Other necessities, such as bales of hay and fodder for livestock, were also flown into areas of northern Sweden and Norway, and on one occasion a mobile hospital, complete with a doctor and nurse, was delivered by parachute.
Between November 1944 and April 1945, Balchen also transported 200 tons of Arctic equipment and operational supplies from the UK to Sweden to allow the establishment of a secret overland transport capability from Sweden to Norway. During the winter of 1944/45, the aircraft delivered communications equipment into northern Norway to improve the capabilities of Allied intelligence-gathering operations.