Between 1943 and the end of the war, Mosquitos were used as transport aircraft on a regular route over the North Sea between Leuchars in Scotland and Stockholm, in neutral Sweden. Earlier, Lockheed Hudsons and Lodestars were used but these slower aircraft could only fly this route at night or in bad weather to avoid the risk of being shot down. During the long daylight hours of the Northern summer, the Mosquito was the safer alternative.

To ensure that the flights did not violate Sweden's neutrality, the aircraft carried civilian markings and were operated by crews who were nominally "civilian employees" of British Overseas Airways Corporation (BOAC). They carried small, high value cargoes such as precision ball bearings and machine-tool steel, as well as Diplomatic Bags. Important passengers were also carried in an improvised "cabin" in the bomb bay.