633 squadron

When Norwegian resistance leader Lieutenant Erik Bergman (Chakiris) reports the location of a German V-2 rocket fuel plant, the Royal Air Force's 633 Squadron, under the command of Wing Commander Roy Grant (Cliff Robertson), is assigned the mission to destroy it.

The plant, however, is in a seemingly-impregnable location beneath an overhanging cliff at the end of a long, narrow fjord lined with anti-aircraft guns. The only way to destroy the plant is by collapsing the cliff on top of it, a job that only the 633 Squadron's light de Havilland Mosquitos are deemed capable of. The squadron trains for its mission in Scotland, where there are narrow valleys similar to the fjord.

The Norwegian resistance is supposed to destroy the anti-aircraft defences guarding the facility, but the attackers are all captured or shot, and the squadron is forced to attack with the defenses still intact. The factory is destroyed, partly due to Grant's plane circling to draw anti-aircraft fire away from the other aircraft making bombing runs. Most of the aircraft are destroyed, including Grant's. He is badly wounded in the crash, and is rescued by the Norwegians.

The film features real de Havilland Mosquitos, an aircraft nicknamed the "Wooden Wonder" because of its primary construction material. Although the Royal Air Force (RAF) had recently retired the type, a number of civilian operators had leased mostly former converted bomber examples (TT Mk 35) to the RAF for target-towing. Scouring RAF bases at Exeter, South Devon, Henlow, Shawbury and the Central Flying School at Little Risslington provided not only authentic aircraft but also vehicles and equipment that were representative of the wartime conditions.