It was based on the real-life wartime exploits of Welsh engineer and munitions worker Melbourne Johns, who rescued machinery used to make guns for Spitfires and Hurricanes.

[4][5] It was an Ealing Studios film made in 1941 with the support of the War Office and the Free French Forces.

[6] In 1940, Welsh armaments factory foreman Fred Carrick goes to France on his own initiative to retrieve three large pieces of machinery for making cannon for Spitfires before the German army arrives.

During the race to the coast with the machines, he encounters a huge number of refugees fleeing the advancing Nazis and many more obstacles to hinder his progress.

Filmed during the war, location shooting for the scenes set in France was done in Cornwall, Kent, and Berkshire.