Winston Churchill wanted to ban this film because he considered that it would demoralize audiences.
First film of Victor Beaumont.
The War Office asked Ealing to make a feature length training film for them on the subject of security, but provided minimal funds. Ealing more than doubled the budget from their own resources, to produce a film whose appeal transcended its military function. The very large profits from commercial distribution went first to repay this outlay, then to the War Office rather than Ealing.