It stars Stewart Granger, Raf Vallone, Mickey Rooney, Edd Byrnes, Henry Silva, Mia Massini, and William Campbell.

In 1943, British Intelligence in Cairo recruits Italian criminal mastermind Roberto Rocca, demolitions expert and Irish Republican Army member Terence Scanlon, forger Simon Fell, cold-blooded assassin John Durrell, and thief and impersonator Jean Saval for a dangerous mission.

After turning out a treatment based on the locale of Dubrovnik, Roger Corman teamed with screenwriter R. Wright Campbell who had a project, Dubious Patriots about a wartime mission involving convicts.

With a budget of $600,000, more than twice more than he had for his earlier independently-funded features, Corman was able to start production in between his Edgar Allan Poe adaptations, The Masque of the Red Death and The Tomb of Ligeia (1964).

[8][9] Principal photography under the working title of Dubious Patriots took place on location in Dubrovnik and other parts of Yugoslavia in the summer of 1963 for a typically short Corman shooting schedule of 36 days.

[Note 2] With the assistance of the Yugoslavian government, a large number of military personnel and equipment were offered, but an earthquake threatened to delay the production when troops were siphoned off to help in the relief effort.

[4][Note 3] Corman's problems extended to not only wrangling military extras, but also to dealing with the emotions of a star like Stewart Granger "stooping" to make a "B film" and worrying that his role was not as prominent as the others in the ensemble cast.