This is an old-style war film without glamorous actors and spectacular special effects; all the characters look quite ordinary, even the often-suave Michael Rennie, and there's no great romance. Thank goodness; this film is all the better for it. Other comments suggest there's a lot of fact in the film, and I'm not sure how much was liberty was taken with the actual heroic efforts of the Polish Resistance. A quick Google suggests that the Poles did find a V2 (not V1) rocket that had been fired, but that it was a Danish naval officer who discovered an early test version of the V1 that had crash-landed on a small island between Germany and Sweden. The officer sent a photograph and sketch of the bomb to Britain. In the film an actual rocket is loaded on to a Dakota aircraft in a sequence that I found unconvincing.
A previous commentator reckons that Rod Steiger made a brief uncredited appearance as a German officer. By the time the film was released, Steiger had starred in several films, not least "Run of the Arrow"; established actors sometimes make uncredited cameo appearances for fun or as a favour, but I was surprised by the claim that Steiger did appear in this film; if it was he, his acting against type was extremely good! Christopher Lee gets a high billing, but makes only a brief appearance.
A previous commentator reckons that Rod Steiger made a brief uncredited appearance as a German officer. By the time the film was released, Steiger had starred in several films, not least "Run of the Arrow"; established actors sometimes make uncredited cameo appearances for fun or as a favour, but I was surprised by the claim that Steiger did appear in this film; if it was he, his acting against type was extremely good! Christopher Lee gets a high billing, but makes only a brief appearance.