The same victims appear after both V-1 and V-2 attacks - the footage showing the rescue from a collapsed building has a shaggy headed (for 1944) man being helped from the wreckage (on the right side of the frame), shown as a distance shot through a hole in a wall, then first appearing, and finally stumbling out. Note there is one rescuer with a white helmet in all these scenes.
Early on in the film, a V-1 flying bomb - marked 'M23' on the tail fin - takes off, veers to the right and crashes. A few scenes later, Hanna Reitsch is seen in another flying bomb, which, in its first shot from distance on the ramp, is marked... 'M23'. This was obviously spotted, because in the next scene, a close up of the tail fin, it has now magically and clumsily been changed to 'M28'. Although it's much more likely very brief footage of the first rocket being fueled was used twice.
When Phil Bradley is interviewed for undercover work, he shows off his fluent German. Then, he is given a phony French identity and assigned to Belgium.
When Henshaw is shot, he falls into the crater face down at one end. However, a moment later he is shown lying face up at the other end of the crater.
Although piloted V-1s were built, they were launched from aircraft, not ramps. None were ever used in combat. Hanna Reitsch flew one to establish why other pilots crashed them on landing. She found that the problem was caused by the aircraft's exceptionally high stall speed.
Human piloted V-1s were never ground launched (using the ramp as in the movie) as the G-forces would have been too great. Human piloted V-1s were always air launched, from a carrying aircraft.
Robert Brown wears the uniform of a Royal Air Force Air Commodore however, his cap is mounted with the badge of a Junior/Senior Officer and not that of an Air Officer.
Although Gruppenführer (SS-Group Leader) Linz wears the correct rank insignia shoulder strap for the rank of Gruppenführer (equivalent to Wehrmacht Generalleutnant/Lieuteant General), his poorly made and not at all accurate collar badges rather resemble those of a Brigadeführer ( (equivalent to Wehrmacht Generalmajor/Major General)
One of the Lancasters is shown arriving at the release point with two engines stationary. While the aircraft could fly unloaded on two engines, both engines out on one wing would have been uncontrollable at the required power levels.
At the end of the film, the rocket being launched is shown as having four engines, whereas the V2 only had a single engine. However, this is supposed to be the long-range (and entirely fictitious) "New York" rocket.
When the agents are being briefed, they are shown a brief film clip. The blacks and greys in the projected image are much darker than the surrounding blank screen, as if the projector can project darkness as well as light.
When the German HQ is bombed the portrait of Hitler becomes detached from the wall before the bomb blast.
At around 1:31, multiple V-1 flying bombs are seen launching from their "ski-jump" ramps. The V-1 used a jettisonable launch dolly during their take-off runs. The first V-1 is seen jettisoning its launch dolly, but the other ones are not, revealing them as just models.
When the British Lancasters arrive at their target at the end of the film the skies, though dark, are nonetheless blue with white clouds. As it was about 11:30 pm, the skies should have been black. Further, with no city lights from below, the clouds should have also have been dark. Night clouds are only white, or bright, when reflecting light from the ground, from cities or towns. Without that light to reflect, clouds, at night, are dark, black.
At around 1:36, a fireman rescuing the casualties of a German attack is seen picking up a burning piece of timber with his bare hands.
Toward the end of the movie when a mail carrier is delivering the mail, you see her walking to the house and deliver the mail without any gloves on, when she starts walking away from the house she has gloves on.
When the first V-1 hits London, part of the front of the house begins to collapse before the fake explosion is triggered by the film crew.
Although the story takes circa 1943, Sophia Loren's hairstyle and makeup are strictly in the 1965 mode.
In the aerial shots of London as V-1s approach, 1960s era communications towers and power station cooling towers can be seen.
As the heroes cross into Germany from occupied Holland, the tri-colored German flag is on prominent display at the border post. This flag was ditched by the Nazis in 1933 and didn't come back into use until the late 1940s.
At several points through the movie, including a scene with Sophia Loren, characters are clearly smoking filtered cigarettes. Cigarettes manufactured with filters were not common until roughly a decade after the end of World War II. Although available, cigarettes with filters would be incredibly rare under the best of circumstances and likely completely unavailable, even on the Black Market, with war time shortages and rationing.
At least twice during the fire fight, George Peppard's machine gun is moving and the sound of a gun can be heard but there are no muzzle flashes as there at other times.
When launched, the flying bombs sound like propeller aircraft with internal combustion engines. They are supposed to be jet- or rocket-propelled.
When the first V-1 Flying Bombs are shown over London they are travelling North over Westminster, on that flight path they would have either hit The City of Westminster itself or the former Metropolitan Boroughs of Marylebone or Hampstead, now both part of the London Borough of Camden, where first V-1 actually hit was Grove Road in Bow, E3, around 6 miles East in what is now the London Borough of Tower Hamlets.
When Peppard and Courtney's characters are entering Germany on the Rhine River boat, their guide is speaking a broken English. However, as both are supposed to be fluent in German and possibly Dutch there is no need for English.