When Barnes Wallis meets Summers and they decide to approach Bomber Command, outside the testing chamber is a Fiat 'Topolino' (the original version of the Fiat 500). This is very unlikely to have been imported to Britain before the War and certainly it would have been impossible during it, Italy being an enemy nation. Possibly it was chosen as an authentically 1930s style car that was readily obtainable in 1955.
After the first failure of the full size test bomb, Guy Gibson, Bob Hay and Barnes Wallis are saying goodbye to each other. Bob Hay's mouth moves but what he says to Barnes Wallis is not heard. (at around 25 mins)
When testing the use of spotlights to determine the aircraft height, a crew member is giving instructions to the pilot to carefully fly lower, but in the middle of the sequence the aircraft is seen to turn sharply to the left, which would mean the spotlights would no longer be pointing downwards and giving instructions at this point would be useless.
Guy Gibson was depicted as congenial, friendly and gregarious. However people he worked with, both air crews and ground staff considered him to be a loner, a strict disciplinarian and having little personality.
When Gibson meets with Wallis at the final drop test, he tells Wallis that they have been able to fly at 60 feet. Wallis is astonished, though of course very pleased. However that was one of the major requirements, in order to prevent the bomb casing bursting as it did when dropped from higher up. Surely Wallis would have been told in advance that "Mutt" was able to fly at 60 feet for the drop test - especially as Gibson told Wallis that they had been doing it for a week - otherwise there wouldn't have been any point in conducting the test.
Gibson and Whitworth are sent off to select pilots for the new squadron. Their first selection is Les Knight, we are shown a photo of the actor Vincent Ball but when we meet the character Les Knight he is actually played by Denys Graham.
American versions had "Trigger" dubbed for "Nigger" (the name of Gibson's dog, and one of the code words). The Morse code received in the Ops room was still "Nigger" though.
In US prints (see trivia entry), a Flying Fortress appears at least once in place of a Lancaster.
During training flights shown early in the film when crews knew nothing about the target or weapon, Lancasters are shown carrying the bouncing bomb that was used on the actual mission.
When Barnes Wallis starts to pull the blackout across it is clearly daytime outside. He stops and walks through the French windows and suddenly it's night time and dark.
Prior to the Raid, Henry Maudslay brushes his hair and puts the two brushes together by their bristles. After the Raid, from which Maudslay does not return, a shot of his room shows the two brushes side by side.
When the first dam is breached, during the fly over back over the reservoir, underwater jets can be seen in the miniature, driving the flow of water through the gap in the model dam.
The Castle above the Eder-Dam is shown on the southern-side of the lake. In reality, this castle is on the northern side.
Cochrane tells Gibson to try out the new bomb-sight "on the towers of the Derwentwater dam". He means the dam of the Derwent Reservoir in Derbyshire, about 150 miles from Derwentwater, which is in the Lake District and, being a natural body of water, lacks a dam.
The train showing being derailed by the flood is running on the left-hand track. British trains do run on the left, but German ones run on the right.
When the planes attack the Eder dam, they fly over Waldeck Castle towards the the dam. In reality, by overflying the castle, directly towards the dam, you would fly almost directly along the length of the dam. You would have to bank almost 75 degrees to port to approach the wall the way its shown in the film.
Shortly after the Lancasters take off from RAF Scampton (which is north of Lincoln) for the raid, they fly over Lincoln Cathedral. However they're shown flying over the Cathedral heading north (the smaller twin Cathedral towers are at the west end of the building) and back in the direction of Scampton.
The system devised to get the height right was, in the film, said to have been thought of by the 617 Sqn crews following a visit to the theater. In reality it was devised by the 'boffins' at Farnborough.
Before the raid, the Lancasters are shown being loaded with machine gun ammunition. The bullets being loaded are 50 calibre, while the Lancasters, at that time, only used .303 calibre machine guns.
Some crew are seen to be entering the Lancasters prior to taking off wearing normal walking shoes instead of flying boots.
Bomber Harris normally wears the cap of an Air Chief Marshal (with 2 rows of scrambled eggs). In a scene at Reculver his cap has only 1 row (the cap for Air Commodores and Group Captains).
Before the first successful bomb test, Gibson tells Wallis that there is a new moon and he should make a wish. He isn't referring to a calendar new moon when the moon is invisible, but rather the first appearance of a thin crescent, the sight of which traditionally prompts a wish. But as Gibson says it, they look in the direction away from the sun, which is behind them. A "new moon" of this kind is always close to the sun, visible low in the sky after sunset. So in any case it shouldn't be visible with the amount of daylight seen.
In two shots of flights of three Lancasters taking off on the mission, each has a gap in the ventral fuselage where the bomb should be. Later shots of the bombers in flight have the weapon showing as a semicircular bulge in the same place - the silhouette of the bomb was presumably added in post-production, with the take-off sequence forgotten about.
The Lancaster shown flying over the Derwent Reservoir is not a Dam Busters aircraft, in that it has bomb-bay doors and a mid-upper turret, both missing from the AVRO Lancaster Mk.IIIs Type 464 (Provisioning) aircraft used in Operation Chastise.
When in the upper briefing room where Gibson is addressing his crew, on the right hand wall is a painting that depicts the actual briefing taking place.
Guy Gibson is smoking a pipe in a first class railway compartment. The pipe smoke goes out of the window towards the engine i.e. in the opposite direction to what it should.
The "full size tests" show a de Havilland Mosquito dropping a Highball prototype from a height very much greater than the 150 feet mentioned in the script.
In a shot of the airfield, its shows three Lancaster's and one Avro Lincoln, (the successor to the Lancaster, which first flew in 1944) in the shot.
In a scene showing the airfield at RAF Scampton, there is a silver aircraft on the horizon, in a later shot when the boffins are talking together in one of the cars, one can see an E.E. Canberra, which is in a silver finish, the RAF's first jet bomber, in the rear quarter light of the car.
The spot lamps are positioned at either end of the plane so that the beams would cross at a certain height however during the testing the beams are clearly parallel to each other which means either the lamps are not in a straight line from each other or the aircraft is flying side ways.