Michael Powell forgot that Newfoundland was a Crown Colony and not a part of Canada, and when they moved the full-sized submarine model there it was impounded by Customs & Excise, which demanded that import duty be paid. The matter was finally resolved when Powell appealed to the Governor of Newfoundland, citing their work for the war effort. Newfoundland finally became a Canadian province in 1949.

Elisabeth Bergner was originally cast in the role of Anna. Initially the Hutterites were only too happy to assist with the filming until one day Bergner was spotted by a Hutterine woman smoking and painting her nails, which so incensed the woman that she slapped Bergner full in the face. Filming was halted until Michael Powell pleaded with the community to let them continue. Bergner was eventually replaced by the much younger Glynis Johns (although Bergner can be seen in some long shots). It also transpired that the main reason Bergner had joined the film was to get to America-as a German Jew living in England, she obviously felt that the Nazis were a little too close for comfort.

Peter Cushing had gone to Hollywood before the war, but things hadn't worked out too well, and he ended up doing a variety of odd jobs, which is how he came to be making props (not acting) on 49th Parallel. One day he had the job of making flags for model boats to be pushed around a map, and he made a lot of swastikas and laid them out in his digs. They were found by his landlady who promptly called the police.

Emeric Pressburger said, "Goebbels Josef Goebbels, Nazi Propaganda Minister considered himself a master of propaganda but I'd thought I'd show him a thing or two". Ironically, Pressburger's status in Britain at the time was as an enemy alien, so when he returned from filming in Canada he found himself imprisoned and threatened with deportation. Thanks to the intervention of Michael Powell and the Ministry of Information, this did not happen.

Esmond Knight was first choice to play Lieutenant Hirth, but he had enlisted in the Royal Navy at the outbreak of war.

Anton Walbrook donated half his fee to the International Red Cross.

Raymond Massey, Leslie Howard and Laurence Olivier all agreed to work for half their usual fee for the war effort.

Raymond Lovell nearly drowned in the scene where the seaplane crashes in the lake as he couldn't swim and the plane sunk a lot quicker than anticipated.

According to the book 'The Golden Gong - Fifty years of the Rank Organisation, its films and its stars' by Quentin Falk, the Rank Organisation stepped into save the " . . . wartime propaganda film '49th Parallel' when Ministry of Information money ran short of completion."

According to the book 'The Great Adventure Films' by Tony Thomas, "The grand title '49th Parallel' - referring to the line of latitude dividing much of Canada from the United States - is misleading since the film is not about American-Canadian relations, and the only point in which Americans are involved occurs at Niagara Falls, which is not on that latitude."

According to the British war film documentary episode The War Game, the World War II film 49th Parallel's " . . . main message was to pluck the conscience of the neutral USA to come to the aid of Britain in the Second World War."

All of the opening travelogue was shot by Freddie Young with a handheld camera out the windows of trains, cars and planes.

Although this film was nominated for 3 Academy awards, the title 'The 49th Parallel' is no where to be found in Academy records. That's because it released in the US as 'The Invaders', which is how the Academy has it listed.

Commissioned by the Ministry of Information to raise worldwide awareness (American in particular) of the Nazi threat. However, it was intended for Canadian consumption also, as many French Canadians did not want to be at war with Germany and did not want to fight. Vichy France was an ally of Nazi Germany, and many French Canadians in Quebec were pro-German. One of the reasons Laurence Olivier, the biggest star in the film, played a French Canadian trapper named Johnny who tells the Nazi officer he is a "Canadian" in the film and not "French" was that it was intended also as propaganda to promote pro-British feeling in Quebec. When Canada resorted to conscription to swell the ranks of its Army, there were draft riots throughout Quebec, so intense was the feeling against the United Kingdom, which of course had subjugated New France less than 200 years before. Anti-war sentiment was so rife throughout Canada, Prime Minister William Lyon Mackenzie King declared that only volunteers would be shipped off to Europe.

In the final scene of the film, showing the box car carrying the German sailor and Canadian soldier being returned from the U.S. to Canada, shows the train moving backwards right to left over the Niagara River which is flowing towards the screen. This is a geographic impossibility: the Niagara River flows south to north, with the U.S. shore always west of the Canadian shore. As a result, the film shows the train moving from Canada to the U.S.; a correct shot would have shown either the train moving left to right or the river flowing away from the screen.

The 49th Parallel of the title is the circle of latitude 49th parallel north or 49 degrees north. As the film mentions, it represents the border between USA and Canada, the latter of which where most of the film takes place. The 49th Parallel also crosses Europe, Asia, the Pacific Ocean, North America, and the Atlantic Ocean.

The book 'The Film Business - A history of british cinema 1896-1972' by Ernest Betts states that this film " . . . is one of the first large-scale attempts at fictional propaganda by the British Government during World War II. It was partly financed by the Government and was given top priority and a prestige send-off by Vincent Massey, High Commissioner for Canada, where the film was made. No other project of the war was so boosted. Money, publicity and stars were unstintingly forthcoming - Laurence Olivier, Eric Portman, Leslie Howard, Raymond Massey, Anton Walbrook and Elisabeth Bergner. Of the film's budget of £130,000, £40,000 was supplied by the taxpayer. On location it soon ran into difficulties. Miss Bergner left the picture after a disagreement over the part she was playing. Efforts to persuade her to return were unsuccessful and she was replaced by Glynis Johns."

The British national press complained about the film's sympathetic portrayal of Nazis. Emeric Pressburger's rebuttal was that there must be reasonable Germans as well as ruthless ones. Michael Powell joined in by writing a letter to The Times, defending the film's stance. At any rate, it didn't impede the film's success - it was the biggest grossing film in the UK in 1941, and the biggest grossing British film to date in the US.

The depiction of U-37 in this film is fictional. U-37 has no known sailings around Canada, or what was then still a Crown Colony, Newfoundland.The real U-37 was the second most successful boat of the war (U-48 having the highest score) and was eventually scuttled on 5th May 1945 at Horup Haff, Denmark despite the sinking depicted in this film.

The film's dedication states: "This film is dedicated to Canada and to Canadians all over the Dominion who helped us to make it; to the Governments of the U.S.A., of the Dominion of Canada, and of the United Kingdom, who made it possible; and to the actors who believed in our story and came from all parts of the world to play in it."