appearing in The War Lover) and flown by him, also appears in the film, dropping Bergman back into Norway. The director and former Mitchell bomber pilot Walter Grauman flew the B-25 himself, acting as co-pilot in the right-hand seat. During filming, technical advisor Hamish Mahaddie, who had acquired the aircraft for the film, told Walter Mirisch he "commanded the 14th largest air force in the world". Special effects Although the film made extensive use of real flying aircraft, special effects were needed to create the final attack scenes. Oscar winning special effects technician Tom Howard used miniatures, front and rear projection and matte paintings to make the sequences work. Cliff Robertson enjoyed working on the film and stated that the atmosphere on set was very good, but was unhappy with the ambiguous ending. He noted that the movie was shot on a very tight schedule and budget. He regretted not being allowed to pilot a Mosquito, which he was forbidden to do for insurance reasons. Differences from the book The film and the novel on which it was based follow the same basic plot, but many details were changed for the film. Some scenes were re-arranged in sequence and the story was heavily condensed with most of the characters' backgrounds not mentioned. The first half of the book sees the squadron equipped with Douglas Boston light bombers before converting to the Mosquito. An early coastal shipping strike sequence was omitted for the film, as was an action packed reconnaissance mission. The film adapts only the second half of the novel. In the novel, Squadron Leader Roy Grenville was a British character, but becomes Americanised as Wing Commander Roy Grant for the film. Robertson, a U.S. actor, was cast because he was popular internationally at the time and because an American central character improved the production's access to finance and worldwide audiences. Additionally, Robertson was an experienced pilot, owned a Supermarine Spitfire, and was personally interested in making the film as an accurate portrayal of wartime flying. Although he was refused permission to fly for the purposes of the film, his scenes stand out as a realistic depiction of operational flying. At the end of the film, it is unclear whether Grant survives the mission or not. However, in the book Grenville does survive but becomes a prisoner of war. In the novel, much more time was devoted to the personal