The end of the movie was filmed at the ruins of Adolf Hitler's Berghof in Obersalzberg. They clearly used the entry hall with the vaulted ceilings and the conference room with the giant picture window.
Gene Kelly was 40 when he made this film, in line with his character's age, while Pier Angeli was 20 when she played 18 year old Willie, thus making their romance a bit of a stretch.
During questioning at the Military Police Headquarters in Germany, a calendar for the New York Central Railroad can be seen on the wall. While this is probably seen as a mistake because the New York Central is not a Transatlantic railroad, it is possible the railroad donated many such calendars to the military overseas. Long considered one of the US's two great eastern railroads, along with its long-time rival Pennsylvania Railroad, the two giants merged in 1968 to form the Penn Central, only to be bankrupt within two years.
Charlotte Flemming's only film.
At one of the Munich nightclubs an American style quartet is heard singing a jazzy song in German. This song is a translation of "On the Atchison, Topeka, and Santa Fe," a showstopper made famous by Judy Garland in the MGM musical The Harvey Girls.