A statue of Father Francis Duffy stands in Times Square in New York City.
The "Major Donovan" character was based on "Wild Bill" Donovan, who was awarded the Medal of Honor in World War I, and as Major General Donovan was the Director of the Office of Strategic Services (OSS, forerunner of the CIA) in World War II.
James Cagney's character is heard to share several words in Yiddish with a fellow soldier early in the film. Cagney was a fluent speaker of Yiddish, having been raised near a Jewish neighborhood in New York City.
In training camp, there is a reference to the 69th as "Coxey's Army". This was the name given to a protest march on Washington in 1894 by unemployed workers, led by businessman Jacob Coxey.
The poem read at the funeral of the soldiers killed in the dugout is"'Rouge Bouquet" by Joyce Kilmer (portrayed by Jeffrey Lynn). This scene and preceding ones are based on a true incident in the war, when a German heavy artillery bombardment on March 12, 1918, buried 21 men of the 69th; 14 of the bodies were never recovered.