Yankee Doodle Dandy (1942) is one of Hollywood's greatest, grandest and slickest musicals. The nostalgic, shamelessly-patriotic, entertaining film also supported the war effort as it paid tribute in its mostly fictional story to [George M. Cohan,] a popular Irish/American entertainer and the grand American gentleman of the theatre in the early 20th century.
The timeliness of its release, just after the attack on Pearl Harbor in late 1941, helped the 'propaganda machine' of going to European battlegrounds overseas with a song that was a rousing theme song written years earlier for WW I - Over There. And a second song, You're a Grand Old Flag, contributed to morale-boosting, flag-waving patriotism and love of one's country. And it was the first time that a living US President (FDR in this case, played by Jack Young) was portrayed in a motion picture.