The music playing in the background when Frank has his flashbacks is Samuel Barber's "Adagio for Strings." More specifically, the piece by Samuel Barber (1910-1981) was originally the "String Quartet op. 11" (1936), from the second movement ("Molto adagio - attacca"). But, within two years, he arranged it for string orchestra and entitled that simply "Adagio for Strings". It has since become an unofficial American anthem of mourning.