West Side Story supplies the melody interpolated in the opening of Metallica's “Don't Tread on Me.”
The opening of the song uses a melody associated with “America,” a number from the musical West Side Story. Leonard Bernstein composed the music for West Side Story, while Stephen Sondheim wrote its lyrics.
Metallica placed the brief reference at the start of a song whose title alludes to the Gadsden flag and its “Don't Tread on Me” motto. The juxtaposition gives the track a recognizable theatrical opening before the band enters with its heavy arrangement.
This detail is sometimes described simply as an interpolation of “America,” which can make the answer seem like the song title rather than the musical. The more specific source work is West Side Story, first staged on Broadway in 1957 and later adapted into acclaimed films.