Bases, composed by Kazuki Muraoka, is the background music played the two bases of Contra. The title is unofficial.
Bases is played in each of the two bases in the arcade version.
In the NES port, Bases is played in Base 1 and 2 which are stages 2 and 4. The stages function a bit differently in the NES port. You no longer have to turn down the path, and you no longer have a time limit.
This song is one of the four tracks featured on the Konami Music Classics Collection album with the title Labyrinth Fort 1, which is an odd title since there isn't a Labyrinth Fort 2.
This song is the same throughout every region and the PlayChoice-10 release.