The Assault Theme is a recurring music in the Metal Slug series, usually associated with Allen O'Neil due to how his appearences coincide with the theme's use. It plays in the second half of mission 2, mission 3 and during the final boss fight of Metal Slug. In Metal Slug 2/X, it plays in the third boss fight and it also plays at the first sector of the final mission. In Metal Slug 3, it is used on the Ostrich Slug path at mission 3 and on the Hi-Do mid boss battle on the final mission. It got a new remix in Metal Slug 7 and it plays as the sixth boss theme.