From Halopedia, the Halo wiki
The Helljumpers' anthem is the traditional song of the 105th Shock Troops Division. It features "hyped up strains"; Given the ODSTs' penchant for flip music, the anthem is likely part of this genre.
During the orbital drop from the UNSC Pillar of Autumn to Installation 04, an ODST placed a small disk into his or her data player and played the anthem over the team frequency. Neither Lieutenant Melissa McKay or Major Antonio Silva told the ODST to stop the track, so McKay concluded that was the time to play it.