One Final Effort is a song included in the Halo 3: Original Soundtrack. It is heard on the level The Covenant at the start and when you face the two Scarabs. It is the third movement of the Covenant Suite.
It starts with a piano playing the theme from This is the Hour. It then switches to the Halo 3 version of the Halo Theme. The end is a soft string melody that fades to a close. Furthermore, this song also seems to be a remake of Unyielding from Halo 2. Also, a large part of this song is used as part of the Truth and Reconciliation Suite.
The song plays at the beginning of The Covenant, and during the Scarab battle. A different version, one that is more true to the original Halo Theme is also featured during the Warthog escape in the level Halo.
This song could be a reference to the Prophet of Truth's quote and Lord Hood's quote, which both say 'One final effort is all that remains'. It runs for 3 minutes and 59 seconds.
- At the end of the Halo 2 level High Charity the Prophet of Truth can be heard saying "If you are to falter, know this: One final effort is all that remains."  This may imply that the Prophet of Truth is encouraging the last troops of High Charity to commit suicide rather than be killed by the Flood, though this would not prevent infection, or it could refer to the activation of Installation 05. This line originates from dialogue recording sessions conducted pre-Halo where Jaime Griesemer is directing Jason Jones in a painful attempt at a Scottish accent. An mp3 of the clip is available on Bungie.net media player 
- Additionally, at the end of the level Tsavo Highway, Lord Hood tells the Marines "One final effort is all that remains." He is referring to the final defeat of the Covenant. Incidentally, this song plays during the battle outside the Citadel, regarded as the Covenant's last stand. As such, this track plays during the UNSC's 'final effort' to defeat the Covenant.