Lament for Pvt. Jenkins
From Halopedia, the Halo wiki
Lament for Pvt. Jenkins is the twelfth piece included in the Halo: Original Soundtrack.
The piece is a tense, moody ambient song by string orchestra. The piece opens with a dark, powerful drumbeat, followed by an apprehensive minor chord. Every seven seconds, the drum sounds again, punctuating a change in the chord. The song becomes increasingly disjointed towards the end, featuring the scrambled high notes typical of the Flood, and slowly fades out, leaving a dark air to the scene. The piece is remastered into A Private Service in the Halo: Combat Evolved Anniversary: Original Soundtrack.
It can be heard: