Save Marines on Sacred Icon

In order to Save Marines on Sacred Icon, you will need the Sputnik Skull. Play the level until you get to the part where you hear the Marines saying something along the lines of "Get it offa me! Suppressive fire! Suppressive fire!" At this point, grenade jump across the gap to where the marines are. This is very difficult to pull off, as a single hit from any Flood form will kill the marines. However, if some manage to survive, you will notice that, unlike in the level Great Journey, the marines are your enemies (this is the only way to fight marines without betrayals or mods). This is a glitch/secret that allows you to save some anonymous Marines on the level Sacred Icon.

http://video.google.com/videoplay?docid=-965550901904090705&q=save+marines+flood