I've got an idea for someone to write a story.
This takes place on Harvest, when the Covenant first attack. The Covenant will land on Earth, and kill most of the Humans. The Military try to fight them off, but fail. they are forced to abandon Harvest. They leave the planet and set random slipspace coordinates. They arrive at Halo Installation 07. Unfortunately, their communications malfunction, and they land upon the ring. Their ship is destroyed, and they have to simply survive upon the Ring. None live to tell the tale; so the UNSC never finds out about Halo.