What about Battle of Metisette? The Rubble? Back in 2535 when the Spartans were still getting tazed by Mendez for falling asleep in class on how to treat their own sucking chest wounds.

A prowler full of ODSTs and Lt Keyes pretty much totally owned an entire solar-system [url=http://halo.wikia.com/wiki/Prophet_of_Truth#Battle_of_the_Rubble]and set Prophet of Truth's plans back about a decade or two[/url].*

*Unofficially, they had help from a certain AI, and a few renegade Spartans (they didn't really have a mission, and just happened to be there drinking the local beer).