315th Legion

The 315th Legion was a unit of about 9,000 Phase I and II clone troopers. They fought in the Battles of Utapau and Felucia, though mainly used as soldiers to fill gaps in the line, or to protect vital locations. A few days after Order 66 was given out, the 315th was sent to go knocking door-to-door searching for any Jedi that may've survived the order.

Post-Clone Wars
After their battles in the Clone Wars, the 315th Legion was turned into the "6th Royal Guard Legion" in 16 BBY. They were later sent on an "unknown mission" to Tatooine sometime between 14 BBY and 0.5 BBY. The unit was later disbanded due to "lack of personnel". It has since been speculated that the 315th was sent on a mission-gone-bad, or went into combat with the Rebel Alliance and took enormous casualties.