12-9F5

12-9F5 was a Scorpion Tank built by the UNSC. It had a chess piece painted on its front left tread cover, a black chess piece that appears to be a Knight.

In 2552, the tank was assigned to the frigate UNSC In Amber Clad. That year, during the Battle of Earth, Commander Miranda Keyes ordered that a tank be sent to the Master Chief in Old Mombasa to help fight Covenant forces that had landed in downtown New Mombasa. The Chief used the tank to cross the main bridge to the downtown area, destroying numerous Ghosts, Wraiths, and Banshees along the way. However, he was forced to abandon the tank soon after in a highway tunnel, because debris in the tunnel prevented the tank from going any further, due to its size.

Trivia

 * The tank will sometimes appear with an ID of UE8-14 on Easy and Normal difficulties, but will most often will appear correctly in Heroic and Legendary. Why this is the case is unknown.
 * Some of the tanks used in Halo 3 multiplayer (via Forge) bear the ID "12-9F5". However, the chess decal is replaced with a scorpion decal, and is a Halo 3-era Scorpion (with a separate seat for a gunner). Thus, it is unlikely that they are the same tank, although the tank could have had an overhaul, but this is also unlikely.
 * It is possible to drive the tank past the barricade in the tunnels with a Warthog and a little patience. However, you will soon be forced to abandon it anyways, as you have to go into the sewer system to get to the next area.