Fire Team Charlie was a United Nations Space Command Orbital Drop Shock Trooper unit stationed aboard the UNSC Pillar of Autumn that actively participated in the Battle of Installation 04.
During the raid on the Truth and Reconciliation, Cortana broadcasts: "Cortana to Fire Team Charlie. Move up on the left. You should be able to flank the enemy."
A different Fire Team Charlie was seen in Halo: Combat Evolved first in the first scene of level Pillar of Autumn, but were not named until the second level, Halo. This Fire Team Charlie was part of Staff Sergeant Johnson's platoon.
Connection with Foehammer
SSGT. Johnson's Fire Team Charlie seem to be in some connection with Pelican Dropship Echo 419's Pilot 'Foehammer.'. In the level Halo, Fire Team Charlie knows the pilot of dropship Echo 419 - 'Roger, Echo 419. This is Fire Team Charlie. We read you 5-by-5. That you, Foe Hammer?' .
Appearances
Johnson's Fire Team Charlie was seen in Halo: Combat Evolved first in the first scene of level Pillar of Autumn, but were not named until the second level, Halo. The ODST Fire Team Charlie was seen in the level Truth and Reconciliation, led by Sergeant Parker.
Speculation
Fire Team Charlie and Fire Team Zulu may be in the same company, maybe even the same platoon, although this is pure conjecture and not definitively or even implictly stated.
It is possible that companies contain twenty-six Fire Teams. This would mean that each company has their own Fire Team Charlie, Zulu, etc. and would explain why there is an ODST Charlie Team and a regular Marine Charlie Team.