Fire Team Zulu was a United Nations Space Command Marine unit stationed aboard the UNSC Pillar of Autumn that actively participated in the Battle of Installation 04. They are first heard of by SPARTAN-117 about a third the way through the Assault on the Control Room when the Master Chief stepped out onto a bridge spanning a large valley.
The Pelican that transported Fire Team Zulu was attacked by Covenant Banshees on its descent to drop off the Fire Team. After deploying the troops, along with a Warthog, the drop ship flew out of view into the next valley where it was later found crashed into the valley wall. The crash was not witnessed by the Master Chief but it is assumed that it was due to the damage sustained from the Banshee attack (seen on Heroic and Legendary difficulties). Weapons that were brought in by Team Zulu include a Rocket Launcher, Sniper Rifle, and a Warthog. The Master Chief, upon meeting up with Fire Team Zulu, helped by destroying a Ghost and a couple of Shade turrets. Upon linking up with Zulu, Spartan-117, with a Marine manning the Warthog's turret, destroyed a nearby Wraith guarding the valley.
A Scorpion Tank was present near the drop ship's crash site in the next valley, but it does not seem likely to have been brought in by Fire Team Zulu as a Pelican can only lift a Scorpion or a Warthog due to weight limits. Additionally, the Fire Team Zulu Pelican can be seen carrying a Warthog from the bridge.
The tank was presumably brought in earlier by another Marine unit. Later, the Master Chief encountered Marines from a previous mission. Cortana announces their presence by saying, "I thought the Covenant had eliminated all Marine forces in the area". These Marines were probably not part of Fire Team Zulu, because the teams were nowhere near each other. They could, however, have been part of the same platoon or company.
Fire Team Zulu then assisted the Chief as he fought his way through the valleys; when the Master Chief had to ascend the final main valley in order to cross a pair of bridges overlooking the valley, they did not follow because evac had become available.
The surviving members of Fire Team Zulu were either likely consumed by the Flood or killed when Installation 04 was destroyed , though it is possible that some could have survived and left Installation 04 with Pete Stacker.