From Halopedia, the Halo wiki
During the Battle of the Etran Harborage, Bravo Platoon, along with Alpha Platoon and Charlie Platoon, was left on the planet's surface, trapped behind a region infested with Flood structures and biomass, when the UNSC Spirit of Fire was being pulled into the one of the many portals that connected the Shield World's surface to its interior. Under the leadership of Sergeant John Forge and Captain James Cutter, UNSC ground forces were able to destroy the Flood infestation between the three platoons and UNSC firebase, securing an escape path for Bravo Platoon. While the first two platoons returned to the UNSC Spirit of Fire through D77-TC Pelican extraction, the third platoon was forced to fight its way back to the firebase on foot. Regardless, all surviving Marines in Bravo Platoon returned to the UNSC Spirit of Fire.
Bravo Platoon is one of the three platoons players need to rescue in the Halo Wars campaign level Shield World. They can be saved in any order, and if Bravo Platoon is one of the first two platoons to be rescued, the player is rewarded with the Elephant, which cannot be made in the firebase.
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