Bravo Team was a Marine unit stationed on Mars City in Doom 3. When the demons invaded Mars, Bravo Team was one of the few groups of marines to survive the initial wave of the attack. The player spends the first third of the game attempting to meet up with Bravo Team. However, Bravo Team is ambushed by a group of imps and wraiths at the EnPro Plant, and by the time the player reaches their location, the entire team has been wiped out, save for a single, badly wounded marine. The surviving marine from Bravo Team gives the player a special transmission card that will allow the player to send a distress call to Earth's Fleet. Moments later, the lone survivor is attacked and killed by a wraith.
The Lost Mission
In Doom 3: BFG Edition's new campaign The Lost Mission, it is revealed that there is a survivor of the ambush, knocked unconscious by an imp for an unspecified amount of time. During this time, he is dragged away from battle and thrown into a room filled with dead bodies (possibly to be eaten later by the demons). When he regains consciousness, he becomes the protagonist of the story and embarks on a mission to destroy an experimental teleporter before the forces of Hell can use it to invade Earth.
In Doom Resurrection, a survivor of Bravo Team likewise awakens to be greeted by a UAC scientist named Dr. Garrett and his droid Sam, and is sent on a mission to reach and assist a spaceship waiting to take multiple survivors off the planet.