A group of 10 army-like teamed DOOM Marines receive a distress beacon from the Ishimura and go to investigate on a barge. The barge lands in the Ishimura's hangar bay and the DOOM Marines disembark when suddenly the barge's fuel tanks catch fire and it explodes.
The DOOM Marines have their standard loadout.
The DOOM Marines discover a notepad with a complete and comprehensive history of the Ishimura, it's purpose, the Markers, the necromorphs and basically everything else. It has been written by a mysterious and all-powerful being.
Also, at this time, the entire crew of the other ship which Issac Clarke was on is also acting as an armylike team in the medical bay and their objectives are to:
restore power in medbay
deactivate power in engine room
activate engines #1 and #3
restore power to bridge
The DOOM Marines come from DOOM 3, which shows the Marines on the mars research base.
The DOOM Marine's objectives are to:
restore power in engine room
restore power to FTL drive
successfully pilot starship back to earth where it will be studied and researched upon