Fireteam 4

"Command HQ, this is Fireteam 4. We are pinned down in Alpha Lab."

- Fireteam 4, reporting at the outbreak of the demon invasion

Fireteam 4 was a team of marines stationed on Mars City in Doom 3. When the demons invaded Mars, Fireteam 4 ended up pinned down in Alpha Labs. It is highly unlikely they survived, given that Alpha Labs was overrun and they were not heard from after their report to Command HQ.