Watch it.
You start the video, the video first displays In white text, "Tonya Anderson Baker, Gunnery sergeant. 2642 (143 years ago)."
The start of the video shows the crash site of the "Westside", apparently it was a destroyer.
They go though the usual routine of helping the wounded, you skip that.
Two hours later five of them arrive at the same cave you are at now, and inspect a dead body.
Gs; Tonya:"Dead Lieutenant, been so for a while."
Lt; Blake:"Any idea how?"
Gs; Tonya:"Crushed, quite hard too."
Pvt; Smith:"I have a bad feeling about this..."
Cpl; Dennis:"I don't want to see what did this."
Lt; Blake:"Cut the chatter-"
*Faint roar*
Gs; Tonya:"What the heck was that?!"
Pvt; John:"Sir!"
*Lots of the things you saw on your ship come up.*
Lt; Blake:"OPEN FIRE!"
*A gun battle ensures*
*Pvt John goes down*
Pvt; Smith:"NOOOO! John!"
Lt; Blake:"Stick together dammit!"
*The fighting continues until all of those creatures are dead, Smith goes to John's body*
Pvt; Smith:"...Dead..."
Gs; Tonya:"Shit."
*The same distant roar, this time closer, much closer*
Gs; Tonya:"OH SHIT!"
*Gs Tonya gets hit across the room by a gigantic alien, instant fatality.*
Cpl; Dennis:"YOU BAS-AAAARRGHHhhhh..."
*Cpl Dennis gets stabbed by another kind of alien, he dies.*
Lt; Blake:"I'LL TEACH YOU SOME RESPECT BOY!"
*Lt Blake fires a rocket launcher, killing most of the aliens, yet having no effect on the gigantic one.*
*Pvt Smith goes down to the same aliens that killed Dennis.*
Lt; Blake:"Aw shit."
*Lt Blake gets whacked out of the cave at bone breaking speeds.*
The video ends with white text saying "Squad status; KIA or MIA, Tonya Anderson Baker, Gunnery sergeant's status; KIA.".