Y'know, I can't figure out if I'm lucky as hell, or the majority of this community doesn't know tactics.....
I have waltzed through this game numerous times, and not once have I met a mission that I couldn't beat, an enemy that was too hard, or an Arkfall I couldn't win. Maybe I'm just lucky, but it seems to me that some people just lack the skill required to play this game. They seem to lack, to be blunt
tactics. Weapons help, but even with weapons that friends used to laugh at me for carrying because they were terrible, I walked through this story with absurd ease time and again. Only time I ever had trouble was with the final boss the first time around. Took me a solid 45 minutes to figure him out, I have since walked in and kicked his jeking arse with ease.
For the mission in question, I never had a problem, even the first time through when I failed to notice the special weapon. All I can say is to chill back, use cover, roll, ect, to avoid their fire, take out the knife guys first and avoid the big guy until he's the last man standing and then focus on him. There isn't much else to say, it's the strategy for the entire game, even against the final boss.
If you can't beat it.... Find another game? Maybe CoD would suit you better

I don't mean to be condescending, however, if you can't beat one of the easier bunkers of the game, this game probably isn't for you.