A little question

[Charlie Brown]

so i've been playing this really interesting first mission of the allied campaign for like 2 hours and i stumbled upon this problem that is causing me to go crazy-->how in the name of god do you eliminate those guards in the ammo dump (or a fort or however you call it)? i was able to get to it and eliminate the two guards that are at the back...then i eliminated the one patroling the perimiter, then moved my troops in...and now i can't figure out a way to eliminate the others without making them sound the alarm...and it is driving me crazy (a good crazy though very addictive game)...anyone got any ideas on how to do that?