On the 3rd level.You have to disable the the command post.You go to the baseball stadium and there will be 2 large wathching stations,one of those 2 is the command post.Then you go to the hotel(the one where the gate is locked)Then go to the next room to the left and up the stairs.Then there will be a door hiding in the room.Watch out for the enemy behind the wall. then you walk up the stairs then you will have to protect Gunny and Donnie.After you are done protecting them,go through the hotel gate then into the church,look for a way to signal for the demolition team to come backyou up.
Then you have to ride the truck and protect Gunny(Gunny is driving the truck)Then you have to kill all the enemies.(there is a lot of cans that can exploed,when enemies come near the cans,blow the cans up. Good Luck with my hint.