During the Onslaught mission, the best strategy for surviving the Derm Forces is to simply repair the generator, then repair the two turrets. One is on a hill and another is up towards the roof opening. After that is accomplished, go up to the roof opening where the flag is located in the capture the flag games, Then, go to the nearest Inventory Station and select Medium Armor. Select your pack as Remote Turret. Deploy two turrets on each end of the turret side of the base and deploy a few more where each opening to the basement is located (near each of the Inventory Stations). Then, hide and let your Mortar Turrets (you should have switched them at the beginning) and Remote Turrets do all the work. After the first wave is over, switch to the Heavy Armor (Juggernaut Armor) with a Shield Pack (activate it frequently).