I wish the instructions would give more information on forming combos. Since they didn't, you can follow this link and see all the possible combos, along with pictures of the turrets for those who don't want to work so hard as to put the name with the right turret. I recommend using the nuke first. The two cannons plus the rocket give a HUGE kill radius destroying everything. The two cannons also form their own combo with landmines for those units the nuke misses. http://onslaught.playr.co.uk/about.combos.html
Two of the huge blobs attacking me... What to do? Oh, .50 cal box gun! (Press A) Wait for box gun to deploy... BAM shoots me instead.... I hate friendly fire :(