Total Annihilation - Arm Mission 6 Epic Fail on Hard Difficulty 

Damn this mission is a pain in the ass.
When playing the TA campaign, the AI cheats pretty harshly. This mission is particularly difficult, since Metal resources are extremely scarce, and the AI basically uses a map hack, and uses very long range missile launchers periodically on your metal extractors after just 15 minutes elapse.
The strategy guide for this mission is to mass crusaders and lurkers which are suppose to deal with the long range attackers.