This is the first part of the Medon operation. 
The aliens are assaulting the Medon Fuel Base and stand poised to cripple the human war effort unless they are successfully repelled.
The Medon Fuel base has only a single, large entrance in the south end of its compound.  The aliens are basically unable to directly assault it from any other side.
The base's current defenses consist of two Statonex Autocannons and a single Voltar Sar-1 Shuttle.
For the Protectors to maintain the war effort 70% of all equipment and fuel storage buildings must survive the attack.