You must destroy four Jet-type arms forts. The enemy units are black, rather small AFs armed with plasma cannons and lethal, over-sized laser blades. The only weak points of the Arms Forts are the small ventilation shafts on top of the armored shells. The holes are large enough for a NEXT to enter, and also provide good cover from the plasma shots and laser blades of the Jets. You should take just a couple of hits from the cannons of nearby units. To get an easy S Rank, just fly into these holes and fire at the shafts with everything you have.