I have found one good early mission with constant loot worth farming.
On the "Offshore Drilling Rig" the mission "Aircraft Carrier"
You hit 3x for 28 energy each and you get a boat everytime.
Chance of 3 units: Mine Ship (A1/D2), Oil Destroyer (A3/D2) or Oil Aircraft Carrier (A3/D5)
Anyone have any other loot farming missions worth hitting up, post them here.