Aircraft Evolution (EP)

I finished the campaign and this was the only achv I hadn't unlocked. A good mission for easy tank kills is 28, especially if you have a max'd out level 30 plane. One pass dropping cluster bombs will net 20-30ish tanks. Without replaying any levels I was about 40 tanks short of the 500 from my campaign run (on easy difficulty)

This is also a good level for cannons if you need to grind any of those.