Build nothing but shooters and camp out by a concentration of stables, preferably near an Acropolis. Don't worry about stars or loot, just shoot stable troops. When they get close, rally away from them.
Let the stable spawn cavalries once or twice before taking out the stable. Instead of one you can get at least 7. I’ve done about 12-15 of course it’s easier with jets taking them out from above. I finish my 1400 kills in a day and a half.
Drop medals and hit a lot of easy bases. Minimize troop losses and you can hit 15 in an hour, averaging 15 tanks/depots per base. So 7 hours play will get you to the CWA goal of 1550. And a ton of resources to boot.