This achievement must be obtained during the "Raising The Flag" mission in Act II. The mission is a breeze on easy, and I'd recommend using the Grumman TBF-1 'Avenger' since that gains you an extra medal.
This mission has three parts: first you have to destroy the artillery on the mountain, then you have to destroy three groups of three tanks each. Both of these parts are very easy if you use rockets - for the artillery, just shoot all four rockets on a target and then move on to another target, and any group of tanks can be destroyed with one well-placed rocket (imagine what four will do).
Part three of the mission is about getting this achievement. Kamikaze pilots will attack the fleet and you'll have to shoot them out of the air. There are three volleys of several formations, with three planes per formation. Keep targeting them with Ace mode (switch targets with LB if the game gets confused and tries to put you on a secondary target) and this should be a cakewalk.
Now here's the important part: You don't have to shoot down every single kamikaze. Every formation has three planes closing in on the same battleship but just about every formation targets a different ship, so get at least two out of three planes per formation and you should be fine. You'll only have to restart if one of the battleships is destroyed - you'll be notified by a message saying "secondary objective failed - protect all battleships".