In the first Japanese mission, you will need to sink Henry Walker's PT-23 and shoot down Donald Locklear's P-40, both from Battlestations: Midway. PT-23 starts on the far side of the battleships from your spawn point at the beginning of the mission. Note that there are 4-5 other PT boats in the mission, but this is the only one that is identified as PT-23. It is easiest to attack this target prior to any of the parked planes, right at the beginning of the mission, but it can be sunk at any time prior to mission end and it will count for the achievement. If you choose to wait, it will circle the island the airbase is on and shoot at Japanese planes.
Donald’s plane appears in the fourth and final phase of the mission when you are told to shoot down five planes. The objective planes appear as light blue on your tactical display. Donald’s plane is not an objective plane (so will not contribute towards the five planes you need to destroy) and is dark blue on the tactical display. He generally spawns about 10-12 seconds into this phase at high altitude, and dives immediately to attack the Japanese forces. It may be easier to earn this achievement on Veteran since Donald will be less likely to be shot down by your wingmen or other Japanese forces.