Where are all the enemy labs located?

So recently I found that in Advance Wars 2, there are secret missions you can go to by capturing some specific cities.

Which cities I should capture in order to unlock the secret missions?

Solution 1:

There are four city need to be capture in order to play those mission. Below I will list down the city at need to be capture and also show you which mission the city located at.

Orange Star

On the Mission 4: Flak Attack, you need to capture the city (Red circle marked) in order to get the enemy lab map.

Blue Moon

On the Mission 10: Toy Box.

Yellow Comet

On the Mission 19: Show Stopper. Capture the this city will unlock the secret mission.

Green Earth

On the Mission 26: Sinking Feeling. Go to the island and capture the bottom city will unlock the secret mission.