For our design phase, according to the relevant post by Sensei, these are the costs for using aluminum. Because we stole their industry, I mean, so we should know how to use it.
Craft can be reinforced with aluminum (+1 ore) or be built mostly from it (+2). Aluminum engine blocks costs +1 ore or are free in aluminum craft.
Might I suggest designing a Struunk II to replace our Struunk I, one reinforced with aluminum? Bluntly, the Struunk I is a really aging design by this point, being the first vehicle we ever designed. Making a new armored car to replace it should hopefully give us something to counter the enemy autocannon cars, and by using aluminum in its construction we hopefully will be able to afford to mount some real armor on it.
On the other hand, it might be worth trying to design some sort of attack boat to kill their new cargo boat that is giving them another damn resource point. But I'm inclined against it, we really need to stop their march on our capital first.
Or for a more out their idea, we could design a dedicated fast bomber built from aluminum. If we could get something that costs, say, two oil like the Model 1 Biplane and then two ore for being built mainly from aluminum, we could afford to mass produce it, and according to the latest battle report the main reason their flack is working is because our current bombers are on the slow moving side. And a light aluminum bomber could probably move pretty fast if designed right.
Personally my inclination is for the fast aluminum bomber, but what do other people think?