The enemy at sea strategy

Lincoln 3, The enemy at sea
My strategy for how I did this lvl
Put 2 income, stable, and range princess on starting buildings. Produce Gatling guns and armored cars from there each turn. When unable to afford both, produce armored cars.

North group
Genghis, Caesar, and Napoleon focused attack on the artillery general over the mountain. Armored cars can clear the other artillery unit. The artillery general will move across the sea to attack the base Lincoln is in, follow him and finish him. Next capture the nearby factory and range. Move to save your ally by killing the attacking British generals.

South group
Capture the buildings near. Kill the tank general and clear any other units near the buildings. Move east to your ally's base. Just focus attacks on the 2 artillery generals. Once done I sent the general expect Alexander north to support the north group. Gatling guns stay at ally's base.

Note: If you kill all enemy units than the lvl will end but you will only get 1 star even if you keep all your objectives alive. Be sure to keep some enemy units alive for 3 star. Keep a bit more alive than me as ally nearly killed them before the lvl ended.