Training units
Barracks, War Factories, Shipyards and Airfields turn money into forces.
Open a production building in a base and order units. You pay when you order, and each building trains one unit at a time from its queue.
Queued units can be moved up or cancelled. Switch on Repeat and the building keeps ordering the same unit again, as long as you can pay.
Without power, training pauses and later carries on where it stopped. A base under attack keeps training while it has power.