Here is 8 of n for discussion of my Classic House Rules
My suggested rules add new units to the game. Some powers have never produced a certain type of unit. These optional rules add a fee to the cost for these units the first time those powers produce units never seen before on their roster.
If a country does not start the game with a certain type of unit in their possession (e.g. the Soviet Union and Battleships, Germany and Aircraft Carriers) then that country is considered to be unable to make any of that type of unit. If a country wants to make a unit that it unable to do so, then that country must make a one-time payment to the back in order to build the capacity to make that type of unit. The payment is 6 IPC. Once this payment is made the country in question will be able to make that type of unit as if it had started play with that type of unit. Payment is made for each type of unit (Aircraft Carrier, Battleship) desired. Units may be made on the same turn as the payment to build the ability is made to the bank.