Maybe all the aircraft techs could be unlocked by an event:
"Wright Brothers make first heavier than air flight"
Before that event no aircraft research is possible as everyone knows that God didnt intend for mankind to fly.
This event could fire randomly between say 1890 and 1912
Edit: In HOI terms it could consist of a tech that is dependant on knowledge of itself, that allows for further aircraft research (with other dependancies of course). This tech is then given to all nations in the world when the event fires. Maybe only to the nations above a such-and-such techlevel.
"Wright Brothers make first heavier than air flight"
Before that event no aircraft research is possible as everyone knows that God didnt intend for mankind to fly.
This event could fire randomly between say 1890 and 1912
Edit: In HOI terms it could consist of a tech that is dependant on knowledge of itself, that allows for further aircraft research (with other dependancies of course). This tech is then given to all nations in the world when the event fires. Maybe only to the nations above a such-and-such techlevel.
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