Got it. Thanks for the clarification. It’s funny how once the rule is clarified, it makes total sense…
The rule says there needs to be “at least one Defending unit.”
Can I assume that means I need to have an undamaged Airbase and at least one Fighter in the zone under attack before Fighters in adjacent zones can scramble and assist? Having a defending Factory, or a defending Land Unit aren’t an option? Or could I place 3 Fighters in Berlin, 3 Fighters in Western Germany, and those 6 Fighters will scramble to protect all 4 zones?
So to get around the rule, the UK could raid and damage the Airbase in E. Germany. Then, the US (before Germany have a chance to repair their Airbase) could raid the Factory in the same territory, and not only would any remaining E. Germany Fighters not be able to scramble, but no Fighters in adjacent zones would be able to scramble since there are no Defending units?