You can paradrop your paratroopers into friendly territory, including territory you just captured, as long as you are at war. I know you're probably thinking along the lines of transporting non-para infantry, but this is something at least.What is missing in game is the ability to use transport planes to air transport troops between the airfields. That was possible and done during WWII. For example during the Battle of Crete, German Paratroopers were first paradropped into the island, but then after capturing an airfield, a Mountain division was air transported by Ju 52s into the airport.
I actually used this ability to evacuate my paras from Moscow via the nearby airfield when it become clear that the airborne army I dropped there was going to succumb to Soviet forces. I managed to get about 15 of 20 divisions out this way. The remaining 5 had to stay behind and bravely sacrificed themselves, but the others lived to take part in a later repeat of the operation which succeeded in linking up with the main front.
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