Paratroopers?

There is a unit called Paratroopers. These guys can land in enemy territory from planes without attacking any provinces

Are you sure it wasn't a rebellion? Check the newspaper.

If it is not paratroopers or rebellion, then there could have been a gifted province followed by a bunch of gold being used to make facilities and gold-speed units there.

I was thinking of units that can travel by plane as transport...

Well... now I want to suggest the idea of paratanks.

Wait what? I don't think WWII has the technology to carry a tank!

They did try flying tanks though, and paratroopers were able to come with jeeps and other small mobile equipment

Yes, maybe some small units. But think about it, should we also have transport planes? They should only be able to carry small amount of units and will have the same thing as transport ships. They will need to embark for a period of time, they will need to be researched, they will need to be disembarked. Sometimes, they can carry light armoured vehicles, not tanks. But it will take more time for embarkment. In this case, embarkment will mean having planes going to and from the destination carrying units. For infantries,, you might only need 50 planes to carry a division, for tanks, you will need more because one plane can carry one or 2 planes can carry one including the few infantrymen.