Slitherine

I'm playing Allied Corps and thought I just needed to purchase a paratroop unit and I would have the ability to "embark" from a friendly airfield. That doesn't seem to be the case.
The manual says nothing about how to "load" paratroops into a transport. I'm sitting on a friendly airfield, but no option to embark. Transports don't appear to be available on the purchase menu...
Help?

You can embark the paratroopers on a friendly airport. You need to make sure there is no other friendly air unit above the airfield at the same time tho as two air units cannot share one hex and it blocks embarking of the paratroopers. Another thing preventing you from doing so may be the lack of available air transports. Each scenario have a predefined amount of air transports set and once you used all you can't embark more paratroopers until you unload some and free the transport up. Some scenarios tho have no air transports available at all in that case sadly you can't transport your paratroopers by air and they are just normal infantry.To see how many transports you have left hover with the cursor over the embark button and a pop up appears where you can see the amount of air, ship and rail transports available.

Ok, thanks.

I'm playing the Cauldron scenario and wanted to insert some paratroops to reinforce the surrounded garrison.
I guess that's not an option. Flanking the German line to the south seems to work fine.

If you want to get some units to reinforce the 150th fast you can use the gap in the crevice on top of the map. Some fast units can reach the 150th this way in around 4 to 5 turns maybe.