I've been running HoI2 vers 1.3a patched on a 1936 scenario. I have researched up through Airborne '45 (Par-4) and Douglas C-54 (Tra-3) for my trooper/plane combo. I have "Battlefield Interdiction Doctrine" researched to enable Airborne assualts. Selecting the plane unit (4 Tra-4's) I don't recieve Airborne Assualt as an option, only "None" and "Air supply". I have saved and completly exited game since it should have been enable and am I unable to perform the Assault mission. I've never dealt with paratroopers before in any game I've played so don't know if this is a problem or I'm just being noobish.