Having done the same research myself, I came to the conclusion that far too many sources make assumptions. You will notice my careful wording. The 2pdr AT gun was never issued with a HE round.
I fully believe that they were manufactured, as performance descriptions are available, and the effect of a 2pdr HE shell is compared to a mills bomb.
So not a lot of use and, because of this, it was
decided not to issue it.
On the subject of airborne HQs. During the entirety of WW II, it was done
once. The article I pointed to seems to imply that it would have been far better use of the gliders to have deployed more fighting troops.
Considering the benefit of a Corps Commander is improve the reinforcement chance of his divisions, under the circumstances I can’t think of a less useful HQ ability to have.
Unless it’s the actual leader bonus you’re after.
It’s a very easy fix though.
All you need to do is go to the Units folder, scroll down until you find hq_brigade and open it in Notepad.
Just under where it says “is_buildable = no” and the line
can_paradrop = yes
Close & save. Job done.
Unfortunately, this will allow
ALL HQs to be air transportable. Not all that realistic but you could always go the whole-hog & create a new unit type. Air_droppable_HQ.
It shouldn’t screw the AI up because it’ll never know it can transport HQs by air. Maybe it’s cheating, I don’t think it is. It’s allowing something that actually was done right?
It’s a lot of effort to allow a unique event though.
I mean, why aren’t marines parra-dropable? The Yokosuka SNLF brigades all conducted more combat-drops than the Japanese Army parachute units.
And there are many many more things that need fixing before allowing that
ONE HQ to be air-dropped.
IMHO of course
EDIT:
@Count Blue Does Black Ice allow the IJN to have SNALF?
(Special Naval Air-Landing Forces)
Edit2: Why are there IC costs & build times for a HQ?

And what makes the exe recognise it as a HQ? Because it's
created as one? Or because it's got a radio strength of 2?