This is on Hard/Normal, BTW. Otherwise, it wouldn't be anything special.
Well, I can't agree.
Your first frantic post of "Not working. And he is getting heavily counterattacked" shows no counter-attack at all on the PAR but rather a PAR that landed in on a battle which he never should have entered. No, the enemy did not get 7 more units in there. Rather there are 7 units in Portsmouth and Bristol supporting the defense of Plymouth, best I can tell.
Next, you should not have flown the PAR while the Plymouth province display said only 1 enemy unit. As long as any enemy unit is still defending in the province , then the addition of a PAR will immediately introduce to the defense all enemy currently moving to reinforce that defense, or supporting defense. You are lucky you had a very good offense from the amphibs (and that there weren't more enemy moving towards Plymouth) or you might have lost that PAR.
Next time wait until YOU WON THE BATTLE before flying in the PAR. Now it can happen that new enemy reaches Plymouth after 1st battle is won but just before PAR arrives - and you will get same that seems to have possibly happened to you. That is bad luck, or poor timing, or just slow to get the PAR airborne.
HOWEVER, there is a crucial check you make the hour before your guys jump out of the plane. You assure Plymouth is still empty (retreaters don't matter). Because - if not - you can cancel the airborne drop as long as it has not yet reached over Plymouth. NEVER jump a PAR onto ongoing battle unless you certain no enemy can be moving to reinforce defense. Or only do it if indeed you know what you are doing, have the power, and purposefully want to destroy everything the enemy can throw at you in one single battle.
Play it at very slow speed if you must. But cancelling airdrop is no problem. Plane returns to base, and paratroopers remain aboard so your TRA is not zero-orged.
Better luck next time!
And I guess that your next fright might be when a single PAR is alone in Plymouth; and he actually is being attacked by many units, and the enemy red combat bar is near its maximum while you have no TPs nearby. DON'T PANIC. That PAR can survive far more than you probably might imagine - if you remembered to add OS. But I don't see OS on the PAR you show... and that can be a serious mistake because your PAR is on just 10% ESE. So - if he had to defend alone - he would not last as long as is possible if you go in prepared.
