The Germans have no destroyer present, therefore the defending air units can not hit the sub, and of course the sub can never hit planes. Think of it in terms of the combined arms rule, air units can only hit subs if they are combined with at least 1 participating destroyer, the difference with this particular combined arms is that it works while attacking and defending. In the scenario that you described, the sub would destroy the remaining transport without rolling and the defending fighters can do nothing.
Japan and Russian war state question
I was wondering if Japan declares war to russia in J1 does it gives UK/Anzac right to do a PROVOKED declaration fo war against Japan?
The answer is really important as it means japan could then be at war with UK/Anzac, Take fic and take the dutch islands while the US cannot declare war on japan because UK did provoke the war in that sense US still can’t enter in war because japan did not provocate as stated in the rules?
Of course G1 did not war on russia in that case.
Japan/Russia has no effect on UK/Anzac relations to Japan.
UK/Anzac can declare war on Japan “when they want” (so to speak)