Very interesting. I have heard the Dardanelles strait as a limitation before but never understood it. Maybe our group does not use it much, but what is the implication of closing it VS not?
The above “Chicago Rules” closing is a modified version of “Closing the Dardenelles Straight”, in the sense that Sea Zone 16 is still open, and you can reach Bulgaria, but not Ukraine and/or the Caucasus.
Implications are to keep yet another front from easily being opened against Russia. The axis can empty Africa via the Med fleet (German transport, Italian Navy) and give Russia even more headaches, especially early if Germany went on a strong Barbarossa game plan.