depends on japan setup.
do not use usa dd to block for india or new south wales (japan can declare war on just uk / anzac and ignore usa on his attacks).
I do use usa dd to block for some dutch islands sometimes. Like say Japan sets up in carolines… I keep usa dd right where it is to block japan from isles. I use uk pac dd and anzac dd to block the other lanes. I take java and sumatra.
Why do I block? sure -24 for me but not +8 for japan and get to bank 8 more next turn for uk pac and anzac… at the same time it sets japan back… now japs got to take more islands the next round and try to defend each location.
Really depends though. sometimes I bring it strait down or I bring it toward uk pac or I bring it toward anzac.
Depends on how many battles I want to line up for Japan on his next turn.
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Fighting Japan works like this, you either A) move all the allies in at the same time so Japan can’t fight everything. B) you don’t give him any big battles.