Garrison
Donor
Vegitarian I think is far more insidious, it can cripple the countrys food supply and of course spread Anthrax amongst citizens. Its a slow bake but effective and utterly ghastly method.
Plus it's not going to be an either/or choice. Though I suspect gas may be less effective against Germany than Japan simply because they've already dispersed their industries to counter strategic bombing, which means the workers have also been dispersed.