The scenario estimates Shanghai at roughly 1,500 kilometres from Hong Kong and treats it as a useful forward position for a war against Japan. The older Singapore Strategy supplies the campaign logic: attack the merchant shipping on which Japan's war effort depends. A China Station submarine flotilla of roughly fourteen boats provides one tool, although a couple may be under refit at Singapore. Town-class cruisers can attack trade farther afield while County-class ships and other units protect Birmingham or exploit contact with Akagi. Birmingham's safer escape avoids the Taiwan Strait, runs south along the Chinese coast into the South China Sea, and aims for Singapore while cruisers leave Hong Kong to assist. The campaign would depend on bases and patrol routes that let submarines and cruisers cover different parts of Japanese trade.
Chapter · 37:18-43:10
Commerce war with submarines and cruisers
Shanghai's position, China Station submarines, and dispersed cruisers turn a single incident into a wider campaign against Japanese merchant shipping.