what aim does this german-sub-strat include? i am not clear about your intentions, so i ask.
i also was thinking about a german preparation with lots of subs just for stalling the american approach towards europe. which means, in G5 you should be ready and in the position to attack an american navy right before gibraltar. this very navy can get there in earliest at USA4.
and this means that you´ll have to fight probably a fleet consisting of the destroyer and transport of the beginning and 105 IPC additional buys. i guess minimum one carrier fully loaded, maybe cruisers or a battleship, for sure more destroyers, transports, subs as cannon-fodder.
without any landing zone for german aircrafts, this is going to be suicidal. but with 10+ subs and minimum 3 strategic bombers there could be inflicted serious damage. but this means you´ve spended some 100IPC only in naval buys, which means russia is safe!
well, for me this strat is not working. the US cannot effectively delayed, can it?