The best example I can think of is Lombok Strait, where subs transiting between Fremantle and their patrol areas had to - IIRC - fight the current going to station but could drift with it coming off station. Its speed varied but I think it was about 6 knots. That, I think, is one of the fastest currents the boats had to deal with. Seems like I read about one boat making about 1 knot forward speed through there. I'll dig around and see if I can find the specifics.
