Some good technical stuff recently on the thread. The only thing I would disagree with is Fischerking's comment on U Boat speeds. I would have said that our vessels were a similar speed to a surfaced U Boat - about 15/16 knots. moreover a surfaced U Boat's speed is probably more affected by the sea state. If the sea is rough, their low freeboard would mean that full speed might mean the conning tower being swamped.

as for detection - we have 2 tricks up our sleeve - aircraft (from gib in this instance) and Enigma code messages