A graphic adventure in 4 parts from Thriller Picture Library #372, August 1961 - 64 pages. Reprinted in Secret Agent Picture Library Holiday Special 1968.
German U-boats are hiding in Irish waters in violation of that nation's neutrality. They then are able to attack convoys heading to the UK and worse yet, they know in advance which are the more precious cargos. Spy 13 is sent to learn how they know.