Interesting related note about Brest (which I bet you know, but throwing it in for the benefit of the thread): in WW2, once our anti-submarine capability got up to speed, transiting the continental shelf to or from Brest was one of the most dangerous times for a u-boat. Diesel subs were really only mobile on the surface, and were easily spotted from the air. Over the shallow continental shelf there wasn’t enough depth to escape once spotted.