I've sailed straight into Scapa Flow (and out) submerged at ahead 1/3 ... it took me a whole day, but hey! I had at least 4 warship contacts at all times and even picked off a torpedo boat on my way out.
If you don't have the dodgey patience to wait and inch forward under water (and possbility of being DC'd with no room to dive), don't sail through the English Channel
