1st of 2 graphic adventures from Thriller Picture Library #336, October 1960 - 32 pages.
The year is 1940 and already Spy 13 has been on many dangerous and tough assignments. His boss feels he needs a short rest before the next big case so David Doughty heads to the east coast of England for a breather. Doing some night swimming turns eventful when he is literally bumped into by a U-boat! Things get very interesting after that!