DUH: How to quickly regain sonar contact on a U-boat
Battle of the Atlantic Volume 4 Technical Intelligence From Allied Communications Intelligence
USS Piper (SS-409) during WW2 (top) and in 1968 (bottom) after multiple refits to add a snorkel and a new bow sonar as well as streamline the boat. : r/submarines
German U-boat may be at bottom of Labrador river | CBC News
UC47: Horrors of submarine warfare in WWI revealed using new technology | The Independent | The Independent
The Radio Crew - The U-boat Crew - The Men of the Kriegsmarine - uboat.net