When the U boats were unleashed on the world's shipping

U-BOATS UNLEASHED ON EAST COAST SHIPPING - World War II Day by Day

Sea Wolves Unleashed – Inside Germany's First U-Boat War

Reviews for The Caribbean War Front in World War II: The Untold Story of U- Boats, Spies, and Economic Warfare — Markus Wiener Publishers

The Key Role of the Convoys Naval History Magazine - August 2020 Volume 34, Number 4

Rising tide: Submarines and the future of undersea warfare

Red Sea conflict: Dozens of Canadian ships delayed

The Battle That Had to Be Won Naval History Magazine - June 2008 Volume 22, Number 3

The WW1 Q-Ships Were Heavily-Armed Decoy Vessels, Designed To Lure Unsuspecting U-Boats Into A Trap

The Shipping Industry's Transition To Atomic Power And Faster Deliveries

Did the design and propulsion of the German Navy's Type XXI U Boat influence post World War Two submarine design? - Quora

How German U-Boats Were Used in WWI—And Perfected in WWII

UK Researchers Find Wreck of a Steamship Sunk by U-Boat in WWI

K-Ships vs. U-Boats National Air and Space Museum

Could the German U Boat Type XXI have decisively altered the course of the Second World War at sea if they had been available in greater numbers? - Quora