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

U-boat - Wikipedia

The Ghosts Who Haunt the South China Sea - The Atlantic

A Massive Operation - Raising A U-Boat To Recover Her Precious Cargo

Red Sea conflict: Dozens of Canadian ships delayed

The Times archive of First World War articles

How to end a filibuster: World War I and the origin of the cloture rule

The Deadliest Disaster at Sea Killed Thousands, Yet Its Story Is Little-Known. Why?, History

U-boat, German Submarine Warfare in WWI & WWII

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