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

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

Battle of the Atlantic: Archaeology of an Underwater WWII Battlefield: Mission Logs: September 4: NOAA Office of Ocean Exploration and Research

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

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

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

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The Forgotten Surrender: World War I and the German U-boat fleet, by Rebecca Jane Morgan

U-boat - Wikipedia

The Jones Act: A Burden America Can No Longer Bear

Wreckage of cargo ship sunk by German U-boat in WWI found at bottom of Irish Sea - Mirror Online

20 Facts About the Battle of the Atlantic in World War Two

10 Fascinating Facts About the First Battle of the Atlantic

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

US Navy destroys boats controlled by Iran-backed militias in Red Sea