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World War I: Understanding the War at Sea Through Maps

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(The following guest post is by Ryan Moore, a cartographic specialist in the Geography and Map Division.)

Sperrgebiete um Europa und Afrika. 1925. Geography and Map Division.
Sperrgebiete um Europa und Afrika. 1925. Geography and Map Division.

Soldiers leaping from trenches and charging into an apocalyptic no man’s land dominate the imagination when it comes to World War I. However, an equally dangerous and strategically critical war at sea was waged between the Central Powers and the Allies, with Germany and Great Britain as the primary belligerents. The primary strategy was to disrupt the flow of supplies, thereby diminishing the other side’s ability to fight.

In 1914, the Allies commenced a blockade, which included the draconian measure of declaring food as contraband of war. Germany responded with one of its own, using its submarine fleet, known as U-boats, to sink merchant ships. The map “Sperrgebiete um Europa und Afrika” (“Restricted zones Europe and Africa”) depicts areas where Germany threatened to sink both Allied and neutral merchant ships.

Although Germany publicized its plan, the strategy ran contrary to the accepted rules of war. The practice prior to attacking a merchant ship was to fire a warning shot; inspect the ship for contraband of war, and if found, evacuate the crew and passengers, providing them with safe refuge; or finally sink or capture the ship. This method was impractical for small submarines, which could not accommodate additional persons aboard. But more so, it sacrificed the submarine’s surprise attack potential. After weighing their options, the Germans proceeded with a shoot without warning policy that became known as “unrestricted submarine warfare.”

American civilians were soon after caught in the crossfire. On May 7, 1915, the passenger ship RMS Lusitania was torpedoed and sunk off of Ireland by a U-boat, and of the 1,959 people on board 1,198 died, including 128 Americans. President Woodrow Wilson was outraged, because he believed that Americans had the right to “Freedom of the Seas” and should be able to travel safely on any civilian ship despite the war. He demanded that the Germans conform to the rules of war. American newspapers explained the issue with maps that illustrated areas where Germans submarines were active as well as minefields.

“British Islands: Approximate Positions of Minefields. 19th August 1918.” Hydrographic Department of the Admiralty, under superintendence of Rear-Admiral J.F. Parry, C.B. Hydrographer, August 6th, 1917. Geography and Map Division.
“British Islands: Approximate Positions of Minefields. 19th August 1918.” Hydrographic Department of the Admiralty, under superintendence of Rear-Admiral J.F. Parry, C.B. Hydrographer, August 6th, 1917. Geography and Map Division.

The Germans feared the political repercussions of their strategy and curtailed these attacks. Germany continued, however, to employ some 43,000 sea mines that claimed more than 500 merchant vessels by the end of war. The British Navy lost 44 warships and 225 auxiliaries to mines. The British, in response, constantly swept for mines that frequently threatened their naval facilities, commercial ports and ports in Ireland, which were often a stopover for ships sailing from North America. This blog post from World’s Revealed looks at these sea mines.

Britain hoped to use its superior surface fleet to destroy the German counterpart in Trafalgar-type engagement, an allusion to Admiral Horatio Nelson’s destruction of the French fleet in 1805. The opportunity came at the Battle of Jutland (May 31-June 1 1916), where the British lost 14 ships and more than 6,000 men, and the Germans lost 11 ships and more than 2,500 men. Though a German tactical victory and an utter shock to British pride, the Kaiser’s fleet never again seriously challenged British control of the North Sea and the blockade of Germany continued.

Desperation to break the deadlock in the land war and growing short of supplies, Germany resumed unrestricted submarine warfare in 1917. Attacks were planned on all commercial vessels, which included attacks on American ships, as illustrated in the map “Amerikanisches Sperrgebeit.” In response, the United States severed diplomatic relations with Germany, and the two nations were at war within months.

The U-boat attacks were devastating. The map “Die Schiffsversenkungen unserer U-Boote” (“Ships sunk by our U-boats”) highlights the carnage. By the end of the war, Germany had sunk more than 5,000 merchant ships and more than 100 warships; tens of thousands of lives were lost. This was achieved at a high cost to the German navy, as 217 of its 351 submarines were sunk with a loss of more than 5,000 sailors. The German effort, nonetheless, could not overcome Allied sea power and their industrial capacity to replace lost ships and supplies.

More information on the Library’s World War I maps can be found in this guide.

World War I Centennial, 2017-2018: With the most comprehensive collection of multi-format World War I holdings in the nation, the Library of Congress is a unique resource for primary source materials, education plans, public programs and on-site visitor experiences about The Great War including exhibits, symposia and book talks.


  1. Barbarous and brutal on land and sea. Imperial attitudes led/lead to destructive and costly wars. Fueled by attitudes of property and resource ownership led to aggression, ethnic superiority and religious zeal, ending lives, and destroying cultures.
    Lines and colors on paper, flags and declarations do tell the story.
    Thank you.

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