WW1 Submarines: The U-Boat Threat
German submarines—U-boats (Unterseeboote)—nearly won the war for Germany. They also brought America into the conflict.
Learn more in our World War 1 Guide →
Why Submarines Mattered
- Island nation
- Dependent on imports
- Food, weapons, raw materials came by sea
- Cut off supplies = defeat
- Surface fleet couldn't defeat Royal Navy
- U-boats could strike shipping
- Starve Britain into submission
The U-Boat Campaign
Early Restrictions
- Limited submarine warfare
- Warning ships before sinking
- Following prize rules
- Relatively few sinkings
Escalation
- British liner sunk without warning
- 1,198 dead including 128 Americans
- Outrage nearly brought US into war
- Germany temporarily backed down
Unrestricted Submarine Warfare
- No warnings
- Neutrals included
- Maximum destruction
The calculation:
Germany believed it could starve Britain before America could mobilize.
- April 1917: 860,000 tons sunk
- Britain had only six weeks of grain
- But US declared war
U-Boat Technology
- Limited range
- Slow underwater
- Vulnerable when surfaced
- Crew: 30-40
- Spent most time surfaced (faster, batteries charged)
- Diving was for attack or escape
- Primitive sensors
- Cramped, dangerous conditions
- Torpedoes (expensive, limited supply)
- Deck guns (for smaller vessels)
Allied Counter-Measures
Convoy System
- Ships traveled in groups
- Escorted by warships
- Much harder for U-boats to attack
- Dramatically reduced losses
- Hard to find convoys in vast ocean
- U-boats couldn't attack escorts
- Made submarine hunting easier
Other Measures
- Depth charges — Bombs that exploded underwater
- Hydrophones — Primitive sonar
- Q-ships — Armed ships disguised as merchants
- Mine barriers
The Numbers
- 360 U-boats built
- 5,000 ships sunk
- 200 U-boats lost
- 5,000 German sailors died
- 12 million tons of shipping
- 15,000 merchant sailors died
- Almost succeeded in defeating Britain
Legacy
- Proved submarines as strategic weapons
- Led to convoy tactics
- Influenced international law
- Set stage for WW2 Battle of the Atlantic