1. A new kind of warfare
Of the 375 German submarines - U-boats - that set sail from German ports in World War One, 202 were lost in action. Most of them were destroyed by the Allies - mechanical failure and accidents accounted for others.
The German submarines terrorised Allied shipping, sinking around 2,600 vessels. Yet the sailors sent to serve in U-boats knew their chances of survival were low. Out of 17,000 men who served, more than 5,100 lost their lives.
Serving on a U-boat was one of the most dangerous occupations in the entire war.
2. Primitive machines
3. Treacherous tin can
There was no escape if something went wrong on a submerged U-boat. There was no diving gear on board if it sank to the sea bed. Even if sailors managed to overcome the water pressure and force open the hatch and get out, they almost certainly drowned.
Early U-boats were designed to protect German ports and harbours but by the start of World War One ocean-going subs had a range of 8,000 nautical miles. They could spend around five days on war patrol but only had 72 hours’ air supply. What’s more, they could only be submerged for around two hours at a time because they had to switch from diesel engines to an electric battery-powered system.
Because of the limitations of their electric batteries, U-boats tended to leave port on the surface at night and only submerged when spotted by the enemy, or after conducting an attack. Once submerged, the electric batteries posed a real threat to the crew. Johannes Speiss, a first watch officer on the U-9, recalled: “The storage battery cells, which were located under the living spaces… generated gas… ventilation failure risked explosion, a catastrophe which occurred in several German boats. If sea water got into the battery cells, poisonous chlorine gas was generated.”
4. Outgunned and outwitted
At the start of the war, U-boats employed old-fashioned rules of engagement: they surfaced, issued a warning of their attack and gave merchant crews time to escape. The main threat they faced was from being rammed by a battleship.
In response to the losses they were taking, the British changed tactics. They designed Q-ships – freighters with hidden guns – to lure out and ambush German subs. When the U-boats came to the surface to parley, the decoy ships uncovered their guns and fired at will. It was a brutally effective tactic. They sank 15 U-boats and damaged countless others.
Nowhere to hide
In 1916 the depth charge (known as the wasserbombe by the Germans) was invented and deployed.
The first confirmed U-boat to be sunk by a depth charge was the UC-19, which had sunk four Allied ships in the English Channel. In December 1916 the crew of HMS Ariel, a British destroyer, sank her 30 miles off the Belgian coast. There were no survivors.
In 1917 depth charges destroyed 12 U-boats and the following year 24. They not only wreaked havoc but also terrorised U-boat crews.
During the war U-boats were responsible for sinking a number of high profile allied ships including the Lusitania. Yet German submarines were fast becoming one of the most perilous places to be in World War One.
5. Where would you have been most in danger?
World War One was one of the bloodiest conflicts in history. But where was the most dangerous place to serve?