Aged 28 years old, Uboat SM UB-55 was commanded by Oberleutnant Z Ralph Wenninger, UB-55 added to the U-Flottile Flandern in August 1917. She left Zeebrugge on her final patrol on 21st April 1918 with 35 men, 28 crew and 7 trainees. In the early hours, she reached the Dover Barrage, diving to avoid searchlights. Shortly after leaving the surface, an explosion occurred on her starboard side between the engine room and stern. Two compartments flooded immediately, the submarine coming to rest some 33 metres on a sandy seabed.
One of her engineers tried to shut the watertight door between the engine room and torpedo room, but it was impossible. Every time he tried to close the door, the flooding water forced it back, water jetting into the compartment whilst the men were thrown to their feet.
As the starboard ballast tanks were ruptured, Wenninger could not bring his vessel to the surface. The crew in the stern sections and engine room had already drowned, while the survivors huddled near the hatches on the middle and foreward. Twelve men in the forward and eight in the middle command centre.
The lights went out and the survivors were forced to use headlamps and while the rising water increased the internal air pressure, they experienced immense headaches. Breathing became difficult and painful while the penetration of the seawater into the battery compartments lead to the leakage of chlorine gas. Panic ensued and two crewmen tried to commit suicide using a pistol, unsuccessful as the cartridges were damp.
An hour and a half passed and the cold water had reached a height of 1 metre, making it possible to equalise the pressure to open the foreward and conning tower escape hatches. Wenninger knew that there were only four Dräger escape sets, dividing the survivors into two groups. Six men beneath the conning tower hatch and twelve men under the hatch in the torpedo room.
When the hatches were opened, most of the crew were able to escape within the enormous air bubble. However, most suffered embolisms and lung overexpansion and were found dead on the surface. There were still eight survivors found floating on the surface, one being Wenninger, picked up and saved by the British trawler Mate and one who died without gaining consciousness on the trip back to Dover. Of the others, two of the survivors were vomiting blood and oil, whilst others would not stop screaming.
The survivors were Ralph Wenninger, Friedrich Dietrich, Fritz Jahnke, Alex Neumann, Ewald Kestner and Peter Hammel. After the war, Wenninger remained in the navy and joined the Luftwaffe on 1st March 1935 and died in Italy under unknown circumstances on the 13th March 1945. Topical in today’s world of Covid-19, Dietrich died seven months later from Spanish Flu at the Shipton officers camp.