29 August 1918
Sinking of UB-109
Sinking of UB-109
A sonar mosaic of the UB-109 wreck, from 2014.
The Dover Barrage, designed to stop German submarines from passing through the Straits of Dover on their way to the English Channel or the North Atlantic, had grown increasingly sophisticated by the final months of the war. In addition to anti-submarine trawlers and contact mines at a variety of depths, the barrage now had sophisticated means of detecting submarines, and operators on shore who could detonate mines remotely once submarines were detected. These means included hydrophones, picking up any sounds made by the submarines, and large “Bragg loops” of wire, which would detect the large amount of metal in a submarine by induction (similarly to how many intersections with traffic lights detect the presence of a waiting car).
The German submarine UB-109 had left Zeebrugge a month earlier (the blockships sunk there by the British no longer being an obstacle) for a mission to the Azores, and decided to return via the Straits of Dover. There, they were detected by a hydrophone, and then by a Bragg loop seventeen minutes later. At 4:20 AM, the operator on shore then detonated one to four mines in the vicinity. The explosion broke the submarine nearly in two, and it quickly sunk to the sea floor. Many of those in the vicinity of the conning tower survived the initial blast (although they suffered ear damage from the sudden rise in air pressure) and were able to escape, as the water was not too deep. Eight survivors were picked up by an anti-submarine trawler soon after.
A sunken U-boat in shallow water provided a great opportunity for the Royal Navy. Within a day, a team of divers called the “Tin Openers” had found the wreck and began exploring it, hoping to find documents with intelligence value, or at the very least more information about the working of German U-boats.
Photo and text credit today-in-wwi.tumblr.com
It's interesting to see how sophisticated British anti-submarine defences had become. But surely the Germans should have known by 1918 that the Dover Straits were impassable.
Among the survivors was Kapitänleutnant Kurt Ramien, commander of the submarine.
Kapitänleutnant Kurt Ramien - German and Austrian U-boats of World War One - Kaiserliche Marine - uboat.net