Two First World War submarine attempts illustrate different stages of harbour defence. U-18 was forced to surface after a trawler rammed it in 1914, showing how patrol craft could compensate for an immature fixed-defence system. By October 1918, UB-116 encountered working hydrophones and shore-triggered mines before it could enter the anchorage. Secure anchorage depended on patrols, detection, obstacles, and controlled weapons working in layers. The remotely triggered destruction of UB-116 also prompts a comparison with modern drone warfare: remote killing has a long history, even if its present scale is new.
Chapter · 24:04-25:53
Submarine attacks test Scapa Flow's defences
The failed U-18 and UB-116 incursions show how harbour defence evolved from chance contact to hydrophones and controlled mines.