Two World War I submarine attacks show the defenses evolving

U-18 entered through Hoxa Sound in November 1914 by following a steamer, but found the fleet absent because Scapa's defenses were not yet complete. A trawler damaged her periscope, a diving-plane failure sent her to the seabed, and HMS Garry rammed her before the commander scuttled the boat. By October 1918, hydrophones detected UB-116 and shore personnel detonated controlled mines, killing its entire crew. The latter attack challenges the idea that remote killing is entirely new: shore operators could detect and destroy a submarine without seeing its crew, even if modern warfare applies the principle at a different scale. The contrast shows how an exposed anchorage became a layered defense of booms, blockships, patrol craft, sensors, and shore-controlled weapons.