Neat link! Thanks for that one.
So, it is important to remember that submarines of WWI were drastically less capable and sophisticated than the ones we think of from WWII. Don't forget, the first practical dual-drive submarine had only been perfected around 1900. In addtion to being slower and possessed of less endurance, WWI subs were also hampered by their armament. The torpedos of the time were slower, shorter ranged, less mechanically reliable, and were equiped with smaller warheads.
All that being said, naval archetects of the time were astonishingly bad at designing ships capable of standing up to catastrophic underwater damage. As a result, even a single mine or torpedo hit could be deadly to even the largest of dreadnoughts, as seen with the HMS Audacious. The Audacious was a top-of-the-line battleship, barely two years old when a single mine hit
sent her to the bottom. Given this demonstrated vulnerability, naval commanders had to take the threat posed by the relatively primative submarines of the time seriously.
On top of that, at the start of the war there was no effective ASW weapons available, short of raming the offending submarine while it was at periscope depth or luring it in on the surface to attack what appeared to be a harmless merchant, but which was in fact a heavily armed "Q-ship." Effective depth charges weren't available before 1916, and no SONAR systems (other than primitive listening gear) existed until well after the war. Thus, submarines enjoyed a certain impunity from counter-attack at the outset that helped offset their other limitations.
