..and the amount of propaganda leverage the USA and Britain made of it. It is actually hard to determine fact from fiction, regarding the U boat campaign of the 1st WW. IMO.But everybody had developed the technology. Arguably, the Germans did not have the most technologically advanced submarines. What made them significant was the way they were used.
The infamous sinking of the civilian ship, the Lusitania (1915) was one such event. A civilian passenger ship carrying an estimated 173 tons of military munitions etc...claimed to be a Neutral civilian passenger liner... etc etc...