Final answer:
The defenselessness of merchant and passenger ships against U-boat attacks in WWI stemmed from a lack of initial countermeasures and U-boats' stealth tactics, which violated international law. Only with American naval escorts' help and the establishment of the convoy system were the Allies able to reduce shipping losses.
Step-by-step explanation:
During World War I, passenger and merchant ships were largely defenseless against German U-boat attacks because the Allies initially lacked effective countermeasures. This vulnerability persisted until the introduction of American naval escorts and the convoy system in 1917, which then mitigated the U-boat threat. The Germans declared waters around Great Britain a war zone and, unlike traditional naval warfare, U-boats attacked without warning from beneath the surface, breaching international law. These submarines, originally surfacing before attacking, changed tactics after the German U-boats were targeted by armed merchant vessels.Convoys and naval escorts significantly decreased losses by protecting civilian craft from submarine attacks. Additionally, the rapid development of American naval escorts played a crucial role in safeguarding transatlantic supply routes, which was pivotal as the American army began arriving in Europe.Conclusion The advent of U-boat warfare represented a harsh departure from traditional naval standards and caught the Allies unprepared, leading to significant shipping losses until effective counter-tactics were adopted.