Why was the German use of the unterseeboot considered to defy international law?

because other countries did not have similar technology

because they refused to warn their targets before firing

because they constituted cruel and unusual methods

because no international consensus existed to employ submarine technology

The correct answer is B. Because they refused to warn their targets before firing

Explanation:

During the First and Second World War, the military forces of German widely used Unterseeboots or U-boat that were submarines to attack enemy ships this included not only military targets but also merchant ships and passenger ships. However, as by using these submarines Germans could destroy any boat or ship without the passengers and civilians to surrender or scape its use become quite controversial especially as international laws established attacking without warning was against the law and instead the submarines needed to go to the surface and allow people in ships to surrender if they wanted and in this way avoid the death of civilians or crew as they were not directly involved in the war. This led to the Sussex pledge in 1917 in which Germany promise to avoid atacking passenger ships and warning other ships before atacking, but this was not completely followed by Germany as the actions of U-boats continue. Therefore, the reason German use of the U-boats defy international law was because they refused to warn their targets before firing.