Containment is a geopolitical strategic foreign policy pursued by the United States. It is loosely related to the term cordon sanitaire which was later used to describe the geopolitical containment of the Soviet Union in the 1940s. The strategy of "containment" is best known as a Cold War foreign policy of the United States and its allies to prevent the spread of communism after the end of World War II.
Because they knew that Germans could sink any ship they want. They could sink civilian ships. Back then, the only way to travel long distances was by boat, because passenger airplanes had not been invented. The Germans could now sink them if they wanted to travel somewhere, so they either risk their life or not go on trips.
Going through the great depression
ship...and world war 1 took place from 1914-1918....just wanted to point that out