Subs Struggled, But Changed WW II for America

When the United States entered World War I, it cited among its reasons the renewed unrestricted submarine warfare practiced by the Imperial German Navy. So-called cruiser rules of the day required submarines to warn merchant ships before attacking and sinking them. After the British armed merchant vessels, the Germans decided the cruiser rules were impractical and ignored them, attacking ships without warning. Most American and British naval officers, and many of their German counterparts, considered submarine warfare inhumane, dishonorable, and outside the rules of warfare among gentlemen.