The correct answer to this open question is the following.
What is true about Germany's use of U-boats is that these boats sank ships that carried civilians during World War 1, such as the RMS Lusitania ship.
A German U-boat sank the RMS Lusitania transatlantic ship that transported civilians on May 7, 1915. Great Britain had declared the North Sea as a war zone in 1914 and prohibited all imports coming from Germany. Although the Germany embassy in the US published in the newspaper warnings to avoid navigation in the conflictive zone, the Lusitania navigated those waters and the tragedy occurred. This was one of the reasons that pushed President Woodrow Wilson into Worl War 1.