1917, the fourth year of the Great War, saw another year in the trenches for millions of troops mobilised in Europe. Apart from short patrols in the North Sea, the ships of the Royal Navy and Germany's imperial navy remained in port. However, the enemy submarines were in operation intensively. In March, three American ships were sunk in one day, finally bringing the United States to the brink of war. President Woodrow Wilson made an impassioned speech...