When and where did the German announce they would sink any ship found near Britain's coast?

The German announcement to sink any ship found near Britain's coast was made on January 31, 1917. This declaration marked the resumption of unrestricted submarine warfare during World War I, with Germany targeting vessels in the waters surrounding the British Isles. The policy aimed to cut off supplies to Britain but ultimately contributed to the U.S. entering the war after several American ships were sunk.