108 years ago today, January 31, 1917 (January 9, 1917 in the lunar calendar), Germany declared unlimited submarine warfare. On January 31, 1917, Germany announced that it would resume unrestricted submarine warfare from February 1. Regardless of the nationality of a ship, Germany will sink it with a submarine as long as it is heading towards the UK, whether it is heading for the UK or just passing through the UK. Germany hopes to kill Britain's maritime lifeline in this way. German U-boats during World War I. Each red dot represents British ships sunk by German submarines