On this day in 1917, Germany announced the renewal of unlimited submarine warfare in the Atlantic. German torpedo-armed submarines prepared to attack any and all ships, including civilian passenger carriers, said to be sited in war-zone waters.

Spiraling Events. Within three days, the US severed all diplomatic ties with Germany. Hours later, the American liner Housatonic was sunk by a German U-boat. None of the 25 Americans on board were killed; they were all eventually picked up by a British steamer.

Subs. What Are They Good For? And How Good Are They? Before World War I, submarines were not considered an effective tool for blockading an enemy country. Submarines, filled with pipes and machinery, had no room for prisoners. They couldn't carry enough sailors to provide crews to man captured ships. The Germans had an answer to that ~ unrestricted submarine warfare. Instead of capturing a merchant ship, they could just sink it ~ crew and all.

A Background of History...

War Begins. US Doesn't. In 1914, when World War I broke out, President Woodrow Wilson pledged neutrality for the United States. This was a position endorsed by most US citizens. The US and Britain were close trading partners, however. So when Germany attempted to cut off the British Isles, the situation between the US and Germany became tense.

Free-for-All. In February of 1915, Germany announced unrestricted warfare against all ships that entered the war zone around Britain. It did not matter if those ships were neutral or enemy ships.

Making Good on Their Word. A month later, Germany announced that one of their cruisers had sunk the William P. Frye, a private American ship that was transporting grain to England. President Wilson was outraged. The Germans apologized, saying the attack was a mistake.

Stealth Boat. The Germans' most powerful weapon at sea was the U-boat, For the times, the U-Boat was an extremely sophisticated submarine.

U-Boat Portrait. A typical U-boat was 214 feet long, carried 35 men and 12 torpedoes, and could travel underwater for two hours at a time. For the first few years of World War I, the U-boats were extremely effective in destroying Allied ships.

Early Warning System. In May of 1915, several New York newspapers published a warning from the German embassy in Washington: Americans traveling on British or Allied ships in war zones did so at their own risk.

Ironic Placement? The announcement ran side-by-side with an ad for the British-owned Lusitania ocean liner, which was scheduled to sail from New York to Liverpool.

More Than a Warning Shot. On May 7, the Lusitania was torpedoed without warning just off the coast of Ireland. (See Today Only for May 7). More than 1,100 passengers and crew perished; over 100 US citizens were among the dead. The sinking of the ship encouraged the US to enter into World War I.

German Rationale. The German government insisted that the Lusitania was carrying ammunition, and was thus fair game. The US demanded reparations and an end to attacks on unarmed passenger and merchant ships.

Broken Promises. In August, Germany pledged to respect passenger safety before sinking unarmed vessels. It was an empty promise. In November, without warning, the Germans sunk an Italian liner, killing 272 people, including 27 Americans. This also helped turn the tide of public opinion against Germany.