U-Boats Bring America Into World War I

"Versenkung eines feindlichen bewaffneten Truppentransportdampfers durch deutsches U-Boot im Mittelmeer (Sinking of a hostile armed troop carrier by German submarine in the Mediterranian sea)" by Willy Stower (1917)

    "Stand by for firing a torpedo!" I called down to the control room.
     "FIRE!"
     A slight tremor went through the boat - the torpedo had gone.
     The death-bringing shot was a true one, and the torpedo ran towards the doomed ship at high speed. I could follow its course exactly by the light streak of bubbles which was left in its wake.
I saw that the bubble-track of the torpedo had been discovered on the bridge of the steamer, as frightened arms pointed towards the water and the captain put his hands in front of his eyes and waited resignedly. Then a frightful explosion followed, and we were all thrown against one another by the concussion, and then, like Vulcan, huge and majestic, a column of water two hundred metres high and fifty metres broad, terrible in its beauty and power, shot up to the heavens."
-- U-boat commander Adolf K.G.E. von Spiegel, U-boat 202 (1919)

On January 31, 1917, Imperial Germany -- for 2-1/2 years engaged in a horrifyingly destructive war with Britain, France, and other Allied nations -- declared that it would pursue unrestricted submarine warfare in the North Atlantic. The Kaiser and his general staff had given up hope that the United States would come into the Great War raging in Europe on its side, or indeed that the US would even remain neutral. After two years of American shipping and lives being lost as (what we would call now) collateral damage, the stage was set for all-out war and, in May of that year, the United States did indeed declare war on Germany.

Originally envisioned as a weapon against surface warships, the U-boats (from the German Unterseeboot), proved most effective against merchant shipping. Sinking cargo ships in convoy -- from Canada and other parts of the British Empire – was not only safer for a U-boat than confronting an armed naval ship, it was ultimately more damaging to the Allied war effort.

Although at first the German Empire observed the Victorian era “rules of war” regarding neutral shipping, in early 1915 it stepped up its pressure on Britain in reaction to British mining and blockades. Any vessel sailing into or out of Britain was now considered fair game, whatever its flag. On May 7, 1915 a German U-boat sank the ocean liner RMS Lusitania, killing nearly 1200, including 128 American civilians. The sinking was a mistake; the captain of the U-20 had mistaken the Lusitania for a troopship. What was not known at the time was that the ship was carrying ammunition, the explosion of which was a possible cause of the sinking.

In March 1916, a U-boat sank the British ferry Sussex in the English Channel, injuring several Americans. It was this incident that began to turn American public opinion against Germany. In reaction, Germany, ceased all-out submarine war for several months. Unfortunately, this also reduced the effectiveness of the U-boat fleet. Finally, in October 1916, Germany decided to intensify its submarine warfare in the hopes of forcing Britain to sue for peace before the US could enter the war.

The gamble failed. Following the sinking of three US-flagged merchant ships in March 1917, the US declared war on Germany. To counteract the U-boat threat, warships began escorting the convoys, thus removing one of the main advantages of “commerce raiding.” When he war ended in November 1918, Germany had lost half its 360 u-boats, which in turn had sunk more than 11 million tons of shipping over the course of the war.

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uboat.net: His Imperial German Majesty's U-boats in World War I

EyeWitness to History.com: U-boat Attack, 1916