On this day in 1940, the American destroyer Greer becomes the first U.S. vessel fired on in the war when a German sub aims a few torpedoes at it, sparking heightened tensions between Germany and the United States.
It was a case of mistaken identity. As the Greer made its way through the North Atlantic, a British patrol bomber spotted a German sub, the U-652. The British bomber alerted the Greer, which responded by tracking the sub. As the American destroyer approached Iceland, the area in which the sub had been spotted, a British aircraft dropped a depth charge into the water, rocking the sub. The U-652, believing the Greer responsible for the charge, fired its torpedoes. They missed. The Greer made it safely to Iceland. Although the United States was still officially a neutral country, Roosevelt unofficially declared war on anyone who further attacked American vessels in the North Atlantic: "If German or Italian vessels of war enter these waters, they do so at their own peril."