On this day, 84 years ago, September 4, 1941 (July 13, 1941 in the lunar calendar), the "Greer" incident occurred. On September 4, 1941, the Greer incident occurred. While carrying out an escort mission in the waters southeast of Iceland, the U.S. destroyer Greer came into contact with the German submarine U-652 and guided British patrol aircraft to drop depth charges. The German submarine fired a torpedo at the Greer but failed to hit it. The Greer immediately dropped a depth charge on the German submarine and injured U-652. As a result, the Greer became the first U.S. warship to fire on a German submarine. On September 11, President Roosevelt issued a statement on the "Greer" incident, announcing that as long as Axis submarines entered the waters that must be protected by U.S. defense, they would attack them immediately without warning if discovered. The strength of the United States began to emerge