Nazi U-652 vs. U.S.S. Greer:
Wikipedia: Germany claimed "that the attack had not been initiated by the German submarine; on the contrary... the submarine had been attacked with depth bombs, pursued continuously in the German blockade zone, and assailed by depth bombs until midnight." The communique implied that the U.S. destroyer had dropped the first depth bombs. Germany accused President Roosevelt of "endeavoring with all the means at his disposal to provoke incidents for the purpose of baiting the American people into the war."
The United States Department of the Navy replied that the German claims were inaccurate and that "the initial attack in the engagement was made by the submarine on the Greer." Roosevelt made the Greer incident the principal focus of one of his famed "fireside chats", where he explained a new order he issued as commander-in-chief that escalated America nearer to outright involvement in the European war. In Roosevelt's words:
The Greer was flying the American flag. Her identity as an American ship was unmistakable. She was then and there attacked by a submarine. Germany admits that it was a German submarine. The submarine deliberately fired a torpedo at the Greer, followed by another torpedo attack. In spite of what Hitler's propaganda bureau has invented, and in spite of what any American obstructionist organization may prefer to believe, I tell you the blunt fact that the German submarine fired first upon this American destroyer without warning, and with the deliberate design to sink her.
Declaring that Germany had been guilty of "an act of piracy," President Roosevelt announced what became known as his "shoot-on-sight" order: that Nazi submarines' "very presence in any waters which America deems vital to its defense constitutes an attack. In the waters which we deem necessary for our defense, American naval vessels and American planes will no longer wait until Axis submarines lurking under the water, or Axis raiders on the surface of the sea, strike their deadly blow—first." He concluded:
The aggression is not ours. [Our concern] is solely defense. But let this warning be clear. From now on, if German or Italian vessels of war enter the waters, the protection of which is necessary for American defense, they do so at their own peril. . . . The sole responsibility rests upon Germany. There will be no shooting unless Germany continues to seek it.
Senator David I. Walsh (Democrat–Massachusetts), isolationist Chair of the Senate Committee on Naval Affairs, scheduled a committee hearing to unearth the details of the incident, which prompted Admiral Harold R. Stark, Chief of Naval Operations, to issue a written report. Stark's account, made public in October 1941, confirmed that the Greer dropped its charges only after the submarine fired its first torpedo at it, but revealed that the Greer had gone in search of the submarine after its presence was noted by the British aircraft. Admiral Stark's report stated:
At 0840 that morning, Greer, carrying mail and passengers to Iceland, "was informed by a British plane of the presence of a submerged submarine about 10 miles [(16 km)] directly ahead. . . . Acting on the information from the British plane the Greer proceeded to search for the submarine and at 0920 she located the submarine directly ahead by her underwater sound equipment. The Greer proceeded then to trail the submarine and broadcasted the submarine's position. This action, taken by the Greer, was in accordance with her orders, that is, to give out information but not to attack." The British plane continued in the vicinity of the submarine until 1032, but prior to her departure the plane dropped four depth charges in the vicinity of the submarine. The Greer maintained [its] contact until about 1248. During this period (three hours 28 minutes),the Greer maneuvered so as to keep the submarine ahead. At 1240 the submarine changed course and closed the Greer. At 1245 an impulse bubble (indicating the discharge of a torpedo by the submarine) was sighted close aboard the Greer. At 1249 a torpedo track was sighted crossing the wake of the ship from starboard to port, distant about 100 yards [(100 m)] astern. At this time the Greer lost sound contact with the submarine. At 1300 the Greer started searching for the submarine and at 1512 . . . the Greer made underwater contact with a submarine. The Greer attacked immediately with depth charges.
Stark went on to report that the result of the encounter was undetermined, although most assumed from the German response that the sub had survived.
Prominent historian (and isolationist) Charles A. Beard would later write that Admiral Stark's report to the Senate Committee "made the President's statement... appear in some respects inadequate, and, in others, incorrect." In his postwar summary of the Stark report, Beard emphasized that (1) the Greer had chased the sub and held contact with the sub for 3 hours and 28 minutes before the sub fired its first torpedo; (2) the Greer then lost contact with the sub, searched, and after re-establishing contact two hours later, attacked immediately with depth charges, then (3) searched for three more hours before proceeding to its destination.
The Stark report's account of how the Greer's engagement began caused Pulitzer-prizewinning New York Times reporter Arthur Krock to address it (and the Nazi sub engagements with the Kearny, and the Reuben James) when speaking about "who 'attacked' whom." Krock defined the term "attack" as "an onset, an aggressive initiation of combat, a move which is the antithesis of 'defense.'" "In that definition," he said, "all three of our destroyers attacked the German submarines."