Roosevelt publicly confirmed the "shoot on sight" order on 11 September 1941, effectively declaring naval war against Germany and Italy in the Battle of the Atlantic.

Greer's shake down took her to Azores, from which she rendezvoused with George Washington, carrying President Woodrow Wilson home from the Versailles Peace Conference, and escorted her to the United States.

After exercises in coastal waters, Greer was assigned to Trepassey Bay, Newfoundland, for duties during a transatlantic flight by four Navy seaplanes, one of which, NC-4, safely completed the historic undertaking.

After further training exercises and a European cruise, Greer was assigned to the Pacific Fleet, reaching San Francisco 18 November 1919.

After standing by off Shanghai to protect American lives and property during riots there in May, Greer sailed to Port Arthur and Dairen on intelligence missions and returned to Cavite, Philippines, for fleet exercises.

Training exercises, battle practice, and plane guard duty filled Greer's peacetime routine for the next 2 years.

After conducting Naval Reserve cruises throughout that summer, Greer sailed for the Philadelphia Navy Yard 28 September and decommissioned there 13 January 1937.

[2] 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.

"[3] 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.

"[4] 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.

[5]Declaring that Germany had been guilty of "an act of piracy,"[5] 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.

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.

In fact, U-652 had indeed survived and promptly headed west to participate in the devastating U-boat pack attack on convoy SC 42 in early September.

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.

"[9] A 2005 book concluded that Senator Walsh's "very aggressive actions in the USS Greer case prevented war from breaking out in the Atlantic.

Hitler concentrated his resources on defeating the Soviet Union, while Roosevelt was building up a broad base of support for aggressive patrols of the North Atlantic.

[12] Greer remained in the North Atlantic through 1941, shepherding convoys to and from MOMP, the mid-ocean meeting point at which American ships took over escort duties from the hard-pressed Royal Navy.

During heavy North Atlantic gales, Convoy SC 121 lost seven ships to three separate U-boat attacks before reaching Londonderry Port on 13 March.

Her name was stricken from the Navy list 13 August and her hull was sold to the Boston Metal Salvage Company of Baltimore, Maryland on 30 November 1945.