4 Sep, 1941
On 4 September 1941, USS Greer had been signaled by a British bomber, that a German submarine was hiding in the vicinity. Greer found sound contact, and started to pursue the U-boat U-652 from close range. The aircraft dropped 4 depth charges, and left the scene, leaving the two fighting ships. Soon after the U-boat fired a torpedo at the US warship, perhaps believing she dropped the four bombs. After this USS Greer went into attack, and a 2 hour battle followed, during which she dropped 19 depth charges, and the U-boat fired another torpedo, without results. President Roosevelt used this event in his campaign to convince the US to go to war, and the "undeclared war" between U-boats and US escorts escaleted dramatically.

1 Mar, 1942
USS Greer picks up 13 survivors from the Panamanian merchant Equipoise thaty was torpedoed and sunk on 27 February 1942 about 60 miles south-east of Cape Henry in position 36º36'N, 74º45'W by the German submarine U-160.

23 Apr, 1942
USS Greer picks up 24 survivors from the American merchant Robin Hood that was torpedoed and sunk on 16 April 1942 by the German submarine U-575 about 300 nautical miles south-east of Nantucket Island, Massachusetts in position 38º45'N, 66º45'W.