The impact of these changes first began to be felt in the battles during the spring of 1941. In early March, Prien in "U-47" failed to return from patrol. Two weeks later, in the battle of Convoy HX 112, the newly formed 3rd Escort Group of five destroyers and two corvettes held off the U-boat pack. "U-100" was detected by the primitive radar on the destroyer , rammed and sunk. Shortly afterwards "U-99" was also caught and sunk, its crew captured. Dönitz had lost his three leading aces: Kretschmer, Prien, and Schepke.