may 8, 1945 - Battle of the Atlantic
German U boats continued to sink the allied boats until the US started using Radar and Sonar. Radar detected U-Boats above the water and Sonar could detect U-boats underwater before they could attack. By 1943, Allies were building more ships than Germany could sink and destroying more U-boats than Germany could build. This was significant because the Battle of the Atlantic continued throughout the whole war.
Added to timeline:
Major Events of WWII