More U-boats were sunk, but the number operational had more than tripled.[91] After the improved radar came into action shipping losses plummeted, reaching a level significantly (p=0.99) below the early months of the war. The development of the improved radar by the Allies began in 1940, before the United States entered the war, when Henry Tizard and A. V. Hill won permission to share British secret research with the Americans, including bringing them a cavity magnetron, which generates the needed high-frequency radio waves.[92] All sides will agree with Hastings that "... mobilization of the best civilian brains, and their integration into the war effort at the highest levels, was an outstanding British success story."[93]