By the time America entered the war in December 1941, Britain had been at war with Germany for two years. Japan and Germany as strong allies, both held sophisticated electronic coding equipment with which to transmit their secret military traffic. Since 1939, Britain had been able to read most of the German and Japanese codes and may have known of the Japanese plan to attack Pearl Harbor. Did Churchill know of the attack several days beforehand and was President Roosevelt told in time? Is this why the US aircraft carriers sailed from Pearl Harbor before the fatal attack?