The battle in 1944 that turned the tide in favor of the Allies in Western Europe was the Battle of Normandy, commonly known as D-Day. It began on June 6, 1944, with the Allied landings on the beaches of Normandy, France. This massive operation involved extensive planning and coordination among Allied forces, resulting in a crucial foothold in Nazi-occupied Europe. D-Day was the largest amphibious invasion in history and marked the start of a significant offensive that ultimately led to the liberation of Western Europe from Nazi control.