From 1942 to 1943 he served as assistant adjutant – General of the Army in Washington, D.C., before joining the
12th Army Group in Europe to help plan
operation Overlord, the Normandy Invasion in 1944. During the planning of the invasion, and in subsequent operations in France and Germany, he established and integrated the Adjutant General Section of Headquarters,
United States Army Adjutant General's Corps and formulated the policies under from which the department would operate. His untiring efforts, leadership, tact and sound judgment were largely responsible for the efficient operation of the command. He served as Omar Bradley's deputy chief of staff and adjutant general until the end of the war. The
Twelfth United States Army Group was the largest and most powerful United States Army formation ever to take to the field. It controlled the majority of American forces on the Western Front in 1944 and 1945. It was commanded by General
Omar Bradley with its headquarters established in London on July 14, 1944. Bradley's
First United States Army, which later formed part of the Twelfth Army Group, formed the right wing of the Allied lines during the Normandy landings and the Battle of Normandy. They were joined during July by the
Third United States Army, under the command of General
George Patton. Until September, when General
Dwight D. Eisenhower assumed overall command of the Allied land forces in Northwest Europe, the U.S. forces in Normandy were included with the British Second Army and the First Canadian Army in the British headquarters formation 21st Army Group, commanded by Field Marshal
Bernard Montgomery. After the breakout from the beach-head at Normandy, the Twelfth Army Group formed the center of the Allied forces on the Western Front. To the north was the British 21st Army Group (the 2 aforementioned field armies) and, to the south, advancing from their landing on the Mediterranean coast, was the Sixth United States Army Group (Seventh United States Army and French First Army). As the Twelfth advanced through Germany in 1945, it controlled four field armies: First United States Army, Third United States Army, Ninth United States Army and Fifteenth United States Army. By V-E Day, the Twelfth Army Group was a force that numbered over 1.7 million men. For his exceptionally meritorious service as adjutant general, Lewis was made an Honorary Commander of the
Order of the British Empire after being recommended by both General
Omar Bradley and Field Marshal
Bernard Montgomery. == After the war ==