The document discusses Operation Overlord and the Allied invasion of Normandy (D-Day) on June 6, 1944. It provides context for D-Day by noting that by 1944, the Axis powers had been defeated in North Africa and parts of Italy and Russia. It also discusses the Allied strategies agreed upon at the 1943 Tehran Conference, including launching an attack to invade France and Russian offensives to liberate countries in Eastern Europe. Additionally, it describes some of the extensive preparations for the Normandy landings, including constructing artificial harbors and laying pipelines to supply the Allied forces.