Operation Overlord, the code name for the Allied invasion of France's Normandy region, began June 6, 1944, and had landed one million troops by July 1. The operation was under the command of United States General Dwight D. Eisenhower. For two months preceding D-Day, British-based aircraft methodically bombed rail lines, bridges, and air fields in France. Throughout the night before the invasion, paratroops were dropped inland to disrupt enemy communications. Naval guns pounded shore installations, and in the early daylight at low tide about five thousand Allied ships approached the Normandy coastline. At Omaha Beach, pivot of the landings, U.S. troops securing their bridgehead were met by heavy German gunfire. Within five days, sixteen Allied divisions had landed at Normandy and the final drive to liberate Europe was underway.