Six days after the D-Day landing, the five Allied landing groups, made up of some 330,000 troops, link up in Normandy to form a single solid front across northwestern France. On June 6, 1944, after a year of meticulous planning conducted in secrecy by a joint Anglo-American staff, the largest combined sea, air, and land military operation in history began on the French coast at Normandy. The Allied invasion force included 3 million men, 13,000 aircraft, 1,200 warships, 2,700 merchant ships, and 2,500 landing craft. Fifteen minutes after midnight on June 6, the first of 23,000 U.S., British, and Canadian paratroopers and glider troops plunged into the darkness over Normandy. Just before dawn, Allied aircraft and ships bombed the French coast along the Baie de la Seine, and at daybreak the bombardment ended as 135,000 Allied troops stormed ashore at five landing sites. Despite the formidable German coastal defenses, beachheads were achieved at all five landing locations. At one site—Omaha Beach—German resistance was especially strong, and the Allied position was only secured after hours of bloody fighting by the Americans assigned to it. By the evening, some 150,000 American, British, and Canadian troops were ashore, and the Allies held about 80 square miles. During the next six days, Allied forces in Normandy moved steadily forward in all sectors against fierce German resistance. On June 12, the five landing groups met up, and Operation Overlord—the code name for the Allied invasion of northwestern Europe—proceeded as planned.