D-Day

However, many other invasions and operations had a designated D-Day, both before and after that operation.

The terms D-Day and H-Hour are used for the day and hour on which a combat attack or operation is to be initiated. They designate the day and hour of the operation when the day and hour have not yet been determined, or where secrecy is essential.

For a given operation, the same D-Day and H-Hour apply for all units participating in it.

When used in combination with numbers, and plus or minus signs, these terms indicate the point of time preceding or following a specific action.

Thus, H−3 means 3 hours before H-Hour, and D+3 means 3 days after D-Day. (By extension, H+75 minutes is used for H-Hour plus 1 hour and 15 minutes.) Planning papers for large-scale operations are made up in detail long before specific dates are set.

Thus, orders are issued for the various steps to be carried out on the D-Day or H-Hour minus or plus a certain number of days, hours, or minutes. At the appropriate time, a subsequent order is issued that states the actual day and times.

The Normandy landings, codenamed Operation Neptune, were the landing operations on 6 June 1944 (termed D-Day) of the Allied invasion of Normandy in Operation Overlord during World War II. The largest seaborne invasion in history, the operation began the invasion of German-occupied western Europe, led to the restoration of the French Republic, and contributed to an Allied victory in the war.

Planning for the operation began in 1943. In the months leading up to the invasion, the Allies conducted a substantial military deception, codenamed Operation Bodyguard, to mislead the Germans as to the date and location of the main Allied landings. The weather on D-Day was far from ideal, but postponing would have meant a delay of at least two weeks, as the invasion planners set conditions regarding the phase of the moon, the tides, and the time of day that meant only a few days in each month were deemed suitable. Hitler placed German Field Marshal Erwin Rommel in command of German forces and of developing fortifications along the Atlantic Wall in anticipation of an Allied invasion.

The amphibious landings were preceded by extensive aerial and naval bombardment and an airborne assault—the landing of 24,000 British, US, and Canadian airborne troops shortly after midnight. Allied infantry and armoured divisions began landing on the coast of France starting at 06:30. The target 50-mile (80 km) stretch of the Normandy coast was divided into five sectors: Utah, Omaha, Gold, Juno and Sword Beach. Strong winds blew the landing craft east of their intended positions, particularly at Utah and Omaha. The men landed under heavy fire from gun emplacements overlooking the beaches, and the shore was mined and covered with obstacles such as wooden stakes, metal tripods, and barbed wire, making the work of the beach clearing teams difficult and dangerous. Casualties were heaviest at Omaha, with its high cliffs. At Gold, Juno, and Sword, several fortified towns were cleared in house-to-house fighting, and two major gun emplacements at Gold were disabled using specialised tanks.

The Allies failed to achieve all of their goals on the first day. Carentan, St. Lô, and Bayeux remained in German hands, and Caen, a major objective, was not captured until 21 July. Only two of the beaches (Juno and Gold) were linked on the first day, and all five bridgeheads were not connected until 12 June. However, the operation gained a foothold that the Allies gradually expanded over the coming months. German casualties on D-Day were around 1,000 men. Allied casualties were at least 12,000, with 4,414 confirmed dead. Museums, memorials, and war cemeteries in the area host many visitors each year.