D-Day and H-Hour, terms used in military nomenclature for a basic date and time from which any event, usually an attack, can be scheduled, before the actual date and time are fixed. For example, it may be necessary to lay down an artillery barrage two days before the attack begins (D minus 2), to carry out a bombing attack five hours before the attack (H minus 5), and to have certain supplies delivered three days after the start of the attack (D plus 3). These events and many others must be planned and integrated weeks before the attack is actually scheduled to commence; the decision about the precise time of the attack, which may depend on weather, tides, or other local conditions, can be deferred until one or two days before D-Day itself. The best-known D-Day was June 6, 1944, in World War II, when Allied forces landed in northern France in the world's largest amphibious operation, the Normandy Campaign.