Why is the Normandy Invasion called D Day?

Answer 1

D-Day was the name chosen by General Frederick Morgan's COSSAC planning group

Correct answer:D-Day & H-Hour are used in military planning processes. During the Second World War it became associated with the invasions of the Allies in various theaters.

For an invasion such a the Normandy invasion of June 6, 1944 the 'D' is the Day of the invasion, and the 'H' is (for example) the hour that the shore bombardment started. This allows all events prior to the planned invasion to be labeled as D minus 1, or D minus 2, etc.,; and all events after the invasion to be labeled as D plus 1, D plus 2, etc. Likewise there is H minus 1, H minus 2, etc.; and H plus 1, H plus 2, etc.

This is an identical planning method used in US Military & NASA space launches that you will recognize: "T minus 2 minutes & counting", "T minus 30 seconds& counting", "we have main engine start" (which is T), "the rocket has cleared the tower and is traveling at 500 feet per second at T plus 30 seconds", and so forth.

Going back to military operations that are kept secret as to the date & time of the start, it is much more practical & easier for the planners to schedule all the thousands of important tasks or events in terms D-Day (plus or minus 1, 2, 3, etc.) and H-Hour (plus or minus 1, 2, 3 etc.).

Here is a simplistic example of how events for an amphibious invasion might look on this time schedule method for an invasion:

D minus 10: Fighters achieve air superiority within 200 miles of the landing zones.

D minus 5: Bombers begin destroying all bridges across River X& River Y to prevent enemy reinforcements.

D minus 2: Bombers have destroyed all bridges across River X& River Y to prevent enemy reinforcements.

D minus 3: Submarines hidden in position along flanks of invasion fleet routes to landing zones.

D minus 1: Invasion Fleet departs embarkation ports.

H minus 14: Transport aircraft carrying Paratroopers begin taking off from airfields.

H minus15: Final 'Go' or 'No-Go' orders are issued to transport aircraft before they approach the enemy territory.

H minus 12: Paratroopers begin parachuting into drop zones inland behind the landing zones.

H minus 10: Naval Minesweepers start clearing lanes through the minefields (at sea).

H minus 5: Naval Minesweepers complete the clearing of the lanes through the minefields (at sea).

H minus 3: Surface Bombardment warships begin passing through minefields to firing positions.

H minus 1: Surface Bombardment warships reach their firing positions.

H minus 1: First Wave troop transports begin passing through minefields to debarkation positions.

H minus 0 (H-Hour): Surface Bombardment warships open fire on their assigned primary targets.

H plus 2: First Wave troop transports arrive at debarkation positions.

H plus 3: First Wave troop transports launch landing crafts towards the assembly areas off-shore from the landing zones.

H plus 4: First Wave landing craft begin approach towards the landing zones from the assembly areas.

H plus 4hrs & 30 min: First wave landing craft are within 1,000 yards of making landfall on the landing zones.

H plus 4hrs & 30 min: Surface Bombardment warships shift fire from the primary targets at the landing zones to the secondary targets further inland.

H plus 7: First Wave troops have seized the landing zones, and Second Wave troops are breaking out of the landing zones to seize their primary-immediate objectives.

H plus 12: Second Wave troops have seized their primary-immediate objectives, and the Third Wave troops are passing through the main line of resistance to seize their objectives.

D plus 0 (D-Day): Fighters & bombers shift air support efforts east of river X to interdict & destroy enemy forces attempting to attack the invasion forces.

D plus 1: All primary objectives seized by the ground forces.

D plus 2: Follow-on forces begin landing on-shore.

D plus 5: Follow-on forces have seized their objectives.

D plus 6: Forward airfield is operational within the landing/invasion area. Aircraft flown in.

Answer 2

The D in D-Day does not stand for anything except being the capital letter of Day.