01Operation Overlord, the broader campaign including D-Day, was conceived in 1943 and involved detailed planning starting from the Tehran Conference in November 1943 where Allied leaders agreed on a cross-Channel invasion
02The final D-Day invasion plan, codenamed Operation Neptune, was approved by General Dwight D. Eisenhower on May 17, 1944, after numerous revisions to account for weather and tidal conditions
03Allied planners calculated that the invasion required a 5:1 superiority in troops over German forces in Normandy, leading to the assembly of over 2 million personnel in southern England by June 1944
04Operation Fortitude, a massive deception operation, convinced German intelligence that the main Allied landing would be at Pas-de-Calais, diverting 19 divisions from Normandy
05The Allies conducted 17,000 sorties by RAF Bomber Command from April to June 1944 to soften German defenses, dropping over 14,000 tons of bombs on coastal batteries
06Meteorological forecasts by Group Captain James Stagg were crucial; he predicted a narrow 6-hour window on June 6 despite poor weather, influencing Eisenhower's go-ahead decision at 0415 on D-Day minus one
07Two artificial Mulberry harbors were designed and prefabricated in Britain, each capable of unloading 7,000 tons of cargo and 2,000 vehicles daily once operational
08The Pluto pipeline project planned underwater fuel lines from England to Normandy, capable of delivering 1 million gallons of petrol per day by D+70
09SHAEF (Supreme Headquarters Allied Expeditionary Force) issued the final invasion order on May 8, 1944, detailing H-Hour as 0630 for most beaches adjusted for tides
10Allied intelligence from Ultra decrypts revealed 58 German divisions in France, but underestimated the 7th Army's mobile reserves near Caen
11The invasion required 16,000 French Resistance fighters to sabotage rail lines, cutting 295 locomotives and destroying key bridges on D-Day eve
12Over 12,000 aircraft were allocated for air superiority, with 9,500 from RAF and USAAF based in 129 airfields across southern England
13Naval bombardment plans included 7 battleships, 23 cruisers, and 121 destroyers to fire 10,000 tons of shells in the first hour on D-Day
14The Allies stockpiled 1.5 million tons of supplies in 194 ports across Britain, including 500,000 tons of ammunition for the first 14 days
15Paratrooper drop zones were rehearsed in mock invasions like Operation Tiger on Slapton Sands, which tragically cost 749 lives due to friendly fire
16General Montgomery's plan divided Normandy into British sector (Caen) and American (Cotentin), with objectives set 10 miles inland by D+5
17Waterproofing kits for 15,000 vehicles were developed, adding canvas seals and exhaust extensions to allow wading through 4 feet of water
18The Horsa glider could carry 28 troops or a Jeep with gun, with 2,558 launched on D-Day from 24 airfields in southern England
19Signal plans included 500,000 homing pigeons trained for message relay if radios failed due to German jamming
20Beach obstacle charts were drawn from 1943 Commando raids like Dieppe, identifying 6 types including Belgian Gates and tetrahedrons
21The invasion tide was calculated for a full moon on June 5-7 for optimal glider landings with bright nights
22156,000 troops were to be landed in first wave, supported by 20,000 vehicles including 1,600 tanks across 5 beaches
23SHAEF printed 100 million maps and 17 million air photos for troops, with each soldier receiving a personal escape kit with French francs
24Operation Bodyguard included fake army FUSAG under Patton, with inflatable tanks and dummy radio traffic fooling German spies
25RAF dropped 13,000 tons of bombs on French rail yards from June 5-7, reducing German reinforcements by 50% initially
26Naval Force U for Utah Beach planned 220 ships, including USS Texas firing 2,500 shells from 14-inch guns pre-H-Hour
27Engineers planned to clear 50-yard gaps through obstacles on each beach using 100 Duplex Drive tanks and 200 LCVPs
28The cross-Channel convoy route "Spunyarn" was 80 miles long, zigzagging to avoid U-boats with 7 destroyer escorts
29Medical evacuation plans included 59 hospital ships and 500 LCAs fitted as casualty carriers for 10,000 wounded on D-Day
30Airborne pathfinders with Eureka beacons were to mark 9 drop zones with radar signals every 10 seconds starting 0030 June 6