About this Video
About the Video: The objective of the operation was to create a lodgement that would be anchored in the city of Caen (and later Cherbourg when its deep-water port would be captured). As long as Normandy could be secured, the Western European campaign and the downfall of Nazi Germany could begin. About 6,900 vessels would be involved in the invasion, under the command of Admiral Sir Bertram Ramsay (who had been directly involved in the North African and Italian landings), including 4,100 landing craft. A total of 12,000 aircraft under Air Marshal Sir Trafford Leigh-Mallory were to support the landings, including 1,000 transports to fly in the parachute troops; 10,000 tons of bombs would be dropped against the German defenses, and 14,000 attack sorties would be flown.
Some of the more unusual Allied preparations included armoured vehicles specially adapted for the assault. Developed under the leadership of Maj. Gen. Percy Hobart (Montgomery's brother-in-law, and an armoured warfare specialist), these vehicles (nicknamed Hobart's Funnies) included "swimming" Duplex Drive Sherman tanks, the Churchill Crocodile flame throwing tank, mine-clearing tanks, bridge-laying tanks and road-laying tanks and the Armoured Vehicle, Royal Engineers (AVRE)--equipped with a large-caliber mortar for destroying concrete emplacements. Some prior testing of these vehicles had been undertaken at Kirkham Priory in Yorkshire, England. The majority would be operated by small teams from the British 79th Armoured Division attached to the various formations.
I copied this information from wikipedia