[Jim O]

He had to have had some help if he actually knew the code names of the Normandy beaches and their locations. Even the Germans were fooled by the mock concentration of troops opposite Pas-de-Calais and associated misinformation about an invasion of Norway.

From Operation Overloard: The invasion of Fortress Europe:

The Transportation Plan was carried out by more than 11,000 fighters and bombers (in comparison to the Luftwaffe's defense of 400 aircraft) which dropped 195,000 tons of bombs during more than 200,000 sorties or runs.17 These bombs were dropped on rail and road networks, German airfields, radar centers, military bases, and artillery batteries, to pave the way for the Allied troops that would follow. Not all of the bombs were dropped in the invasion areas in an attempt to convince the Germans that they would be attacking at Pas-de-Calais, in fact, only one-third of the bombs were dropped near the Normandy invasion area.....


...The reconnaissance and deception activities carried out by the Allies, also gave them a large advantage over the Germans. The German preparation was also hampered by the activities of the French Resistance. There were three major operations going on to support the invasion. They were code-named, Ultra, Fortitude, and the Double Cross System.

Ultra was the Allied operation that decoded the German Enigma-encoded radio communication with computers. The information gathered from Ultra allowed the Allied planners to know where the German troops were and to where they would be moving. It also allowed them to know where the Germans believed the Allies were coming from and what they knew about the status of the invading army.

Fortitude was the main deceptive operation. It involved the creation of a fictitious FUSAG (First United States Army Group) which was poised to "invade" Norway. FUSAG was created by sending officers to Scotland who created radio traffic in a easily decoded cipher that mimicked that of a real invading army. This was also backed up by British Commando units that were sent to the shores of Norway as well as reconnaissance planes, in general trying to look like a pre-invasion force. Hollywood and other prop designers were also shipped to England where they created rubber and wood tanks, bombers, trucks, boats, ships, and other military vehicles, so that the Germans would over-estimate the amount of Allied troops and have to spread out their forces. Other fictitious armies were also created, some of them actually real, but still back in the US or fighting in the Pacific.

Operation Fortitude was helped to seem "real" by the efforts of the British Double Cross System. At this point in the war, all of the German spies in Britain had been turned into double agents, creating the Double Cross System. This system was used to reinforce the German's belief of a huge Allied army that was poised to invade Norway, Pas-de-Calais, and a feint at Normandy. These wild reports from the spies caused the Germans to first move massive amounts of troops to Norway and then to the Mediterranean, then to Pas-de-Calais, and back. Even well after the June 6 invasion Hitler was waiting for the "real" attack in Norway...