Since 1942 German Intelligence had been receiving valuable intelligence from their man in Britain. The fanatical fascist, a Spanish Government official, had volunteered to work for them. After the initial information they received from him had proved credible, in 1942 they had instructed him to try to move to Britain. He got a posting to Britain. The Germans had then supplied him with a radio so he could transmit his findings directly to them, rather than posting them to Portugal.
The Germans knew him as ARABAL and he had proved incredibly useful, building up a string of contacts and other spies around Britain who reported to him. In Glasgow, Scotland, in the north of Britain, was Carlos, a Venezulean student, codename BENEDICT. He was ideally placed to watch the shipping movements and troops coming in from the United States.
He had also proved very valuable in reporting on the large numbers of troops that stayed in Scotland. They were not all sent down to the Channel Coast. From this the Germans had learnt that there would probably be an invasion of Norway launched from Scotland. They had been able to confirm this by listening to radio messages sent by Polish and American troops stationed in Scotland.
Now they received further confirmation as he reported on a local amphibious troop exercise, which ARABAL reported by radio to Germany:
. . . .V BENEDICT, UNDERTAKING ARABAL 10/5 from England via FELIPE: . . . . I estimate that up to 1100 hours more than a bde. of the div. had landed. Landing of troops was continued in a similar way.
Apart from the transports which brought the landing craft I was able to see another 10 transports, which lay in the neighbourhood and were doubtless connected with the exercise. One of these transports flew the flag WHITESIGN (sic) had a remarkably large number of aerials on board and continually sent light signals with searchlights to the shore.
The exercise lasted until the 11/5.
General impression gained by the VM on the basis of what he ascertained during the exercises and former information about this division is that it is intended for action in Norway as the division is continually receiving training in mountain warfare and all its equipment points to the probability of its going into action in northern regions. Have taken all measures to continue to watch every movement of transport fleet and troops.
This was just what the Germans wanted to hear. Hitler had already transferred troops to Norway on the basis of this information. Now they instructed ARABAL to get more information about the different units in the Allied Army:
It is to be assumed that the forces which will be engaged in the invasion operation will be divided into several independent armies, British and U.S. It would be of the greatest interest to know how many armies there will be and how many have already been formed. Headquarters and names of the commanders of each Army as well as their composition, i .e. , corps and divisions under command, the objectives assigned to each army.
ARABAL was delighted to hear this, because that was exactly what his British friends wanted him to do anyway. ARABAL is better known today by his British code name GARBO. He was the double agent who was feeding false information directly to German intelligence. BENEDICT was a complete work of fiction, as were the large army in Scotland about to invade Norway, and the even larger First US Army Group, FUSAG, supposedly commanded by Patton, who would launch a second invasion after the Normandy landings.
Read more about GARBO at the Security Service, MI5