When the Allied invasion fleet crossed to Normandy on the night of June 5/6, 1944, it did not meet a single attack by the Luftwaffe or by enemy E- or U-boats. When our parachute troops were dropped a few hours before the assault they landed with negligible casualties, though we had expected a 25 per cent loss. After our initial landings the enemy held back his main reserves for 18 or 48 hours, and enabled us to secure a firm foothold.
These were the chief results of the greatest hoax in military history – a hoax carried out almost entirely by 105 aircraft of the Royal Air Force, by 34 small ships of the Royal Navy, and by R.C.M. (Radio Counter Measures). In the planning of Operation “Overlord” (the code word for the Normandy invasion) it was considered essential that the enemy should be made to believe that the assault would come not on the Normandy beaches but farther north in the Pas de Calais between Cap d'Antifer and Boulogne.
This was the task of R.C.M. The responsibility for carrying it out rested with Bomber Command. But long before the operational planning could be commenced, much preliminary technical work had been carried out by the Telecommunications Research Establishment. For two months before D-Day, and for the month following our landings, Bomber Command played a leading part in the hammering of German coast defences and the “softening-up” process round the French coast. The German night fighter force, based in north-west France, invariably reacted strongly to these attacks by our bombers.
The great chain of enemy radar stations round the French coast were always equally alert. In the conviction that our technical devices were so highly developed that we could confuse the enemy into mistaking a carefully-planned feint for the real thing, R.C.M. was ready with a complicated and well-rehearsed scheme of deception.
The scheme was in five parts, each with a separate aim but linked in one general plan. The five parts went under the code names Taxable, Glimmer, Mandrel, A.B.C. Patrol, and Titanic. Their aims were (1) to simulate diversionary attacks by air and sea away from the real assault area; (2) to provide cover for the genuine airborne landings; (3) to throw the German radar system into such a state of confusion that enemy reaction to our intentions would be delayed and greatly minimized. On the night of June 5/6 the five parts of the R.C.M. plan went simultaneously into operation, as follows:
In “Taxable”, eighteen small ships of the Royal Navy steamed towards Cap d'Antifer at a speed of seven knots to suggest a landing on that part of the French coast. As enemy radar could quickly sum up the size of this force and dismiss it as not being a serious threat, one of the R.A.F.'s most experienced squadrons, No. 617 – led by Group Capt. G. L. Cheshire, V.C., D.S.O., D.F.C. – flew in support. Every minute of the 3½ hours op the operation, the aircraft of this squadron dropped twelve bundles of “Window” – the thin metallized strips which produce false echoes on the enemy radar screens and so confuse their plotting.
Flying in box formation over an area 12 miles wide and eight miles deep, the aircraft had to fly in a continuous orbit gradually nearing the French coast, to give the impression of a large convoy heading slowly towards it. The effect was heightened by the Navy ships towing balloons which would reproduce a “big ship” type of echo on the enemy radar screens, and also by our aircraft jamming the German radar to prevent recognition of the “Window” deception.
Exactly the same deception was practised in a direction heading for Boulogne. In this case (“Glimmer”) 16 ships were covered and “magnified” by 218 Squadron. In two areas in the Channel – due south of Littlehampton and due south of Portland Bill – twenty aircraft of 199 Squadron (“Mandrel”) maintained a jamming barrage which covered the enemy's coastal reader frequencies, reduced his warning system, and screened our own aircraft.
They flew at 18,000 feet at a constant distance of 50 miles from the enemy coast and with positional error of never more than five miles from ten fixed points in the Channel, and jammed the Hun radar for hours on end. In this task they were joined by four Fortresses of No. 803 Squadron of the U.S. Army Air Corps.
In the area between Taxable and Glimmer, 29 Lancasters flew for 4½ hours in “A.B.C. Patrol” to lure the enemy night fighters away from the actual landing areas. They, too, added to the confusion on the German radar by providing between them 82 jamming transmitters. A secondary reason for this patrol was the hope (speedily fulfilled) that the Germans would mistake it as top cover for the “invasion” simulated by Glimmer.
While all this was going on, dummy airborne invasions (“Titanic”) were carried out at two points – one slightly east of Fécamp, the other halfway down the Cherbourg Peninsula. Dummy parachute troops were dropped at both points; in addition, enough of the invaluable strips of “Window” were dropped to give the harassed enemy radar operators the impression that this airborne invasion was twenty times larger than it was.
The actual invasion forces sailed on their appointed course without any interference by air or sea. Through R.C.M., the enemy appreciation of the main direction of our attack was completely wrong. In R.C.M. operations on the night before D-Day only three of the 105 aircraft taking part were lost.