D-Day 6th June 1944

One morning in early May 1944, under conditions of the greatest security W/Cdr G L Cheshire, Officer Commanding No. 617 Sqn, and his crews were informed that they were being screened from further operations. Sworn to secrecy, the crews were informed that they would not operate again until the Allies invaded the continent. Their task then would be to carry out an operation designed to deceive the Germans as to the true location of the Allied landings. The intention was to create the impression on enemy radar of an invasion fleet approaching the French coast at a location well away from the real invasion beaches. It was hoped that this, along with other “spoof” operations would cause confusion as to the true nature and extent of the landings.  

But how could an aircraft flying at nearly 200 mph possibly simulate shipping approaching the coast at a speed of 7 knots? The Telecommunications Research Establishment had devised a theoretical plan whereby an aircraft could do so using Window (strips of metal foil, today known as Chaff), by flying a pattern of elongated rectangular orbits, each with its long sides perpendicular to the French coast. As the aircraft completed each leg flying towards the coast it would delay its turn slightly, thus creating a pattern of overlapping orbits. By adjusting the timing of the turn, the shorter side presenting a “front” parallel to the coast could be made to advance towards it at a speed approximating to the speed of an approaching convoy. By using varying lengths and densities the pattern created on any watching radar screen would appear similar to that of an approaching convoy of ships. 

It was left to the Squadron to convert the basic idea into an operational reality. Split second, accurate navigation was essential. This was achieved by using Gee, an electronic navigation aid that enabled the navigator to determine his position with great accuracy and instruct the pilot when to turn. 

The crews were sent off on cross country flights to practice. No Window was dropped as the Lancasters orbited,  seemingly pointlessly, overhead for an hour at a time. Pilots had to be able to fly identical orbits, making perfectly timed turns for circuit after circuit. Accurate height had also to be maintained, achieved with a radio altimeter, combined with a constant airspeed. Any error would cause the German radar image of the “convoy” to suspiciously change position or appear to increase speed. It was tiring, monotonous work, requiring intense concentration. Each aircraft carried an additional pilot and navigator to ease the workload.  

As the aircraft ran towards the coast on each long leg, progressively larger Window strips had to be dispensed, the strips getting lighter as it flew away. The bundles of Window were stacked in the correct sequence in the aircraft and additional crew were carried as dispensers, assisted by another crew member with a stop watch and chart to ensure that the right size Window was dispensed at precisely the right time. It was hard physical work. Some 36 bundles of Window had to be dispensed on each of the straight legs. 

The Squadron carried out further practices against a radar station at Flamborough Head, this time actually dropping Window. After weeks of intensive training they had perfected the art. A further modification was then made to the plan. Because of the concentration required, the operation would be carried out in two waves, the second taking over from the first half-way through to carry the deception on to its stop line off the French coast. 

After a final briefing on the evening of 5 June the first wave of 8 aircraft departed shortly after 2300. Setting course from the Sussex coast near Littlehampton the Lancasters reached their start point 30 miles from the French coast. From there they began orbiting in four rows, line abreast at 3,000 feet, moving gradually towards Cap d’Antifer, east of Le Havre. A small flotilla of naval vessels operated independently beneath them, some flying balloons with reflectors to amplify radar returns. To add to the realism, limited jamming was deliberately employed allowing the enemy radar sufficient vision to detect the spoof “invasion fleet”. 

After thirty orbits, each lasting seven minutes, the second phase of 8 took over. A 90 second overlap ensured that there would be no gap in the Window dropping. The operation proceeded uneventfully. By dawn the last wave of aircraft were nine miles from the French coast. Some thirty minutes later they completed their final orbit and headed for home.  

It is impossible to determine the individual effectiveness of TAXABLE with any certainty. It was too close to the real invasion beaches, and fighter bomber attacks may have significantly reduced radar cover in the area.  However one thing can be certain. Along with a similar operation, GLIMMER, carried out off Boulogne by eight Stirlings of No. 218 Sqn, and other deception operations, TAXABLE caused sufficient confusion to delay the despatch of reinforcements that might have made the Normandy landings a much harder fought battle.