Gee raids on the Ruhr

War chronologies commonly list an RAF raid on Essen under 13 March 1942, and bomber raids on targets in France and Germany under 25 March. Both entries describe the same development: in March 1942 Britain’s bomber force, RAF Bomber Command, returned over Germany after a winter lull with a new commander, a new directive and a new navigational device. The first date, however, needs qualifying. Essen, the main target of the new campaign, was bombed on the nights of 8–9, 9–10 and 10–11 March. On the night of 13–14 March the bombers went to Cologne, and it was this raid, not any of the attacks on Essen, that proved the first fully successful attack carried out with the aid of Gee. The 25 March date, for its part, covers the largest operation yet against a single target, Essen once again, while the targets in France had been attacked at the beginning of the month, most notably in the night raid on the Renault works at Billancourt outside Paris on 3–4 March.

Crisis and a new course

In the winter of 1941–1942 the British bombing offensive was in crisis. Using photographs from aircraft cameras, the Butt Report of August 1941 had shown that only about one in three crews claiming to have attacked had dropped their bombs within eight kilometres of the target, and over the smoky industrial Ruhr the proportion was smaller still. After the costly night of 7–8 November 1941, when 37 aircraft failed to return from raids on Berlin, Cologne and Mannheim, the War Cabinet ordered Bomber Command to conserve its strength until the spring. The command was waiting for two things: new four-engined bombers, and a radio-navigation aid that would let crews find their targets at night.

On 14 February 1942 the Air Ministry issued a new directive. It lifted the November restrictions and stated that the primary object of operations was now to be the morale of the enemy civilian population, and in particular of the industrial workers. The list of primary targets was drawn up according to the range of the new device, referred to in the document by the code name TR 1335: it covered industrial centres up to about 560 kilometres from the airfields of eastern England, above all the cities of the Ruhr, headed by Essen, as well as Duisburg, Düsseldorf and Cologne. A day later the Chief of the Air Staff, Charles Portal, added a clarification that the aiming points were to be the built-up areas of the cities, not, for example, the dockyards or aircraft factories named in the annex. In this way area bombing, already practised before, became official policy. Targets in France, with the Renault works at their head, were relegated to second place.

On 22 February 1942 Air Marshal Arthur Harris took over Bomber Command at High Wycombe in place of the dismissed Richard Peirse. On the same day the first headquarters of the American bomber force was only just being set up in England, without a single aircraft yet. Harris had not written the directive, but he carried it out with conviction. By his own account, on the day he took command he had fewer than 400 serviceable aircraft with crews available, only a few dozen of them heavy bombers. Most of his force consisted of twin-engined Wellingtons, Hampdens and Whitleys, while the new four-engined Stirlings and Halifaxes were only beginning to reach the squadrons. On 3 March No. 44 Squadron flew the first operational sortie in Lancasters, laying mines in the Heligoland Bight.

Gee

Gee was a British hyperbolic radio-navigation system. Before the war the engineer Robert Dippy, one of the radar research team, had proposed a similar arrangement as an aid to night landing, and in 1940 he put forward a design for a navigation system; in the course of the work it turned out that the signals carried much further than expected. Three transmitters in England, a master and two slaves, sent out precisely synchronised pulses. A receiver in the aircraft measured the difference in their times of arrival, and the navigator read two values off a screen and plotted them on a special chart overprinted with a lattice of curves. The intersection of the two lines gave the aircraft’s position within a few minutes, accurate to a few hundred metres nearer the transmitters and to several kilometres at the limit of range. The range was about 550–650 kilometres, depending on altitude: enough for the Ruhr and the Rhineland, but not for Berlin.

The first operational trials took place in August 1941, but after one of the aircraft fitted with a receiver was lost over Germany they were halted so that the Germans would not learn of the device prematurely. British scientific intelligence then spread rumours of a fictitious “Jay” system to mislead the enemy. Hand-built receivers reached the squadrons from the beginning of 1942, and in March only some of the aircraft had them. Bomber Command therefore adopted a tactic called “Shaker”: a first wave of Gee-equipped aircraft was to drop illuminating flares over the target, a second, also guided by Gee, was to mark the target with incendiaries, and the main force without the new device was to bomb the resulting fires. It was expected that within a few months the Germans would learn to jam the signals; serious jamming began in August 1942.

Billancourt, 3/4 March

Before Gee was used over Germany, Harris opened his command against a target that still figured in the directives: the Renault factories on the Île Seguin and at Boulogne-Billancourt in the western suburbs of Paris. The works, still run by Louis Renault, were producing lorries for the Wehrmacht under German supervision. On the night of 3–4 March, according to British figures, 235 aircraft were sent to Billancourt, the largest number yet dispatched to a single target. The target was weakly defended, the night was moonlit, and the bombers came in low and attacked in waves. Bomber Command lost only one aircraft.

The works were badly damaged and production stopped for several weeks; British estimates put the loss at some two thousand vehicles. But bombs also fell on the densely built working-class districts of Boulogne-Billancourt and neighbouring communes. Casualty figures vary with the source: British studies give 367 French dead, French ones from about 400 to 500 dead and many more wounded. According to British historians, more civilians were killed than in any earlier RAF raid on a German city. The Vichy authorities and German propaganda made wide use of the victims in a campaign against Britain. In the following days Bomber Command attacked targets in France with smaller forces; on 8 March, according to French histories of the plant, bombs fell on the Ford factory at Poissy, halting production for several weeks. The decisive blow against Poissy came at the beginning of April.

Essen under smog, 8–11 March

On the night of 8–9 March 1942, 211 aircraft were sent to Essen, home of Krupp, the Reich’s largest armaments concern. It was the first raid led by Gee-equipped aircraft. The crew of one of the leading Wellingtons recalled that targets had been found and bombed “as never before”, and indeed, according to Bomber Command’s analyses, about a third of the aircraft reached the target area, a very good result for the time. Essen itself, however, was protected by its smog. A dense industrial haze from the chimneys of steelworks and coking plants usually hung over the Ruhr; the flares lit it up instead of revealing the city. The Krupp works were not hit. According to German figures, the bombs destroyed a few houses and a church in Essen, ten people were killed and nineteen were listed as missing; many loads fell on the southern districts and on neighbouring towns.

The next night, 9–10 March, 187 aircraft were sent to Essen. In the city itself they destroyed only two buildings, but bombs fell on some twenty other towns of the Ruhr, especially Hamborn and Duisburg, where 74 people were killed. On the night of 10–11 March more than a hundred and twenty aircraft set out for Essen, among them, for the first time over Germany, two Lancasters of No. 44 Squadron. Sixty-two crews reported attacking; one house in the city was destroyed, and five Germans and a Polish forced labourer were killed. The three nights showed the limits of the new device: Gee brought the bombers close to the city but did not let them see it, and it was too imprecise for aiming in the smoke-filled Ruhr.

Cologne, 13/14 March

On the night of 13–14 March 1942, 135 aircraft attacked Cologne. This time the tactic worked. Navigating by Gee, the leading crews lit up the target with flares and marked it with incendiaries, and the main force bombed fairly concentrated fires. According to German figures, 237 fires broke out in the city, 62 people were killed and 84 injured. Bomber Command lost one aircraft, a new and unreliable Manchester. The command’s analysts judged the raid to have been roughly five times as effective as the average earlier attack on Cologne. It was regarded as the first fully successful raid carried out with the aid of Gee, and as proof that cities within its range could be found and set on fire at night. According to British studies, in the following weeks the planners selected several dozen German cities within Gee range as targets for heavy area raids.

Essen, 25/26 March

On 21 March the Air Ministry supplemented the February directive: the Ruhr was to be attacked in concentrated incendiary raids, partly as an experiment with different types of incendiary bomb. The document referred explicitly to the effectiveness with which the Germans had used such methods during the Blitz. A few days later Harris sent his force against Essen once more. On the night of 25–26 March, 254 aircraft took part: according to the operational records, 192 Wellingtons, 26 Stirlings, 20 Manchesters, 9 Hampdens and 7 Lancasters. It was Bomber Command’s largest operation yet against a single target.

The result was disappointing. A large part of the bomber force was drawn to a decoy fire site near Rheinberg, several dozen kilometres west of Essen. The Germans built such dummy targets in open country and lit fires on them imitating a burning city as soon as the bombers approached. In Essen one house was destroyed and two seriously damaged; five people were killed. Bomber Command lost nine aircraft, five of them Manchesters. The following night, 26–27 March, 115 bombers again set out for Essen; they destroyed two houses, and eleven aircraft failed to return. The March balance over Essen was therefore meagre: several raids, a few dozen killed in the city and the Krupp works untouched, at the cost of more than twenty aircraft lost in the last two operations alone.

Place in the war

The March raids with Gee opened a new phase of the British bombing offensive, in which the target became the built-up areas of German cities rather than individual factories. Gee did not provide the precision that had been hoped for, but it allowed hundreds of bombers to be led along a common route close to the target, which made it possible to concentrate raids in time and space. Cologne in March showed that a city within Gee range and free of dense smog could be effectively set on fire; Essen showed that the Ruhr would remain a difficult target. At the end of March Harris applied this lesson to a target that was highly flammable and lay close to the coast, and was therefore easy to find at night: the medieval old town of Lübeck. At almost the same time Frederick Lindemann, scientific adviser to Prime Minister Winston Churchill, submitted a memorandum arguing that the systematic destruction of workers’ homes in the few dozen largest cities could break German morale.

In the months that followed Harris developed the method further: on the night of 30–31 May 1942 more than a thousand bombers attacked Cologne, in August a target-finding formation (the Pathfinder Force) was created, and at the turn of 1942 and 1943 more accurate devices, Oboe and the H2S radar, came into service. Only with them was Essen seriously damaged: in the spring of 1943, during the Battle of the Ruhr, bombers guided by Oboe at last hit the Krupp works and the city centre. Although the Germans began jamming Gee in the summer of 1942, it served until the end of the war as a navigational aid over England and on the way to the target, and after the war in civil aviation as well. The offensive begun in March 1942 brought about, in the years that followed, the deaths of hundreds of thousands of German civilians and the destruction of most of the Reich’s large cities; its military effectiveness and its moral assessment remain a matter of dispute among historians to this day.