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World War II
A Narrative History

"The Price of Ultra"
Anthony Cave Brown
Bodyguard of Lies, Vol. 1 (1975)

In the aftermath of the Coventry Raid
Defeated in its attempt to gain aerial superiority over England [in the Battle of Britain], the Luftwaffe soon changed its tactics and resorted more and more to night bombing, a campaign that, while it hurt Britain grievously and destroyed large areas of many of her major cities, could not be decisive. Ultra had helped thwart a German invasion, but the time was fast approaching when Britain would have to pay a high price for "my most secret source," as Churchill called Ultra. The cost concerned a city called Coventry.
On the morning of November 12, 1940, a number of command directives began to issue from the headquarters of the Luftwaffe to the headquarters of the German air fleets in western Europe. They were quickly unbuttoned by "The Bomb"* and there emerged plans for what the Germans called "Moonlight Sonata" -- a raid in great strength for the night of November 14/15, 1940, against the cathedral and industrial city of Coventry. As Bletchley transmitted the Ultras through MI-6 to the Prime Minister's war bunker, it became clear that the Germans intended the same fate for Coventry as they had visited upon Rotterdam on May 14, 1940, when they attacked and razed the old inner city and killed nine hundred people. They had used only 57 Heinkel III's in the Rotterdam raid, but Ultras revealed that they would send 509 Heinkels over Coventry -- and the results were expected to be correspondingly more devastating.
The Luftwaffe's target was a city of around a quarter of a million people, living in some 30 square miles of urban area about 90 miles northwest of London in the heart of the Midlands. Coventry had architectural, historical and industrial importance. It was founded in 1043 when Leofric, Earl of Mercia, and his wife Godgifu, the Lady Godiva of legend, built a Benedictine monastery there. The cathedral, St. Michael's, for which the first stones were laid in the fourteenth century, was regarded as one of the finest examples of the perpendicular style of architecture in England .... Coventry's industrial importance was great; it was one of Britain's main arsenals. Armstrong Whitworth made bombers; Alvis made aero engines; Daimler, Hillman, and the Standard Motor Works made armored fighting vehicles, trucks and cars. The largest machine tool works in the world at that time was also located there; and so were the Coventry Radiator and Press Company, the British Piston Ring Company, and firms producing precision instruments, electrical and telecommunications equipment, and agricultural machinery. Such was the fabric of the city whose destruction was now threatened.
The motive for Moonlight Sonata was revenge. On the evening of November 8, 1940, just at the time Hitler was to have addressed the old guard of the Nazi Party in the Lowenbraukeller of Munich to commemorate the seventeenth anniversary of the Beer Hall Putsch of 1923 -- Hitler's first attempt at revolution, which collapsed in a gunfight with police -- the RAF made a small, provocative raid on Munich. Hitler was not caught by the raid; he left the Lowenbraukeller some ninety minutes before the first RAF bombers arrived. But in the attack the hall was bombed, there were a few casualties, and some slight damage was done to homes and shops around the railyards. The German communique on the raid alleged that the attack had been directed "exclusively against civilian dwellings, monuments, and the civilian population," and declared menacingly: "There will be particularly heavy retaliation against England." The retaliation was Moonlight Sonata.
The Ultra intercepts showed that, in addition to Coventry, two other major British cities -- Birmingham (Operation Umbrella) and Wolverhampton (Operation All-One-Piece) -- were to be attacked in the moonlight period of November 1940. They also showed in some detail what German tactics against Coventry would be. The raid was to be led by the famous Kampgruffe 100, a Pathfinder force based at Meucon, near Vannes in Brittany. These aircrfat were to fly to Coventry down a radiobeam system known as the X-Gerat, and they would bomb with incendiaries to start fires that would act as beacons for the main bomber force .... It is uncertain whether the Ultras showed what armament the Germans intended to use; it is probable, but in the event they would drop some 150,000 incendiaries, 1400 high-explosive bombs and 130 parachute mines, bombing the fires created by Kampgruffe 100 in order to shatter the water mains upon which the fire brigades would depend. And then to increase the volume of fire and to make it impossible for the fire brigades to concentrate their efforts against the main fires, the bombers would attack in waves, using incendiary and high explosive alternatively.
Ultra gave Churchill and his advisers at least forty-eight, possibly sixty, hours' warning of the devastating raid that was planned for Coventry. When the Luftwaffe intercepts reached Churchill's headquarters he gave instructions that their contents were to be kept to the smallest possible circle as he and his advisers debated the defense options open to them. There were many such options available, but throughout their discussions one factor was of paramount importance -- the security of Ultra. All knew that if any but the usual defensive measures were undertaken for the protection of Coventry, the Germans would suspect that the British had received forewarning of the raid, perhaps through cryptanalysis, and that suspicion might lead them to conclude that Enigma had been penetrated and so change to a new cipher system. How important was the security of Ultra? Was it more important than the security of a major industrial city? It would be for Churchill alone to decide.
While the defenses against night bombing attacks were then extremely primitive, there were several measures that could be taken to protect Coventry. The first was to frustrate the raid at the outset by using all available aircraft in an operation that was codenamed "Cold Douche." Through Ultra and the RAF Y service -- the technical wireless intelligence services -- the British had accurate and detailed knowledge of the location and strength of the German air squadrons in western Europe. Cold Douche proposed, therefore, that the RAF attack the bombers when they were most vulnerable -- as, heavily laden, they assembled and took off from their airfields. Then it was intended that the German bomber streams should be harassed all the way to the target to force them to disperse or to drop their bombs at sea or over open countryside and flee ... But in the event, as Wing Commander Asher Lee, the Prime Minister's air intelligence adviser, would later acknowledge, Cold Douche was "sadly and badly conceived." Intruder operations were undertaken, but they were so ineffective and on such a small scale that they failed to stop or to break up the German bomber formation.
Various schemes to assassinate the pilots of Kampgruffe 100 were also considered; all were rejected because time was too short .... But there was time to increase -- even concentrate -- anti-aircraft, searchlight and smokescreen defenses, and fire-fighting and ambulance services around the city. A combination of guns and searchlights might at least force the Germans to fly high or throw off their aim.There were 410 mobile anti-aircraft guns then available in Britain, and any or all of them could have been speeded to the defense of Coventry. But that might compromise the security of Ultra. Coventry's anti-aircraft defenses would not be reinforced, nor those of Birmingham against the attack that Ultra had revealed would fall five days after the raid on Coventry  ....
But if no extraordinary defensive measures could be taken to protect Coventry, might not a confidential warning that their city was about to be attacked on a large scale be given to civic authorities and to the fire-fighting, ambulance and hospital services? Should not the population of the inner city, together with the aged, the young, and those in hospitals who could be moved, be evacuated? To all these propositions, Churchill said no; there must be no evacuations and no warnings. To do so might cause panic among the population, panic that could result in far more casualties than the actual bombing; and, again, it would alert the German intelligence service to the fact that the British had foreknowledge of the raid ....
It was a tragic decision for Churchill to have to make, but it was the only way to protect Ultra. Ultra had already proved to be a weapon of decisive importance in the Battle of Britain, and Churchill could not risk losing what he hoped would become -- what, indeed, did become -- one of the principal weapons of victory in the war ....
The night of November 14/15, 1940 was brilliantly moonlit, there was little or no industrial haze, and the city of Coventry lay bathed in bright silver light. The air-raid sirens sounded at 1905 hours; five minutes later the drone of the Heinkels was heard overhead. Only then were the police, hospital, fire and civil defense teams aware that the city was to be attacked ....
Throughout the city it was the same story: surprise and then disaster. Defiant and Blenheim night fighters were ineffectual in dislocating the German bomber streams, and there was not enough anti-aircraft gunfire to keep them high. Within minutes of the warning, the city was showered with incendiaries, followed by the dull thud of high explosives. Moonlight Sonata was being carried out in exactly the way that Ultra had foretold, and Hitler got his revenge for minor damage to a Munich beer hall by destroying St. Michael's Cathedral.
The ravaged cathedral became a symbol of British heroism. It might just as well have been a symbol of sacrifice. St. Michael's need not have been destroyed, for the fire that attacked it was a very small one at first, and had emergency water supplies been arranged beforehand, it could have been saved. As an anonymous police sergeant recorded: "....We could see it would not be very hard to put out, but nothing happened when the water was turned on. The water mains were fractured and no water was coming through! Water was eventually found in Prior Street, but it was too late to save the most famous building in Coventry ...."
There were hundreds of similar episodes throughout the city. Parts of Coventry were smashed as flat as Rotterdam. A total of 50,769 houses were destroyed or damaged. All that remained of Christ Church was the ancient spire of Grey Friars. The sixteenth-century half-timbered Ford's Hospital was smoldering wood. The Standard Motor Works and the Radiator and Press Company were badly damaged, together with some twelve plants associated with aircraft production and nine other factories. The disruption of public utilities made work at other factories impossible. Nearly two hundred gas mains were broken, and so were countless power lines, water supply mains, sewage disposal systems, telecommunications. All railway lines were blocked and all roads were more or less impassable with rubble .... The destruction of some five hundred shops handicapped the distribution of food.
The raid lasted ten hours, and Moonlight Sonata accomplished its mission. A German reporter with the bombers called it "the greatest attack in the history of aerial warfare" .... Only one German bomber was shot down by anti-aircraft fire near Loughborough as it was making its way toward Coventry. Although the RAF flew 165 sorties that night, it reported seeing only seven intruders, of which two were attacked -- neither with any success.
Could more have been done to save the city? The answer is yes. More was done to defend Birmingham and Wolverhampton. In the case of the former, the RAF sent twenty-four Hampden bombers over the city to lay an aerial minefield. In the case of the latter, the raid was frustrated altogether because the Germans became aware that the anti-aircraft defenses had been suddenly strengthened -- information they obtained, presumably, through their wireless intelligence service. Certainly something might have been done to bring additional civil defense and fire-fighting reinforcements into or near Coventry, but ... that was not done until dawn, when the raid was over.
The New York Times correspondent in London visited Coventry after the raid and reported: "Coventry is now like a city that has been wrecked by an earthquake...." The Times (London) called Coventry a "martyred city." And indeed it was -- martyred in part to Ultra. For some 554 of its citizens had been killed ... and another 865 seriously wounded. Some 4000 citizens suffered other wounds and burns, and their city lay in devastation. Such was the price paid for Ultra.
*see War Stories: Ultra
Bodyguard of Lies is available from AMAZON

Codename for the cipher machine, developed from a design patented by a Dutchman, H.A. Koch, in 1919 from which ULTRA intelligence was derived. Dr. Arthur Scherbius, a Berlin engineer, marketed it in 1923; by 1929 he had been bought out by the German Army and Navy, which used different versions of it. So, in turn, did the Luftwaffe, the SS, the Abwehr, and the Reichsbahn (German state railways). The machine seemed to the Germans to be wholly unbreakable: even in its simplest form, for every letter it sent there were hundreds of millions of possible solutions. They forgot that no letter could stand for itself; and they forgot that the machine had no number-keys, so that figures had to be spelled out. These gave their potential opponents toe-holds enough. The Poles were reading some Enigma traffic as early as 1932, the French in 1938, the British in 1940, with startling results.
Oxford Companion to World War II, Dear and Foot, eds. (1995)
 Heinkel (He 111 bomber)
Longest-serving medium bomber of the Luftwaffe, the Heinkel He 111 stemmed from a design by Siegfried and Walter Gunther for a dual-purpose commercial transport/bomber produced in 1934 and flown on 24 February 1935 .... He 111Ps with DB 601Aa engines were delivered to the Luftwaffe in 1939 before production switched to the most widely-used variant, the He 111H with Junkers Jumo 211 engines; sub-variants of this series formed the backbone of the Luftwaffe's bomber force between 1940 and 1943; they took part in numerous raids in the Battle of Britain and were flown by the Pathfinder unit, KGr 100 .... [P]athfinder versions with special radio were the 111H-14 and He 111H-18; the He 111H-16 featured increased gun armament, and the He 111H-20 included 16-paratroop transport, night bomber and glider tug sub-variants. The He 111H-22 carried a single Fi 103 flying bomb and was used against the UK late in 1944. The most extraordinary of all was the He 111Z (Zwilling, or Twin) which consisted of two He 111Hs joined together with a new wing and fifth engine; it was used mainly to tow the huge Me 321 Gigant gliders. A total of about 7,300 He 111s was built.
Heinkel He 111H-16
Type: five-crew medium bomber
Powerplant: two 1,350 hp (1007-kW) Junkers Jumo 211F inverted V-12 piston engines
Performance: maximum speed 436 km (271 mph) at 6000 m (19,685 ft); .... service ceiling 6700 m (21,980 ft); range 1950 km (1,212 mi)
Weights: empty 8680 kg (19,136 lb); maximum take-off 14000 kg (30,865 lb)
Dimensions: span 22.60 m (74 ft 1-3/4 in); length 16.40 m (53 ft 9-1/2 in); height 3.40 m (13 ft 1-1/4 in)
Armament: one 20-mm MG FF cannon in nose, one 13-mm (0.51-in) MG 131 gun in dorsal position, two 7.92-mm (0.31-in) MG 15 guns in rear of ventral gondola and two 7.92-mm MG 81 guns in each of two beam positions, plus a bombload of 2000 kg (4,409 lb) internally and 2000 kg externally