The city centre following the air raid of 14 November 1940.
On the night of November 14, 1940, in operation "Moonlight Sonata," which was part of the ongoing German blitz of England and the Battle of Britain, German bombers attacked and seriously damaged the industrial city of Coventry, which lies in the British midlands. During the 1970s, several former high-level British military and intelligence officials declared that the British had known in advance that the raid was coming because they had broken the German secret military codes ("Enigma") and that Prime Minister Winston Churchill had consciously decided to allow Coventry to be destroyed rather than order the evacuation and air defense of the city, which might have informed the Germans that Enigma had been compromised. While much of the history of intelligence operations during World War II remains hidden, more recent scholarship suggests that these earlier officers and intelligence agents were either mistaken or radically exaggerating their own roles in the war and that in fact Churchill never made the decision to leave Coventry unprotected in the face of Luftwaffe bombers.
"Ultra," the British system designed to break the Enigma codes, proved to be one of the most important developments of the war. The Germans were encoding their secret radio traffic by using a complex device known as the "Enigma machine." Early in the war, Polish mathematicians managed to construct one of these machines. Suspecting that they were about to be attacked by Germany, the Poles sent their notes to England, where the British set up a massive cryptography center at Bletchley Park. Using huge banks of early computers, which were known as "bombes," the Allies managed to decode many (though not all) German messages and to use the information they learned to affect the course of the war. Much of the time, the intelligence that the Allies gathered was incomplete; even unencrypted messages used code words, which were often impossible to decipher. In operation Moonlight Sonata, for instance, the city of Coventry was referred to only as "corn," while Birmingham was referred to as "umbrella," and Wolversham was referred to as "all one price." The operation itself was named "Moonlight Sonata" because, like a sonata, it consisted of three or four independent parts, and it was scheduled for a night with a full moon. Unable to interpret completely the messages they had intercepted, thus unable to determine the location of the German assault, the British were forced to attempt to intercept the German bombers at the last minute, once it had become clear where the Germans were headed. As a result, they were unable to inflict significant damage on the German planes before the German pilots dropped their bombs.
The attack on Coventry was enormously successful from the German point of view. While over one hundred British planes did manage to get into the air to defend the city, the British air force was not sufficiently prepared for the attack as they faced over four hundred German planes. (Of the 509 bombers the Germans sent to attack Coventry, 449 reached their target without getting lost; only one was confirmed destroyed by the British.) During the bombing, the Germans managed to destroy twelve armament factories, much of the city center, and the fourteenth-century cathedral in town. Civilian casualties were heavy: 380 people were killed, and 865 were wounded.
Many years after the end of the war, several former British military officers and intelligence agents published books about the roles that they had played in developing and using Ultra during the conflict. Two of the most important books (both of which were written largely from memory, without supporting evidence) were F. W. Winterbotham's The Ultra Secret, which was published in 1974, and William Stevenson's A Man Called Intrepid, which was published in 1976. Both Winterbotham, who had commanded British pilots during the war, and Stevenson (code-named "Intrepid"), who had headed the British intelligence service in the Western Hemisphere, described how they and Churchill had received intercepted German messages, thus had known in advance that the raid on Coventry was imminent. According to Stevenson, Churchill had turned to him for advice, and he had responded that the intelligence that the British were getting from Ultra was too valuable to risk losing, even if that meant that the British would have to accept the heavy civilian casualties that would come with a successful German air raid on Coventry.
While books such as Winterbotham's and Stevenson's make for interesting reading, more recent scholarship has demonstrated that they were, in fact, remembering incorrectly, or else they were manufacturing stories that did not happen. Coventry, it seems clear, was left weakly defended because the British code breakers concluded that the raid on the evening of the fourteenth would target London. At the time Coventry was being attacked, Churchill himself was waiting in his London bunker for an air raid that never arrived.