On 10 November the British authorities were aware that German beam transmitters had been issued with data for bomb-release points in Wolverhampton (target 51), Birmingham (target 52) and Coventry (target 53) with the clear inference that these centres would come under attack in the near future. There was nothing to indicate that these would be major assaults and both Birmingham and Coventry had featured in earlier deciphered instructions to the transmitters:

Thanks to Ltn. Probst, the RAF was aware that Regenschirm and Mondschein Sonate were the names of major operations against these cities. It was not certain which was which, or whether they would come successively (as Probst claimed but winter weather made unlikely) or on the same night. By mid-afternoon of the 15th it was known that V. Fliegerkorps had sent out out the following order:

Operations on 15/11/40: KG 51, 54 and 55 to rest during the day. Preparation for attack UMBRELLA (REGENSCHIRM).

In Bletchley’s report at 17.15 BST there was a further comment on the above:

It is suggested that UMBRELLA is BIRMINGHAM.

It is not clear how this was decided but in the event that night’s main target was London and it was not until the 16/17th that a decrypt again yielded the cover name. The original message had gone out at 13.15 GMT on the 15th, telling KGr. 100 to use the REGENSCHIRM frequency of 4500 khz, “higher than yesterday.” Instructions for KGr. 126’s radio procedures were given at the same time. From these messages it looks as if the Luftwaffe planned to attack Birmingham on the 15th but found the conditions unsuitable. The British were aware by the afternoon of the 17th that aircraft 7A+LM of 4.(F)/121 had taken off at 07.15 on a reconnaissance of Birmingham and No. 80 Wing discerned “abundant indication” that KGr. 100 was to raise fires for a major attack there that night but failed in the face of poor weather over the Midlands so the target was switched to Southampton (target 55).

The D3R signal was heard by the Y-Service at 15.00 GMT on the 19th; broadcast on 4,500 khz, KGr. 100’s frequency for REGENSCHIRM. As W/C Addison described it, “the leading elements were very successful in starting a very large fire in Birmingham. The succeeding attack was very heavy indeed.” Very little traffic was heard from KGr. 100’s aircraft: five machines were identified and the only communication was a report on the weather over the target.

Nothing more was available from Ultra until the Birmingham raid was underway. Among the decrypts that night were: an order of 13.30 GMT on the 19th regarding the radio frequency for operation REGENSCHIRM; and an instruction from Vannes to WESER and SPREE to operate against target 52 from 16.00–23.00 GMT. The latter was a particularly clear statement of intent but Bletchley in 1940 was not able to decipher Luftwaffe messages fast enough for it to have served as a warning.

Birmingham was bombed again the next night. The Y-Service had picked up the “D3R” signal on 4,500 khz at 15.00 GMT on the 20th and this was taken to indicate that REGENSCHIRM would continue. Ultra too had something to offer but the file only shows that it was issued at some point between 11.00 GMT on the 20th and 01.00 next morning, so it is not possible to say from this source whether it was in time to make a difference. It was learned that ISAR had been told to operate against target 52 “as yesterday” from 16.30–01.00 GMT.

On the 21st orders again went out to WESER and SPREE for operations against target 52 but at 15.10 GMT these were cancelled owing to bad weather. Birmingham was raided once moree on the night of the 22nd/23rd and in these three attacks on the city the Luftwaffe dropped 762 tonnes of high explosive bombs and 1563 incendiary canisters.

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