GPNQHZ987
Type above to decrypt our story...

D-Day: Interception, Intelligence, Invasion

This exhibition will be closed for maintenance on Tuesday 5 and Wednesday 6 November. Thank you for your understanding.

XbTlngpeUZkpL3OVPHcyQke7oyhmbbEh2dLQmDRENXBFj6T5WvLRcuzPzWKsAcWVBDEcS0jROKaqEIRvQ6eVLokBBKFGAOBHKLmp9

r17vezEuQIn59wGRY8RXXXF0wQNAT9rvIbznZZ7D0jdv9AmVle46YAMlyYdD061s1n5MfZ5oYy7vWfA0SXrn0bXlSNy7j2zTHMkG6

b1zVTfB4dyxtCxPGlQZhcd0xFOWz8SOVP3F7upj2O7TAcYfkgoehYLNcSd4UvJAP7C2PjNL6ELILe0uBjITIOw2NpgWAii8Qcx2wT

hJSomSW0IUDA2qAUaoFeCZu0gDjOkhRUUgWCUnXN8PCDsQEofX9ZA6a5M3DCrWNFQyT0xRjnf7IdQ0dzTaqLbbujo2LtQZTWZxt3o

w1rX5Myfdv768YpwX7n2l61XZ5sAliWoJ7zNyNU7d4t1ELjVTupIAOmEbpVgAdEVSAuWxFwrF704aSvCWbrltrKjfgam5Kp7oSaqk

YUaIHw64TDN5JhBwIq4CBSWfd1cRunRGm61CQQEQW9HeTppCX5dslotVlXuxcA11oC6CKoFyejknvN8tpBa7ana86Bn42NTlgQXcs

NyICzGcpPdWpIUWQf21Hp8v88genJGVU3DPT8YGFwf15gK0MKO7OVLqvYrLjczW1bPVcDYyfVzXMziNlQkGuWdcQzTukJs1UL0OZ8

PGTlCnXBlYRg0eHKrWQ81KMMXd2TUYeLy254q3huohlqOfgEC4ANCKnTv4HVHiC7DT4Hbphenu72yL8KX6gLdGVmKSQJEux6m3k0T

8pxcZbqEF7tuA0L8vqqgm2fpLuSQIcbtM3QdUqJ0sJ3nhhEkYgOoD2EFJuuiwMfBgiNdAZY4UXc48MZW0DVNMOtGEC76HoWiDOgML

Aae22cLUVvMVb93gQd6deYnTdYO7ViEH8wjvCtU3RQpcIa9CchYBhZ4ztFdTVDUSre6s51nkA7SiiTzAcyLlljV2ixRGraRR5PHMf

2k2wSqhowKbij31mOh33Fe5M135CCWu6uGJUprciYHb5yYT34AMls0LU23grG5MdiQbuGiAmeDjnpHjuutQetX5QkHsFmLOMDFtpm

DdT2P8QjaAf9jO2MruSA4QPTcDJPuan7aKYdJtdnxHgiap3FzQDkRNPYByqNHpwi2pqqw1oXQYa0igzQMBWzbMWZOKM4wdZ3FVLnc

PqQuJbMoq0KUFnYSXjRI9po4AjNwfyctmAiCAWWLi8k6OIuT8QlBjgmveJ5UaPwahLj16kKdVcmwioBzq5734JObRwY7vNzPKbXN4

rcf3WaUoXWghvl68iPcXtqdQsZTG2r2Uddzi07iiamhKv69IQnh4WhAoNrCAYoNTf8b7e2dE3XVhmBeLgFzypjPgLsEkU9twwCGql

tCk9Rxos1Gl24XmXzUtMZIiG7XZz1w5EmHMk9nwblGxy97obbt1Y5ZCTtOLOXeiVlFZeIP1cr2KAmtiFVSDmtjhvMqWyYGoR1w9E4

ErRszvzeHqERiyi32flCMHA77R5QOJOR1X64sx9OQOAqPmeAkUz5kqGE1Bp9aHDgpnbM0apEMRy1zehVoCZJNI5vOeB8fXHTHS4bE

XWD0YHoW3os9zOQYfbJBUKUqewm9gpHFdsPj87VCGH6BKJ5ZR14DAIUFLEXN2TQPWTE3dhleuofWTg72UpgqrmiA4AOC99vxhHHZA

aEXV4lHyhW9ODsvGe6fXFbuHdG8ufHFbJhbsVkWAaypANoKIdCa8pt0RD2vImkpmJkm1JBmtUCGe1yyvL4LARWUP15RfpntUp07WU

xiT7VXtaiYFrPG5GexbusRd1Nn49moTieJ1ZFmEDCxg4KCRipggXTwnsSFgZwIdNet3wlZZwsLYhABwG3wuKclhNRtIzsMiCBcTPm

a0Fq0tVpjnQS4XkiNAfxXUGENHFQPtTf7qty5JddtV8Nqay85L17qt0TnF0bmEv8geK09ySCPRo2gE9otdWhHATUMiiYNHNtJLAiE

2CYGwv8gVkxsZV6dWGfrgx9j0vMK6CjGryozpAXrorB8lmT0goMALy1u2LaPomowv3iiS2IhWrmrieKSg5fmEcSOsNhLVrlrQAfEN

Kyywpg6qmdJKELUA4O6RDaXyusnddrIkh4hv1JXbTT9mK20iYccA8FRt7yWX2KJrBASBK86VMRVUW88bKKSyIDkzvuv9rl3LptGke

rylWHrZ7wYUNqLOW8UtcvAjS2dkX0O9eZvXTRM5ONe4hlfycON60vIxOjULUHqKSDW75j8C0W4y9ffOBgIkC5tebAYTDLbqNGp1pz

qPRPYg6em7DpDkHPIxfEQJSfoKjX7HtKnXIb7zuDMOJHjw6oyWCGrmOxaTvaHxorcY4PyqYcbB3QN5MjQoWlRsMDN5CI3dcfCrWcE

FTAEjzVEwiMOaRiiPquXeqSwjQ3vy5WHmMuP0dRr0QZKU4AR0yDE3je1IK54HmYnigNIMsCyUAl8xlQ8LtTQpMkUAje8kygEFAKwi

Xxc5nek4eYafP0zGkbmCzTsVuD3VHdArFjrJLNYVKgnfLW2ckZwGiaoy4S6NhWw33wRVgnmgEiiKFtiefCS4AImriUme6PbUiDjFm

XboxngpeUZkpL3OVPHcyQke7oyhmbbEh2dLQmDRENXBFj6T5WvLRcuzPzWKscWVBDEcS0jROKaqEIRvQ6eVLAokBBKFGAOBHKLmp9

ErPIisLYgRJ8IR2u7QOMxGNi6k6hs9tOWth3OM6TC0rOTQfvpz6IIzVTXBEQomQl1kWVcPwTqv2gdmTa6dC9x2PaS4qmqS5txyXer

SnYSsxGG6oebPBiGg5X0tMEsypWRYNu7bxfBvixZfRpFCBKnHSwtYb0vecLKHnvCC1OJsUOy5Skrf5XDzVYMdcCMxBhOxsv3iB5jR

XWD0YHoW3os9zOQYfbJBUKUqewm9gpHFdsPjibNYXDtFnO59Mur84fTkoy0IiYCdTE3dhleuofWTg72UpgqrmiAL4AOC99vxhHHZA

QOlal5GQaui90qp0Xm63jXnKGXbnDaeVuWh6SeNbh6Z52AL8wRmNrLKV9hlUYrPNK8QEmYDUciLoTkill6CPCbvtE5zdlRo1iQPS9

r17vezEuQIn59wGRY8RXXXF0wQNAT9rvIbznZZ7D0jdv9AmVle46YAMlyYdD01s1n5MfZ5oYy7vWfA0SXrn0bXlSNAy7j2zTHMkG6

1zVTfB4dyxtCxPGlQZhcd0xFOWz8SOVP3F7upj2O7TAcYfkgoehYLNcSd4UvJP7C2PjNL6ELILe0uBjITIOw2NpgWAWii8Qcx2wTA

01
/
From September 1940, Bletchley Park’s decryption of the German Luftwaffe (Air Force) ‘Brown’ Enigma key played a crucial part in protecting the UK during the Battle of Britain and the Blitz. Brown was used by the German Air Force’s radio and research regiment. In 1940, they were responsible for two beam navigation systems used by the Luftwaffe to direct their night bombing raids over Britain. Brown messages gave valuable information about the systems, allowing the British to jam navigational beams and divert German bombers away from their targets. They also helped identify the target for each night’s raid – if Hut 6 was able to decrypt the messages in time. But the Brown network contained more information than could be read in the messages themselves. Traffic analysis at Y (wireless intercept) stations listening to Brown traffic built up a detailed picture of German navigation beam operations, from transmitter locations to operational information.

 

This album was first published on 14 September 2020.

The ‘Note on the Brown Group’, dated 24 December 1940, was compiled by staff at Chatham, then home of the principal Army Y (wireless intercept) Station. This station was the first to intercept the Luftwaffe’s Red Enigma key and by late 1940 was also intercepting Brown. The Note shows how much information Chatham was able to deduce from traffic analysis on Brown messages during the Battle of Britain and the Blitz.

As a Y Station, Chatham would have access to all the unencrypted parts of intercepted messages as well as frequencies, call-signs and operator chat – all useful information for traffic analysis. However the document, marked ‘Secret’, also shows the compartmentalisation of knowledge between Bletchley Park and Chatham. The compiler of the Note had no access to the encrypted texts of the messages, which were read only at Bletchley Park, or to the intelligence derived from those texts.

Chatham observed that the Vannes station was using both the Brown and Red Enigma keys, which was unusual. Other transmission stations using Brown did not also use Red. Vannes was the home of KG100, the Luftwaffe pathfinder bomber squadron which was responsible for leading beam-directed raids on the UK. As an active bomber base, Vannes would have needed to communicate on Red for normal administration as well as on Brown for beam navigation.

The station at ‘LEIPZIG Area’ refers to Köthen, near Liepzig in Germany. This was the location of the HQ of the Luftwaffe Nachtrichten Versuchs Regiment (the Air Force radio and research regiment).

A peak of activity in the early afternoon (1200 – 1400 GMT) matches the times when raids were being prepared for that evening. Operational information, such as navigational beam angles for that night’s target, would be communicated to German bomber units.

The locations of Brown key users identified by Chatham include ‘VANNES, MORLAIX, CHERBOURG, BOULOGNE, TEXEL’. These correspond with the base of the KG100 pathfinder squadron, and other bases that transmitted the navigational beams for bomber units to follow during raids.

The security of the Brown Enigma network was notoriously bad, according to the History of Hut 6 – giving the codebreakers and traffic analysts a helping hand. As an experimental, secret unit, Brown operators were not subject to the usual scrutiny applied to Luftwaffe signals regiments and were also mostly personal friends. Plain language chat was common, as were basic security breaches such as repeatedly using their own initials as Enigma rotor settings.

Chatham notes that the three-letter group ‘FDL’ interpreted as Feindlich (Enemy), is associated with certain call signs and frequencies. This may be a reference to British efforts to jam the various navigational beam systems.

The German beam navigation systems used during night raids in late 1940 were codenamed Knickebein and X-Gerät – likely the XBT identified in this section of the Note. Antennae on the French, Dutch and Norwegian coasts transmitted navigational beams across the UK. These guided bombers to their targets, pinpointed by the intersection of two beams. The longer-range X-Gerät system also used beam intersections to tell aircrews when to release their bombs for maximum accuracy.

Chatham had also identified aircraft movements and callsigns in the Brown messages – particularly when operators bypassed security measures by sending unencrypted messages over the network. The callsigns probably refer to aircraft in KG100 squadron, which led flying operations based on the beams.

Related articles