The work carried
out at Bletchley Park was of immense importance to the war effort and, as such,
was extremely top-secret. It seems that none of those involved squealed about
the important breakthroughs, and the Germans remained unaware that every message
they transmitted via the Enigma was being deciphered and read by the British.
Towards the end of the war, a common joke among top-level intelligence staff
was that if Hitler wanted any information about the movements of his admiralty,
he need only ask the British, who knew more about German naval movements than
the Germans themselves!
Winston Churchill
famously referred to the workers at Bletchley Park as “my geese that laid the
golden egg and never cackled”. The work at Bletchley Park was so secretive that
details of the important codebreaking carried out there were not made public until
the 1970s. And important it was: the intelligence produced at BP was so crucial
to the Allied war effort it has been said that without this, the war may have
been up to two years longer (some believe it may have been up to 4 years
longer).
Enigma
 |
We saw these Enigma machines in the Science Museum in London.
It was an exhibit on Alan Turing, one of the brains at BP. |
In the early 1920s,
a German engineer was having much success with his machine that could code and
transmit secure information, the Enigma machine. Enigma used electrical
connections to encrypt messages, and so the process was much quicker than it
had been when an operator had needed to perform encryption by hand, using a
table of codes. Most importantly, the resulting encrypted messages were
considered impossible to crack. For this reason, by 1933, all of the German
armed forces were using their own variants of the Enigma.
An Enigma machine
looks like a typewriter, but with some extra features. The operator types in
their message, then the machine uses three to five rotors (depending on the
version of the machine) to scramble the text and produce different letters of
the alphabet. This is known as a substitution cypher, as one letter is
substituted for another. The receiver of the message needs to know the exact
settings of the rotors in order to reconstitute the text. Over the years the
basic machine became more complicated as more rotors were added and as German
code experts added plugs with electronic circuits.
One key point of
difference with the Enigma is that when an operator inputs a letter, that
letter will never be enciphered as itself. That is the weakness that
eventually enabled the machine’s codes to be ‘cracked’. There were certain
words that would generally appear in a message, for example ‘to’ at the start,
and yet the letters from those words never appeared in the encrypted
messages.
By 1932, the
Polish had managed to decipher Enigma messages. At that stage, the cypher was
only altered every few months, but as the 1930s rolled on and German military
operations began to increase in frequency, so did the number of messages being
transmitted. It wasn’t long before the cypher was being changed at least once
per day. This gave 159 million million million possible settings to choose
from! It is no wonder the Germans considered the machine to be
unbreakable.
As the
encryption became more complicated, the Poles were unable to continue
deciphering the messages. In 1939, they handed their data to the British, and
Bletchley Park became the new centre for efforts to decrypt the Enigma.
The first
break into Enigma came in January 1940, when a team worked out the key used by
the German Army. Soon after, they also unravelled the key used by Luftwaffe
officers who coordinated air support for army units. BP staff based in a
neighbouring hut turned the deciphered messages – known as Ultra - into
intelligence reports. As the cracking of Enigma was extremely top-secret, the
resulting reports were made to look like they had been produced by an MI6 spy,
codenamed Boniface, with a network of imaginary agents inside Germany.
At this
stage, there were some amazing minds working at BP. Dilly Knox, Alan Turing,
Gordan Welchman, and Max Newman knew that deciphering Enigma messages by hand
was taking too much time. By the time the messages were unravelled, the
intelligence was of little operational use. Alan Turing, with the support of
the others, created a device that would run through all possible Enigma wheel
configurations, in order to reduce the possible number of settings that could
have been used to encrypt the message. This reduced the amount of codebreaking
work that had to be done by hand. The machines were known as Bombes, and were
generally operated by Wrens, members of the Women’s Royal Naval Service.
(Unfortunately we
couldn't get any pictures of a Bombe, as that part of BP was closed for
renovations. You can find a picture of it here: http://www.theregister.co.uk/2009/03/23/bletchley_bombe/)
The resulting
intelligence – Ultra – was extremely valuable to the Allies. Throughout
the First Battle of the Atlantic, Ultra gave the navy vital information about
the positions of German submarine packs (‘wolfpacks’) and the Admiralty was
able to fight off the U-Boats which attacked merchant ships bringing supplies
to Britain from North America. Ultra also enabled the Allies to discover if the
Germans had swallowed deception plans they had planted, such as those for the
invasion of Sicily in July 1943. Before the operation, secret agents planted
false intelligence suggesting that plans to attack Sicily were only a ruse, and
that real landings would take place elsewhere. Ultra revealed that
the Germans had fallen for the false intelligence and believed an Allied
operation in Sicily would only be a ruse for real attacks elsewhere. The
resulting invasion of Sicily was a success, and was one of the main turning
points in the war. Ultra also played a key role in the success of the D-Day
landings in June 1944. Ultra intercepts showed that the Germans had believed
the deception campaigns, and were convinced a landing was to be made in the Pas
de Calais. This meant that when the eventual landings took place in Normandy,
and over 150,000 Allied troops arrived by air and sea, German resistance was
low and the Allies were able to finally re-gain a foothold in
Europe. Right to the end of the war, the Germans did not believe that the
Enigma had been broken and they continued to send sensitive information which
was promptly deciphered by a select few at BP.
Lorenz
Another triumph of Bletchley Park was the
deciphering of messages sent using a Lorenz cypher. Before the war, the High
Command of the Germany Army had requested the construction of a teleprinter
cypher machine that would enable them to send secret messages via radio. The
Lorenz Company designed a machine that featured up to twelve wheels all with a
different number of cams, or pins, in them. From here, it all gets a bit
complicated for me, but I understand that this means the possible encoding
options are huge. (Wikipedia it or use Tony Sale’s amazing website - http://www.codesandciphers.org.uk/index.htm - if you want to
know more: )
The Lorenz machine
used a combination of dots and crosses and Boolean 0s and 1s to print a
message. It then used the Vernam system of adding a random set of obscuring
characters before transmitting the message. At the receiving end, the random
set of obscuring characters would be added back on to the message, they would
cancel themselves out, and the original message characters could then be
printed. This cypher system, which uses one-time purely random obscuring
characters, is unbreakable. Until you factor in human error.
On August 30, 1941,
the Germans made a terrible mistake. An operator had a long message of
nearly 4,000 characters to be sent from one part of the German Army High
command to another. He set up his Lorenz machine, sent a twelve letter indicator
to the receiving operator – this would tell the receiver which settings to put
onto his Lorenz machine - and keyed in his long message. The receiving operator
then signalled that he had not received the message and to send it again. Both
operators then put their Lorenz machines in the same start position
they had used for the original message – even though this was
forbidden. The second time around, the sending operator made some abbreviations
and mistakes. The interceptors at Knockholt realised that the same message was
coming through, as it was using the same one-time obscuring sequence. However,
the message was slightly different and this set off alarm bells. The incoming
text was quickly sent to Bletchley Park, where one of the top codebreakers, John
Tiltman began to study it.
Eventually
Tiltman was able to work out a chunk of the obscuring character sequence that
the cipher machine generated. After three months, his team had failed to make
any further headway, and 24 year old mathematician Bill Tutte was brought in.
In two months, Tutte worked out the complete logical structure of the cypher
machine. Without ever seeing a Lorenz machine (in fact, the British would not
come face-to-face with one until 1945), Tutte managed to reverse engineer the cypher
machine. This was a huge breakthrough, possibly one of the greatest
intellectual feats of the War.
Soon, the team had
constructed a machine, known as the Tunny, using Tutte’s calculations. Further
developments produced a family of machines known as the Robinsons, though these
were still too slow to be of much use to the war effort. It was time to call in the
big(ger) guns.
Above,
Tunny and Heath Robinson machines
Max Newman, a
mathematician, and his engineer sidekick Tommy Flowers soon designed and
constructed THE COLOSSUS. (*Cue dramatic music*) The Germans enciphered a
message with the Lorenz, transmitted it by radio, when it was intercepted and
recorded on to paper tape at BP. The tape was joined into a loop with special
punched holes at the beginning and end of the text. Colossus was able to read
the tape at 5,000 characters per second.
(For computer geeks, “At 5,000 cps the interval
between sprocket holes is 200 microseconds. In this time Colossus will do up to
100 Boolean calculations simultaneously on each of the five tape channels and
across a five character matrix. The gate delay time is 1.2 microseconds. Colossus
is so fast and parallel that a modern PC programmed to do the same
code-breaking task takes as long as Colossus to achieve a result.” According to
Tony Sale, the former curator at BP.)
By Christmas 1943,
a Mark 1 Colossus was assembled at Bletchley. The machine could
break Lorenz messages in hours, which was a huge advance. It was just in
time to decipher messages related to D-Day, and the resulting deciphered
messages revealed that Hitler had fallen for the deception campaigns (such as
the phantom army in the south of England, phantom convoys moving across the
Channel – look it up, it’s very exciting stuff!) and was convinced that an
attack would be launched on the Calais area of northern France, rather than at the correct location of Normandy. This was
extremely valuable knowledge to possess, and it was all thanks to the
hardworking teams at Bletchley Park.
By the end of the war, nine more
Colossuses (Colossi?) had been built, and 63 million characters of German
messages had been decrypted.
Knockholt
While we were in
the Computing Museum, we were excited to come across some information about
Knockholt. Knockholt is our neighbouring village, and in it sits a large
farm house called Ivy Farm. This house was recently for sale at £1.25 million,
and it hides an exciting past.
During WW2, Ivy
Farm was requisitioned by GC&CS and was used as a wireless intercept
station. There was a wireless room at BP, but concerns around German detection
of the site soon dictated that other stations should be created in numerous
locations throughout the United Kingdom. One of the most important of these was
at Ivy Farm in Knockholt. The Farm served as a Radio Intercept Station for
messages transmitted by means other than Morse Code, e.g. such as those that
had been enciphered using the Lorenz.
The 815 workers
were either billeted to families in surrounding villages, or accommodated in
huts built on the land around Ivy Farm. From November 1942 to May 1945,
the Knockholt staff worked tirelessly, collecting 167,727 messages, of which
27,631 were sent to Bletchly Park where 13,508 were successfully
deciphered.
Isn't that
exciting?! Living just minutes from one of Britain's most important
intelligence locations of WW2?
