A Visit to Bletchley Park

Matthew and I arrived in Milton Keynes on Saturday afternoon around 3.30.
As we had missed lunch, we found a local pub, appropriately named the
Enigma Tavern. We were pleasantly surprised at the low prices. We had
two reasonable meals for about £7.50 each.

We knew we were on the right side of MK for our accommodation which was a village pub about 4 miles from BP. Getting out of MK in the right
direction proved challenging. (I must get a new GPS.) Eventually we
headed ìn the right direction and found the village. Again the pub meal
prices were very good as we decided to have another meal about 8.30.
The locals in the bar were also very friendly.

Around 10am the next day we set off for BP. We got our tickets and the
brochure. Fortunately it was quite quiet. The main displays are located
in Block B which featured a number of original models of Enigma machines,
as well as Mussolini's encrypting device. One of the guides had just
started a demonstration of a working 3-wheel Enigma, which was
fascinating to watch.

As this finished he was followed by a demonstration of a replica Bombe,
which was shown providing possible solutions to daily Enigma machine
settings for real messages intercepted at Y-stations in WW2. The Bombe
acts as 36 enigma machines running in parallel, to rule out incorrect key
settings. It was all built around authentic Post Office relays (still in
use on our computer Block Switching Chassis at the power station). The
basis of the Bombe is having an identified Crib message, from which a
"menu" is formed . The crib is a predictable message such as "Nothing to
report". Having spent about 30 minutes quizzing the guides, I feel I
have just scratched the surface of the Bombe techniques used at BP for
the breaking of cyphers.

We then moved on to some of the other Blocks and huts, many of which are still being renovated. Hut 6 was used for decrypting German Army and Air Force messages. A special chute was devised to send the messages to hut 3. This was so that each unit would not know what techniques the other was using. Hut 3 would then translate and analyse the plain language messages passed to them. Each decrypted message (known as Ultra) was written as if it had come from an agent in the field, to disguise the fact that they had been decrypted from the original intercepted Enigma transmissions.

The whole process of Enigma decryption was taking place at BP on an
industrial scale, for once the settings for the day were obtained, all
messages intercepted on that particular network could be decoded from
midnight until midnight the next day

We then went to the National Radio Centre on the site. We were met by a
local radio amateur after which we undertook the short journey around the
exhibits. They were well thought out, but a guide would have been useful
for demonstrating to the public each of the interactive exhibits, which
were gain, modulation, detection etc. We then reached the end of the
short set of exhibits to find the GB2RS station operating on 17m. The
bands seemed OK as he was just working a JA on the beam. The station was very professional-looking , but I could not help thinking that it would
have been good to also have a much simpler station on show. Anyone
thinking of taking up the hobby would probably have been put off by the
expensive array of computers, transceivers and displays making up the
station.

We then made our way to some of the other huts including one featuring
the role of homing pigeons during the two world wars. Another hut featured
radios used by the Diplomatic service. Yet another hut had been used by
Ian Flemming (007 fame) and had been kitted out with items showing his
involvement at BP. Around 3.30 we were treated to a very low level
flypass of a Dakota; a part of the Battle of Britain Memorial team.
By 5.00 we had seen most of the site, but not the separate exhibitions
of Colossus, and the National Computing Museum.

We returned the next day (tickets are valid for one year) in order to
see the remaining items. We found out that the Computing Museum does
not open till 1pm. The decision was made to book on a tour in order to
get a better overall feel for the activties which had taken place on the
site around WW2.

This was well worthwhile and finished around midday. The hut housing the
re-built Colossus was now open, so we paid it a visit. This machine was
used to decode the very high grade messages encrypted on the 12-wheel
Lorenz machines used by Hitler and other senior German figures.

The Lorenz machines generated RTTY messages directly, which were
encrypted using binary addition of a key. The same binary addition was
applied at the receiving end which then restores the original message.

After a severe security lapse by a German operative, in which the same
message was resent using the same key and settings, but with abreviated
text; a mathematician was able to determine the number, wiring and use
of the 12 wheels despite never having seen such a device.

Colossus was built using several thousand valves, of which it was said
that it would be unreliable. Designer Tommy Flowers proved otherwise,
as he knew the machines would be running 24 X 7, thus significantly
improving their reliability. (The re-built Colossus has a failure rate
of about 5 valves per year - the equates to a MTBF of 10 weeks).

The Colossus acted as a semi-programmable parallel computer. This
computer, the world's first, used parallel processing techniques such
that only a modern dual core processor is able to achieve anywhere
near the same speeds.

After this we spent a couple of hours in the National Computing Museum.
Just about every computer system I have ever worked on was represented
here, from ICL 2900 mainframes to PDP-8's & 11s and Ferranti Argus
computers as still used in Heysham power station. We also saw the
amazing "WITCH" computer in action. This is the worlds oldest original
computer system still working. You can read the instruction codes and
data directly from the store as it is all visible.

One of the best displays was of the old West Drayton Air Traffic Control
system. A friend of mine (Eddie Richardson, the original owner of Walton
Radar Systems) had designed this PDP-11 based system to enable for the
first time, the recording and replay of ATC data. The system was
re-running in real-time the actual ATC displays from West Drayton some
20 years ago.

We eventually got away from BP around 3.30. Apologies for such a long
post, but hopefully it conveys some of the wonder of yesteryear. If
you get the chance to visit BP, then I would highly recommend it. There
is still a lot more renovation work to be completed, so I will try to
make a return visit in about 2 to 3 years.

It was fascinating to wander around the BP site knowing that the fate
of the entire world once lay in the hands of the dedicated scientists
and cryptologists who worked in total secrecy before, during and also
after WW2.

Andrew, G0LWU