Part 13: Bletchley Park and the Enigma


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With the success of the recent movie "The Imitation Game" most people are familiar with the Enigma cipher machine and its critical role in WWII.  The Germans used the cipher with great success to hide the positions of their submarines and take a heavy toll on Allied cargo traffic.  Had the Enigma code not been cracked by the British team (led by Alan Turing) it is possible that the war might have gone the other direction.  The facility that headed the code cracking is located at Bletchley Park northwest of London, about an hour away by light rail.

The Photos

The photos below are what we saw.

Along the Fleet Street path to the tube station, we passed these great griffin terra cotta statues on an old bank building.  Sub Hoc Floresco roughly means  "under this I flourish".

Despite an attractive seat mate, Steve looks solemn.

Bletchley Park was 2 tube rides and one train ride away from central London.  There was a large museum that spanned 2 buildings and a set of outbuildings that housed smaller exhibits.  The key aspect (if you will excuse the pun) of the this class of cipher machine is the concept of a mapping rotor.  Most machines use multiple rotors and more rotors mean a higher complexity ("stronger") cipher. A single rotor permutes a set of characters into another set, but in a known fixed way.  When multiple rotors are used, the input set is mapped by the first rotor and then the output of the mapping is mapped again by the second rotor and so on.  The power of the machine was that the position of the rotors changed after each character as mapped greatly increasing the difficulty of breaking the cipher.  Usually, there were multiple rotors to choose from, say 3 out of a set of 8.  Each rotor's wiring contains a different mapping.  Wikipedia has a nice writeup on Enigma and even NSA's historian has written a paper about the German's machines.

To crack a cipher, you must first have messages to work on, so Bletchley's past was very much associated with radios.  The intercepted messages were in morse code over radio and civilian ham radio operators were drafted to be "listeners" of the code traffic.  Early radios were made using vacuum tubes, called "valves" by the Brits.  These valves came in all sizes and shapes with varying degrees of complexity.  This exhibit shows a sample of some of the diverse valves used in radios of the era.

The "Mansion" at BP was on the grounds when they were purchased by the crown for wartime activities.  This estate had beautiful grounds and a small lake.

The out buildings, built later, housed the actual work efforts.  Some of the early structures were mere shacks referred to as "huts".

This swan was enjoying his breakfast in the shallow waters of the pond.

May is early spring in England and some of the trees were sporting glorious blooms.  Others were throwing off mountains of pollen that had us sneezing like crazy.

The Mansion served in a number of roles at Bletchley including the commander's HQ, canteen and mess hall.  And, the building served as the filming set for "The Imitation Game".

The entrance to the mansion had this plaque from the American IEEE.

Alan Turing and his team designed an electro-mechanical machine called the "bombe" that was used to test key hypotheses in parallel.  Motors turned shafts that turned rotors.  Very complex, very intricate, very ingenious and very successful.  This was used as a prop in the movie but was not capable of actually solving a cipher.

The machine consisted of relay logic and lots and lots of discrete wires.

There was a small period vehicle display area.

It was not clear if this nice Packard was ever actually in service at Bletchley.

Back in the main museum there were examples of cipher machines.  This one, called the Lorenz, was designated the SZ-42 and had 12 rotors.

The Lorenz was part of a cryptographic teletype system used by the German high command.

This bombe machine, named "Phoenix" because it was re-built from raw parts stored after the war is functional.  The operation was demonstrated and just as described in a number of the exhibits, it was noisy.

The rotor dials are driven by geared shafts behind the front panel.  Every 24 rotations of an upper rotor produces a single position change on the rotor below.

This is an electromechanical assembly and therefore is subject to friction.  Friction requires some kind of lubrication, usually oil.  The oil is delivered using a copper tube plumbing system dripping oil on the worm gears.

The plug panel provides the programmability of the Bombe.  Wiring changes were done when a new day's code was being cracked.  Changes were performed each day.

The inner wiring of the bombe rotors was quite a rat's nest and required special fixtures to assemble and test.

The local rail infrastructure is impressive.  Plenty of tracks and plenty of above-ground wiring.  Note the nest of wires above.

Back in the Fleet Street area, the sun was out (sorta) and allowed a photo of the Royal Courts of Justice building.

I did not realize until I uploaded photos that I did not get a single photo of an actual Enigma machine, but these are available on the web.  Bletchley Park was very interesting and we could have easily spent more time in the main museum.  But, as it was, we burned a whole day there including travel to and from the facility.

This was our last day in London.  We ate at a trendy asian restaurant and headed back to the hotel to pack.  Tomorrow is a travel day: a train to Scotland.

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