Saturday, April 17, 2010

Bletchley Park #2

Part 2 of our tour begins when we leave B Block and explore the extensive grounds of Bletchley Park.  This entire complex is always adding exhibits and special programs, some on more diverse subjects such as model railroading. There's a lot to do there, and a lot of opportunities to volunteer.

Pictures of the rather flamboyant mansion house are all over the Internet, and we are about radio here, so a quick Google is recommended for those wishing to see some truly dotty British country architecture.  This neat old place is available for weddings, if you can talk your non-radio-nerd fiancee into it.

Our first photo is of Hut 1. It was built in 1938 or '39 as early wartime operations outgrew the mansion.  As the sign suggests, it once housed radio transmitters, connected to a giant rhombic antenna on the grounds.  This activity was moved away from Bletchley to avoid attracting attention to the site.  Today, Hut 1 houses vintage radio gear from the "Diplomatic Wireless Service," but due to low staffing it is only open weekends.

The low brick wall was added in 1942. It is only a few centimeters from the building, making access to the walls difficult. It was intended as partial protection for the hut, which by then was used for ENIGMA activities.

At a far corner of Bletchley, one comes upon H Block, which is arguably the birthplace of modern computing.  It housed an activity related to attacking German High Command teleprinting traffic, which was on-line encrypted and decrypted at the Baudot bit level with a fearsome multi-rotored mechanical device called the Lorenz machine.  Appropriately, the building is now becoming a British museum of computing.

Geeks won't want to miss H Block.  One wing of it tells the whole story of the Lorenz project.  The next photo shows a recreation of a rather impressive rack from the  dedicated intercept station in Kent. Note the battery of RCA receivers plus two HROs, and associated gear.  These fed the intercepts to an Undulator tape inker for storage and transfer to Bletchley for attempted decryption.

At Bletchley, the encrypted traffic was attacked using a series of increasingly large and sophisticated computing machines.  Early versions were like the "Heath Robinson" machine that's been recreated in this room of H Block:

This line of attack led to the famous Colossus, a true computer using 1500 thermionic valves (radio tubes). Certain features in the Colossus design made it more like modern programmable digital computers than the American ENIAC or other such wartime projects.  Toward the end of the war, 10 of these machines were operational at Bletchley.  All were destroyed for security reasons.

Here's the recreated Colossus Mark 2.

The large frame in the foreground is where the inked tape loops were threaded up and run at a high speed (for the time) past optical readers.  Other racks hold the various parts of the computer.  The black battery of switches was used for manual programming.  A series of counters analyzed the bits for statistical patterns useful for determining the proper wheel settings for decryption.  When the operator got it right, resulting plaintext was printed out by a local teleprinter.

This machine was operating at the time, producing the regular 2-second clicking of relays by which Colossus is known.  You can see some of the clustered tubes all pulsing away.  They don't make any of these tube types any more, so it took some real scrounging to find enough to make this machine go.

This recreation of Colossus has been used several times to decrypt leftover WW II Lorenz text, or newer messages encrypted using Lorenz machines or emulations on the PC.  Again, operator insight is very helpful.  In the right hands, Colossus still performs surprisingly well for this application, with decryption times stacking up fairly well against modern equipment.

Bletchley Park's very comprehensive web site is at .

All photos Copyright © 2010 Hugh Stegman