Asylum Models and Effects

This is the company who were subcontracted to build the six ‘props’ Bombes. They are located in South London where they have very advanced facilities available. They tackle almost anything.

For example, if one looks at the photograph below one will just see at the top a giraffe’s head and neck. This is fully motorised and extremely lifelike when operated.

Three “Props” Bombes in an early state of construction 

There are many components that can be described but let us just concentrate, as a typical example, on the drums or Brush Holder Assemblies as BTM described them. It was never planned to show commutators or the brush side of the drums. However, the outside face was intended to be made as accurately as possible. What would have originally been a brass cover was made out of MDF turned on Asylum’s CNC machine. Around 700 drums were made in total.

For the rest of the drum components, our AutoCAD drawings were used. The engraved indicator discs and the drum clips were made by Asylum exactly to drawing. They took our files, converted them into.DXF format and after a small amount of extra work fed these into the CNC machine. We were then able to use some of the surplus parts on the rebuild. Other parts were made by manufacturing a small number of parts from our drawings and then using these as patterns to mould larger numbers in a form of plastic.

REAR OF MOCK UP It is amazing how much time and effort is wasted in the Movie Industry. In our case vast amounts of Asylum effort went into making an accurate rear on one of the Bombes and then it was not shown. The rear of the machine, as most people will know, is where the Jack Frame is located. Here menus are plugged up using plaited cables and cross and connect units. In the photo below can be seen the top right area of the connectors. The layout of the connectors is in columns. To the left is a diagonal board, the next is made up of groups of connecting areas. To the right are the input and output jacks of 12 Letchworth Enigmas. This whole arrangement is then repeated three times to cover the 3 banks and 36 Enigmas. In all 228 jacks are fitted each having 26 contacts. This makes a total of 5928 contacts. Asylum wished to get as close as possible to real jacks but could not locate enough using their own sources. Around 130 were found in Wales and were kindly donated by Mr. John Griffiths. These were the early type which we particularly wanted for the rebuild so a trade was made where we provided 228 of a slightly later type in exchange for the 130. Whichever version was used they still had to be cut down from 36 to 26 way. Asylum stripped out the 228, shortened them, painted them as appropriate and reassembled the 5928 contacts. These were then mounted on side angles as in the original. The only detail not quite correct is that lead in / locating slots for the jacks have not been cut.<We consider it a great pity that this excellent part of the mock-up did not appear in the movie but at least we did have it on display at Bletchley Park.


Not all the drawings we created were of direct benefit to the Rebuild proper. One example being the plugboard drawings. Three BTM style plugboards are fitted to the left-hand end of the machine. These represent the ‘Uncle Walters’ of a German Enigma machine. On the real machine, these are mounted on the inner frame and the covers fit around them with only the front section protruding beyond the cover line. Asylum did not want to cut into their ‘boxes’ so we provided a special drawing of just the protruding section. These were made very accurately by Asylum and attached to the plain left-hand face of the ‘box’. The result is a left-hand end, which is very difficult to distinguish from the real thing. Please see below.

(Incidentally, in this photo above we are showing “A” type (Apple) plugboards). This plugging was rarely used. However, if we consider the plot of the movie, the Bombes were being used to find the settings of ‘U’ boat navy 4 wheel Enigma machines. Maybe we should not question this too much because here we are into the realms of fiction. Perhaps however a discussion might take place on how this break could have been successful when there were no true 4 wheel Bombes in existence!) INDICATOR UNIT A “real” indicator unit without covers may be seen”/indunit1/ The area around the indicator unit and bail lever was difficult to reproduce accurately but we succeeded by adding appropriate covers to the known units underneath and by studying photographs in detail. In the film you might see a WRNS peering into this unit whilst the machine is running. We do not see the point in this part of the filming. There would be nothing to see except all the “toggles” in their “off” position. If this were not the case then the machine would have already stopped. This would then be the time to see which “toggles” were tripped!

Activity at Bletchley Park after Delivery


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