Virtual Wartime Bletchley Park
by Tony Sale

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Using the Checking Machine

The running of menu text data brfig103.txt revealed a simulator bombe stop of:

w/o: 186
wheel start: RYE
bombe stop: GZT
Steckers: BB DP EY HA OS PD RV VR XQ

Now the modern simulator has actually cheated. It can access all the registers used by the menu and so can print out all the single letters remaining in the registers, the Steckers of the all register letters.

However the real Bombe can only display on its readout the contents of one register, the one to which the input and indicator has been connected.

Thus as the input was connected to 'E' the 'Y' relay would have dropped indicating that for this particular wheel order and wheel positions the Bombe had deduced that E must be Steckered to Y. Given this single piece of information the Checking Machine is now used to deduce the other Steckers for all the register letters used in the menu and thus to validate the stop.

To understand this, take the first link in the menu, E <-> R. In the original cipher/crib pair this encipherment occurred at ZS. The Bombe has deduced that this encipherment actually was E->Y <-> ? ->R i.e. with E steckered to Y, current flowed through the Enigma wheels from input Y to some unknown letter which was steckered to R.

But the Bombe has told us the core wiring position at which this occurs, BUO plus ZZS. The Checking Machine allows us to set up this exact core position and by putting in current at Y, find the core output letter. This letter must be the stecker of R.

So now Run the Checking Machine on this menu.
(Since the Virtual Checking Machine is rather large you might wish to Download this Zip file into a folder, say, \checker, and run the unzipped checkm2.htm in that folder)

On the Checking Sheet the confirmation Steckers, VR and RV were marked with a quote mark and the self-stecker, BB was ringed.

So now try breaking some more difficult menus.

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This page was originally created by the late Tony Sale
the original curator of the Bletchley Park Museum

Virtual Wartime Bletchley Park by Tony Sale

Using the Checking Machine

Virtual Wartime Bletchley Park
by Tony Sale