Introduction
Extract from the US 6812 Bombe Report:
The Bombe contains the equivalent of the wheels, uncle walters, current input and stecker arrangements of 36 enigma machines and is motor driver.
Tthe front of the bombe
On the front of the bombe are three banks of enigma wheels, 12 enigmas to a bank, and 3 wheels to an enigma. The middle bank also include three indicator wheels which read the relative ringstellung position at any point in the run.
The drums have colors that correspond to the number of the corresponding rotor:
- I (1) – Red
- II (2) – Maroon
- III (3) – Green
- IV (4) – Yellow
- V (5) – Light Brown
- VI (6) – Blue
- VII (7) – Black
- VIII (8) – Silver
The rear of the bombe
On the rear of the machine are found the jacks on which the menu is plugged. Three columns jacks serve one bank of enigmas, the left hand set of three columns serve the top bank of enigmas, the middle set of three columns serve the middle of enigmas, ...
The sides of the bombe
On the right side of the bombe are found the searching keys and also the relay indicator which reads the stecker of the input letter for any stop.
Three uncle walters are located on the left side of the bombe. The right hand uncle walter serves the top bank of enigmas, the middle uncle walter the middle bank of enigma, … The uncle walter and the diagonal board remains fixed, and the wheels are rotated through all possible positions.
Working
The bombe is designed to try simultaneously 26 steckers of the input letter on as many enigmas as there are possible pairs leading to steckers (indicated by the crib). The test of 26 possible steckers is made at each position of the wheels. The wheels are advanced through 17,576 positions in each run. Each enigma has the same wheel order and is set to a starting position which bears the same relation to ZZZ that the actual machine bore to its “starting point”.
Diagonal board
The DIAGONAL BOARD is made up of 26 jacks of 26 contacts each, representing all possible steckering of each letter to itself and each other letter. The purpose of the board is to ensure that all steckers obtained are legal (good), conforming to the characteristics of the German machine and that no illegal contradictions (bad steckers) are show. The diagonal board is arranged so that all recpiprocals are permamently wired together i.e. if A is connected to f the F is connected to a. When encoding on the German machine current is present on only one out of 26 possible circuits. Conversely a correct stecker will be obtained on the bombe when the diagonal board has only one set of contacts (a “straight”) without current – current is on all other 25 circuits.