The US 6812 Division Bombe Report Eastcote 1944 Page 20

Tony Sale's Codes and Ciphers

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- 15 - TOP SECRET-T


The checker must go round every closure to ascertain that the stecker
returns to the original letter. Thus:


When starting with P/O, getting Q/T, M/S, we must be able to set ZZA, press S and light up 0. Having completed the closure the last letter, S in this case, should be marked with a check mark to indicate that you have made this closure.


Check all steckers against alphabet at the tope of the sheet and mark
confirmation and self steckers, as follows:

A/P "
P/A "
S/(S)


All entries onto subsidiary chain must be checked. When checking
subsidiary chain all entries back onto the main chain must result in
a confirmation, otherwise there is an illegal contradiction and the
stop is wrong. Check over steckers and mark legal contradictions as
follows:

R/W*
T/W


Summarize the total number of self steckers, legal contradictions,
and confirmations for the stop and write the total in the stecker
column. Thus:

2 *
1 "
(2)



CHECK STOPS

In order to maintain a continuous check on the performance of

the bombe and its operator, check stops are taken on all wheel orders
where a good stop does not occur. This is done by opening a link
through removing the fast drum. Always try to open a "female" or the
smallest closure. If, however, there is no closure, an outlying link
can be taken off. In any case the link being broken must be one or
more links removed from the input.
The stop slip which the operator gives the checker will bear the
notation that a link was removed to obtain the stop, shown as minus
the link setting, that is (-ZZA). All other links on the menu are
checked in the normal manner. The notation (-ZZA) is placed in the
same square with the wheel order and letters of the stop. If the
link removed is an outlying link, an illegal contradiction must be
obtained from the stecker of the letter at the end of the removed
link. If the link removed breaks a closure, the checker must check
across the link removed and prove that it fails the closure as it
should. If these results are not obtained the check stop is wrong.
When checking across a link that was removed to break a closure write
down the resulting incorrect stecker in the upper left corner of the
square and put the correct stecker in the lower right corner of the
square.


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