called a menu and was in fact a crib in diagram form. If the crib and cypher text were
E T R B H U S E D F S H J U Q A P L
V V V J V O N D E R G R O E B E N J
the bombe would he asked to find a position on the machine where V would encypher as E, followed at the next position by V encyphering as T etc. To perform this function for one wheel order the bombe would take about 20 minutes, the wheel order would then be changed and the process repeated.
The bombe was a highly complicated electrical apparatus, involving some 10 miles of wire and about 1 million soldered connections. Its intricate and delicate apparatus had to be kept in perfect condition or the right answer was likely to be missed. An embryonic bombe was evolved by the Poles and could be used on the comparatively simple pre-war enigma problems. The invention of the bombe as we have known it was largely the work of Turing, Welchman, and, on the technical side, Keen.
Unfortunately the bombe was an expensive apparatus and it was far from certain that it would work or, even if the bombe itself worked, that it would enable us to break Enigma. Its original production, and above all the acceptance of a scheme for large scale production, was the subject of long and bitter battles and Hut 8, and of course, Hut 6, owe very much to Commander Travis and to a lesser extent to Mr. Birch, for the energy and courage with which they sponsored its production.
The first bombe arrived in April 1940 and in August the first bombe to incorporate the vital development of the diagonal board arrived. On the 21st of December, 1940,
Mr. Birch wrote:
"The chances of reading current Enigma depend ultimately on the number of bombes available. The pundits promise that given 35 bombes they guarantee to break Enigma continuously at an average delay of 48 hours.
"At present they get the part time use of one machine. The reason that they don't get more is that there are only two bombes available and that, owing to increased complications of Air Enigma, Hut 6 requires the use of both machines. it is true that more bombes are on their way, up to a limit of 12, but the situation may well be as bad when they have all arrived, owing to the introduction of Air Enigma of further complications and owing to the further success with other Enigma colours, Air or Army.