Large numbers of women worked at BP. The most highly skilled parts of the decryption effort were mostly carried out by men.
In "The Imitation Game",
The film gives a very different account of the work compared to accounts written by people who worked there. There were a lot more people involved in inventing new techniques and methods and in making breakthroughs. It wasn't just Alan Turing more or less all on his own. BP also worked on more than just Enigma and more than just Naval Enigma - the subject of Hut 8 which Turing led for a period.
Workers at BP
Were staff at Bletchley Park predominantly male,
In Chapter 8 p139‡ of "The Hut Six Story", Gordon Welchman describes some of the workers. One of the principle types of machine used was called the "Bombe".
No outside could be allowed inside after bombes had been delivered. The machines themselves were operated by members of the Women's Royal Naval Service, who were called "Wrens". ...
When Gayhurst became operational, bringing the total to some forty to forty-six bombes, it was still felt that the limit would be about seventy bombes, which would require suitable accommodation for some seven hundred Wrens. ...
No one could have anticipated that the number of bombe Wrens would rise to around two thousand.
Not all women at BP were operating the bombes of course, but the above may be suggestive of the types of tasks for which some, perhaps many, women were employed at BP.
The Most Highly Skilled
especially the ones involved with the most highly skilled aspects of the decryption effort?
When you write "most highly skilled aspects of the decryption process" you are probably thinking of cryptanalysts, not the more mundane (though vital) work of people why typed ciphertext into Enigma (actually British Typex) machines using settings/keys obtained by the cryptanalysts. Decryption is trivial by comparison with working out the key.
Many of the jobs, though skilled, did not require knowledge of cryptanalysis.
To understand the task of the Wren operators we must first consider the initial setup of a bombe in accordance with a menu prepared in Hut 6. ...
The in-out and out-in terminals of nine double-ended scramblers would be connected by twenty-six way cables to the diagonal board in accordance with the diagram. ... The letters under the crib positions indicate initial positions of the top, middle and bottom drums of the bombes scramblers for the start of the run. ... When a drop was sensed, ... indicators would tell a Wren which letter of the test register was involved ... Having noted all this information, which was reported to Hut 6, the Wren operator would reactivate the drive mechanism for the middle and bottom drums ...
Recruitment of young women went on even more rapidly than that of young men. We needed more of them to staff the Registration room, the Sheet-stacking room and the decoding room. .... with the whole of Bletchley Park looking for qualified women, we got a great many recruits of high calibre.
The people named by Welchman in connection with work inside Hut 6 were all male - from what I've read (though I may have missed something)
In Chapter 2 p21‡ of "Station X", Michael Smith, writes
At lunchtime, most of the codebreakers, including Barbera Abernethy, would troop out onto the lawn in front of the hous to play rounders.
However, earlier he writes that
Barbera Abernethy joined GC&CS in August 1937 at the age of sixteen, she was fluent in French, German and Flemish and when Deniston asked for a new typist, she found herself dispatched to Broadway.
So it isn't clear whether the most appropriate use was made of the skills available.
In Chapter 14 p114‡ of "Code Breakers, the inside story of Bletchley Park" chapter 14 is by Joan Murray, who wrote:
My next promotion was apparently harder to negotiate, possibly because of my sex, although there was another female mathematical cryptanalyst, working in the cottage. ...
Inevitably the duller routine clerical work was done by women.
In Chapter 6 p82‡ of "Enigma and its Achilles Heel" by Hugh Skillen, he reports Jean Alington in 3L (Hut 3 Liaison) as saying
We three women graded every German Enigma signal that came into the hut. ...
We each prepared a weekly news sheet for Mr Churchill on the areas we were covering.
So there were women working on important jobs, but the accounts
all make it seem they were a minority of those doing (arguably) the most skilled work.
- The Hut Six Story, Gordon Welchman, 2000, ISBN 0 947712 34 8
- Enigma and it's Achilles Heel, Hugh Skillen, 1992, ISBN 0 9515190 2 6 †
- Station X, Micheal Smith, 1998, ISBN 0 7522 7148 2
- Enigma, Hugh Sebag-Montefiore, 2000, ISBN 0 75381 130 8
- Code Breakers, F.H. Hinsley & Alan Stripp, 1993, ISBN 0 19 285304 X
† This is the ISBN printed on the book I own. It is now associated with a different title by the same author. I don't know if it is the same book retitled.
‡ Page numbers refer to my UK (usually paperback) copy and may not apply to other printings in other countries.