Late to the party as usual . . . but as found in the documents available from the George C Marshall Library-Foundation (https://www.marshallfoundation.org/library/results/?fwp_format=2), Winston Churchill, indeed, wrote on the subject of code names. In a memorandum of 8 August 1943 he wrote to General H. L. Ismay, his chief military assistant, evidently in response to a listing of code names:
1. I have crossed out on the attached paper (marked A) a large number of unsuitable names. Operations in which large numbers of men may lose their lives ought not to be described by code-words which imply a boastful and over-confident sentiment such as “TRIUMPHANT”, or conversely which are calculated to invest the plan with an air of despondence, such as “WOEBETIDE”, “MASSACRE”, “JUMBLE”, “TROUBLE”, “FIDGET”, “FLIMSEY”, “PATHETIC”, and “JAUNDICE”. They ought not be names of a frivolous character, such as “BUNNYHUG”, “BILLLINGSGATE”, “APERITIF”, and “BALLYHOO”. They should not be ordinary words often used in other connections, such as “FLOOD”, “SMOOTH”, “SUDDEN”, “SUPREME”, “FULLFORCE”, and “FULLSPEED”. Names of living people or Ministers or Commanders should be avoided, e.g. “BRACKEN”.
2. After all, the world is wide, and intelligent thought will readily supply an unlimited number of well-sounding names which do not suggest the character pf the operation or disparage it in any way and do not enable some widow or mother to say her son was killed in an operation called “BUNNYHUG” or “BALLYHOO”.
3. Proper names are good in this field. The heroes of antiquity, figures from Greek and Roman mythology, the constellations and stars, famous racehorses, names of British and American war heroes could be used, provided they fall within the rules above. There are no doubt many other themes that could be suggested.
4. Care should be taken in all this process. An efficient and a successful administration manifests itself equally in small as in great matters.
On 23 September 1943, Leslie Rowan, Churchill”s private secretary. sent the above to Lt. Col. Frank McCarthy of General George Marshall”s staff in Washington under this cover:
Herewith are the Prime Minister’s minute about code names and the list of code names which he promised to send to General Marshall. As I told you, I could not let you have this at Washington because we had not the list available.
Thank you very much for your kindness at Washington, and especially for the dinner party. I hope that I shall be able to return your hospitality.
General Marshall responded to the Prime Minister on 1 October 1943:
Dear Mr. Prime Minister:
I received your minute to General Ismay on code names and took the matter up immediately with our Joint Security Control.
All are in agreement with your views. In the future, the names recommended for projected operations will be selected in accordance with the principles which you outlined.
G. C. Marshall
The list of code names, with strikethroughs can be found here
And this, from 1 September 1943, might be interesting: