Tony Comer, ex-GCHQ historian, has provided a short article and here is a "taster": Link: Sigint Historian: Source Protection There is more to come, see the last paragraph.
Tony back again with a short article 'Need to Know and Action-On'. Link: Sigint Historian: Need to Know and Action-On
From Bletchley Park a podcast (1h 27m) 'Security & Insecurity' and the summary states: Link: Bletchley Park / E141 - Security & Insecurity
BP has released a podcast (1hr) E157 - Security & Insecurity Part 2 with two of the three historians in E141, Dr Thomas Cheetham and Tony Comer. The precis states: Link: Bletchley Park / E157 - Security & Insecurity Part 2 (Earlier this evening I amended the thread title).
Meanwhile, elsewhere, the main protection was pigheadedness on the part of the Germans, who had convinced themselves that Enigma was unbreakable. http://rommelsriposte.com/2012/07/10/protecting-ultra-must-try-harder/ Parallels to current events abound. All the best Andreas
In Security & Insecurity Part 2 there was a short reference to the decision not to supply General Freyberg, the Crete garrison commander, with Ultra material. An issue that from memory has been well-known for many years. Perhaps it has been mentioned here, I have not looked though. Ultra knew what the German plan was though, airborne and naval - except the RN intercepted the naval element, destroying them. If fear - at the time of Crete - of capture of Ultra material, even if any such signals should be burnt after reading (referred to later in the context of 1st Army C.O. refusing to comply once) and if any POW would be interrogated successfully makes me wonder if the Australian defenders of Tobruk (for nine months in 1941) received Ultra? Not likely to be an issue with the fall of Tobruk in June 1942, as if fell swiftly. Unable to find much here about the Freyberg matter, though this comment in 2013 may help: From Post 104: Montgomery Controversy:
There would have been very little of relevance for Morshead in ULTRA, as the German or Italian army communications had not been broken. Processed information could in any case be passed on, if there was sufficient cover for it (e.g. sending out an aerial recce plane to 'spot' a convoy that ULTRA had identified). Also, Freyberg did receive ULTRA messages in Crete, according to: https://cgsc.contentdm.oclc.org/digital/api/collection/p4013coll2/id/689/download See also: The Battle of Crete 1941: The Poverty of Ultra All the best Andreas