Analysis of information sources in references of the Wikipedia article "Battle of Crete" in English language version.
The first convincing demonstration of this potential in operational conditions came in May 1941, when the entire plan for the German airborne capture of Crete was decrypted two weeks before the invasion took place.
It appears that General Freyberg was introduced to Ultra only shortly before the battle of Crete began and therefore had no time to become familiar with its proper interpretation. This situation was exacerbated by the fact that 'he was forbidden to show it (the information derived from Ultra) to anyone or to discuss it with his intelligence staff.' [...] Moreover, tight security regulations prohibiting him from taking action on the basis of uncorroborated Ultra evidence limited its value.
The first convincing demonstration of this potential in operational conditions came in May 1941, when the entire plan for the German airborne capture of Crete was decrypted two weeks before the invasion took place.
It appears that General Freyberg was introduced to Ultra only shortly before the battle of Crete began and therefore had no time to become familiar with its proper interpretation. This situation was exacerbated by the fact that 'he was forbidden to show it (the information derived from Ultra) to anyone or to discuss it with his intelligence staff.' [...] Moreover, tight security regulations prohibiting him from taking action on the basis of uncorroborated Ultra evidence limited its value.