The people involved in making the documents convincing included, beyond Montagu and Cholmondeley, a group of military officers and officials who wrote or helped write the planted letters. General Sir Archibald Nye, the Vice Chief of the Imperial General Staff, wrote the key letter — the one addressed to General Harold Alexander — that contained the substantive deception. Nye was willing to allow his actual name and position to appear on a document designed to mislead the enemy. The letter had to be convincing to a German intelligence analyst who might be familiar with how such documents were drafted, and a letter that appeared to have actually come from Nye, written in his voice and on the appropriate stationery, was more convincing than one written in a generic official style.
Lord Mountbatten contributed a letter in his role as Chief of Combined Operations. His contribution was lighter — the sardine joke about Operation Brimstone and the letter’s other purpose of establishing Martin as a known figure to Combined Operations — but his willingness to have his name used followed the same principle as Nye’s.
The intelligence and military establishment’s willingness to commit real names and real letterhead to a deception operation reflected the seriousness with which the operation was taken. If the documents were recovered and analyzed, they had to withstand scrutiny from people who knew British military culture and might try to verify the documents’ provenance. Fake names and fake letterhead would have been obvious to anyone who knew the relevant personnel. Real names, authentically written, were credible because they were real.