I believe that the intention was to utterly destroy the Kriegsmarine code room in Dieppe. Would that have aroused suspicion about an Enigma machine being captured? Most assuredly.
But it would have given the code breakers of Bletchley Park a leg up on German cryptography, which they eventually managed to do the hard way.
I'm inclined to buy the latest revelation based on newly released documentation as it makes more sense than telling Officers that took part in the raid that the object was to capture a port. How in hell were they going to hold it? In reality, the aim was to hold it just long enough to get a captured Enigma on board, nothing more.
Any U-boot that disappeared would also have raised questions about the loss of an Enigma machine. There was a famous convoy from Canada that was allowed to be intercepted by U-boots, resulting in several ships being torpedoed. This was after the code had been broken and the Allies did not want it to be known.
The losses were deemed acceptable. Such are the vagaries and vicissitudes of war.
We stutided the Dieppe Raid back when I was a midshipman. IIRC the Raid was meant to "raid" and cause damage. There was never an intent to take and hold anything. There was tremendous pressure from the Russians that the British and U.S. do something,
anything, to relieve pressure on the Russians. Remember at this point the Germans had yet to suffer any real reverses in Continental Euorpe or in Russia. North Aftrica was an open question as the Second Battle of El Alamein had not yet been fought. The large scale bombing offensive of the 8th Air Force was not yet in full swing. The Battle of the Atlantic was raging and not always going well for the Allies. It was not a "happy time."
I understand that siezure of an Enigma machine would be a Good Thing from the Allied perspective but I doubt it was the primary purpose of the operation.
I don't know of any convoys that suffered the fate of Coventry (where no special defense was raised even though the RAF knew of the raid hours ahead of time from an Enigma intercept). A couple were "broken up" and ordered to proceed indepenantly due to intense U-Boat operations. We really didn't need Enigma to tell us where the U-Boats were; they did that for us by their constant communications with their HQ in France and some very good HF/DF work. Convoys were routinely routed around known U-Boat concentrations, if that was possible (and sometimes it wasn't).
The difficulty was that an HF/DF fix was a pretty big circle (several nautical miles) and ASDIC/SONAR ranges were measured in thousands, and sometimes hundreds, of yards. There was a dreadful shortage of escorts. If you got a contact then you had to run over the position, drop the depth charges, and see what happened. Often the acoustic disturance of the water from multiple explosions was enough to give the U-Boat a place to hide or an area of "disturbed water" to escape through.
Certainly a lost U-Boat might mean a lost Enigma machine. But if the KM were to alter Enigma after every U-Boat stopped making reports they'd never have any working machines. So they had to proceed on the theory that capture of a sub was a virtual impossibility. IIRC there were only two prior to War's end. Both were kept Top Secret (much to the chargin of RADM Gallery who wanted a PR coup for the ASW forces).
It's possible that the documentary is right; it's also possible that the whole theory is "revisionist history" by academics who've never walked a deck or flown a MAD trap.
SQQ