How Vinyl Helped Beat Hitler

This blog is the result of hearing a radio report about the redevelopment of Trent Park, a former stately home in North London, into a number of luxury flats. Of particular interest to me was the its use as a Prisoner-of War camp in the Second World War to hold captured German Generals.

Trent Park

Trent Park: Holiday (Prison) Camp for Hitlers Henchmen

These high-ranking officers, who numbered 59 by the wars end, where not simply prisoners to the Allies, who’s capture ruled them out of the fight, but valuable sources of intelligence due to the secrets they had been privy to when serving officers.

The issue was how to get them to talk and reveal all they knew.

And this is where MI19, the branch of military intelligence entrusted to do this, becomes of interest to the professional audio engineer because of the techniques they employed in doing so.

In order to extract as much valuable and, crucially, truthful information out of the Generals as possible, the British set Trent Park up, along with two other locations for high-ranking PoWs, almost as a high-quality hotel: with a day-lounge, individual bedrooms and pleasant grounds to stroll in, so as to relax their prisoners as much as possible and get them to talk freely amongst themselves. And this is how the intelligence was gathered, because each room and the grounds were bugged with microphones, placed in light fittings and even trees in the gardens, all with the aim of listening-in to their conversations.


German Generals Trent Park

"All together now. Say "Heil""

The output of the microphones were fed, via cables, to RCA produced monitoring equipment in adjacent buildings and operated by German speaking listeners, many of whom had escaped from Germany before the war. Their task was to listen across three bugged locations to the conversations the microphones were picking-up and, when something of significance was heard, record it on a direct-cut disc for future transcription and analysis.


Trent Park Listener 2

"Can I have a few words for level please?"

For the audio engineer of particular interest in this operation was the equipment the system used:

• Each location took four to six months to wire up.

• The equipment was manufactured in the USA by RCA (Radio Corporation of America).

• The microphones used were the company’s 88A model.

• The operators would monitor the three bugged rooms allocated to them on headphones and switch between them using a post-office A-gauge patch panel.

• The conversations were recorded on 12” double-sided acetate direct-cut discs, the resultant recording was then transcribed to paper.

Of note is the incredible feat of hiding the microphones and still making what they picked up audible. This is near 80 year old technology we are talking about, there were no electrets or tie-clip sized capsules. Secreting a moving-coil device with significant sized outside dimensions of 114mm long by 54mm in diameter is no easy task. And just how they environmentally protected them when used out in the grounds is anybody’s guess!


RCA 88A 2

The RCA 88A: Not what you'd call the easiest thing to hide...

The conversations they picked up however were far from insignificant. Valuable knowledge on the V1 flying bomb and V2 missile was gained through one particular General who was known to be a bit of a chatter-box. On a darker note, information about the systematic mass-murder of the civilian population in the German occupied territories was also recorded and used as part of the evidence in post-war war-crimes trials.

The actual transcripts of the conversations remained classified until 1999 and even after hostilities ended that fact that the British had used such intelligence gathering techniques and technology remained a secret so as to continue its use in the cold war.

It is hoped that a museum will be set up in part of the refurbished building to illustrate what went on during its use as a PoW camp. If this happens it will not only be a testament to those with an interest in the Second World War but also to audio engineers and the varied applications the equipment we work with gets used for.


The title of this blog alludes to vinyl records being used as the medium for the direct to disc recordings, although as mentioned, they were in actual fact acetate discs. Either way the disc recording technology of the time left a lot to be desired, probably making replay a hard listen.

A better solution would have been to use a tape recorder, although it was very early in its development, the quality obtained was very much higher. The issue was obtaining them, since the best product available was the Magnetophon, produced by the German company AEG.

Oh the irony if that had happened..

Iain Betson