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Setting The Scene

Imaginary Conversation 1

Imaginary Conversation 2

Imaginary Conversation 3

Imaginary Conversation 4

Back To Reality

Setting The Scene

It is 1939.  There is a war on.  This text will self destruct as soon as you've read it.  You are sworn to secrecy.  Walls have ears.  I know this, as I've just found one in my ice-cream.  Individuals can't be identified until 30 years have passed, so have been given code names and different service ranks.  All of this is completely factual and hush hush.  Some of it is almost true.  I can't say which parts.  You never know who is listening.  Shhhh...

Imaginary Conversation 1

The participants

Man = A man from the street. Can't say which street.

Dinosaur = Lord High Admiral, Chief General of All UK Armed Forces.  Can't say which ones.

The conversation

Man:  (Knock, knock.)

Dinosaur:  Come in.

Man:  Hello, is this the office of the Lord High Admiral?

Dinosaur:  (Pause)  Look here old chap.  There is a war on, you know.  Walls have ears and all that.  If it was that office, I couldn't really admit it, could I?

Man:  But it says so on the door.

Dinosaur:  Does it?  Damn! I'll kill that Security Officer!  Well just for the sake of conversation, if this was that certain office, and I'm not saying that it is, what do you want?

Man:  It's a bit difficult knowing how to put this.  I'm in a delicate situation.  Let us say that I have a friend.  Yes, that's who I'm talking about.  A friend.  Not me.  You know that all the UK Radio Amateurs have had their radios confiscated in case any of them were spies and wanted to transmit secrets back to Germany? 

Dinosaur:  Sorry old boy, you've lost me there.  I thought a radio ammeter was some sort of dial thing which measured electric current?  Are you saying that your friend measures electric current?

Man:  No, no. Radio Amateur. I transmit...  I mean my friend transmits on his radio to other people and experiments with aerials and designs radio circuits using high powered pentode valves.

Dinosaur:  Hhhmm.  By jove, I think we are getting there.  Do you mean that your friend is a radio ham?  One of those strange people with long hair and suede shoes, who spends hours tinkering about with wires and soldering irons?  Is that the sort of chappie your friend is?

Man: (Looks down at his suede shoes, then looks up)  Yes, that's it. A radio ham. Well, as I was saying.  You remember that they all got their radios taken away by the police?

Dinosaur:  No.  Can't think why the police would do that.  I wouldn't have thought that those radio hams could have transmitted on their wireless as far as from here to Trafalgar Square.  I can't really see that forming much of a threat to the nation.  I'm sure you agree.  Would you like me to give them back their wirelesses?  I could probably arrange that for you.

Man:  No.  Well, yes, it would be nice, but that's not why I came here.  My err.. friend hid some of his radios before the police arrived.  He still has some of his gear.  In fact, it's worse than that, he knows several other hams who still have their radios.  I'm in a bit of a delicate situation with this...

Dinosaur:  Superb!  This is just the sort of good citizen attitude that we in Whitehall are trying to promote.  So you are here to inform on your friends for breaking the law.  Excellent!  I'll have them shot.  That Hitler fellow has made an enormous amount of progress in getting his people to inform on each other.  I'm glad that we in the UK are finally doing the same.

Man:  (Imagines smoking a last cigarette, before being shot)  You misunderstand. My friends have been receiving Morse Code signals.  They were in five character groups, which means they are in secret code.  

Dinosaur:  What's a five character group?  Are your strange ham friends also folk singers?  Or is it even worse than that?  Are they Morris Dancers?  I'll definitely have them shot!

Man:  If you encrypt a message into secret code, but leave the spaces between words unchanged, it's not very good as it can be seen how many letters there are in each word.  So you use five characters followed by a space, then another five characters and so on.  These secret code radio signals are being transmitted from Germany.

Dinosaur:  Good Lord!  That's asking me to believe a little too much!  My incredulity is stretched to its limit.  Where on earth could they buy a telescope of such magnification that they could tell that the signals were coming from Germany?  It must be 600 or 700 miles away.

Man:  To be more exact, 543.2 miles away on a bearing of 75 degrees from true north.  Berlin.  Probably Leipzig Strasse.  I think it's number 27 but others think it could be number 28, on the second floor.  Third room from the front.  The one with green curtains.

Dinosaur:  (Jaw drops)  Well, I'm flabbergasted.  My flabber is completely well and truly gasted. How could anybody tell where a wireless signal is coming from?

Man:  They use directional aerials to get bearings, then do simple trigonometry for a flat earth approximation.  For higher accuracy, they use spherical geometry.  It's not always accurate, but it's usually quite good.

Dinosaur:  (Looks stunned)  I have absolutely no idea what you are talking about, but I like the cut of your jib.  What else do I need to know?  If it's important, you'd better write it down for me.  All I heard from you was some gobbledygook strange sounds which could be words.

Man:  (Man writes)  I've written down six frequencies which are quite busy with coded signals.  if you give them to somebody, they can confirm what I've said and try to decode the messages.

Dinosaur:  Of course.  Splendid idea.  I'll give the piece of paper to somebody.  But there are so many people in this building.  Who?  Doris the tea lady is very understanding.

Man:  I suggest somebody who knows about radio.  Perhaps a senior wireless operator in one of the forces?

Dinosaur:  Yes, excellent!  The RAF are no good.  They just haven't got their feet on the ground.  The Army just drink tea all day. The Navy!  They're the best.  Lots of wirelesses on all of their ships.  Come back here in a week and I'll have a medal waiting for you.

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Imaginary Conversation 2

Man: (Knock, knock)

Dinosaur:  Come in.

Man:  Good morning, sir.  Remember me?  You told me to come back in a week.

Dinosaur:  I remember you very well.  You've no idea how much trouble you've caused and how much valuable time you've wasted.  I've made myself a laughing stock.  All because I believed you, even though I couldn't understand a word of what you said.

Man:  What do you mean?

Dinosaur:  I gave your piece of paper to a colleague in the Royal Navy.  He gave it to some wireless expert.  Back came the reply.  No secret coded signals on any of the wavebands.  In fact, nothing there at all.  Total silence!  No wireless signals of any flavour.  Well I remembered that you had a kind face and meant well, and that you were of a very high moral character by informing me about your ham friend's illegal activities.  I then gave your piece of paper to the Army.  Same result!  It's conclusive.  If the Army actually agree with the Royal Navy, it's a rare thing, so it must be true.  There are no wireless signals.  What have you got to say for yourself?

Man:  The signals have been constant all week.  They are always there. My friend has heard many more.  All in Morse Code.  All of them encrypted.  All of them from Germany.  I could let you hear the signals, but I wouldn't want my friend to go to jail for keeping some of his radios when the police came to confiscate them.

Dinosaur:  Aha!  You've said too much.  You have now unwittingly provided me with the method of making you look as silly as I have for the past week.  It's too late for you to get out of it.

Man:  But...

Dinosaur:  (Picks up telephone)  I want two fast cars outside this building in ten minutes.  They will have three passengers, each of them with an expert knowledge of wireless and Morse Code.  Make it happen now!

Man:  I'm sorry to cause so much trouble.  I just thought that somebody should know about the secret radio signals.

Dinosaur:  But there aren't any signals, secret or not.  As we'll prove shortly when you guide us to your friend's house.

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Imaginary Conversation 3

Man:  This is the house here.  The one on the right.

Dinosaur:  The one with the green door?

Man:  No, the one next to that one.  The one with the two radio masts and thirty-six aerials.

Dinosaur:  Will your friend be at home?

Man:  Actually, I wasn't completely truthful with you...

Dinosaur:  We know that!  It is the reason we are here.  To prove you a liar.

Man:  What I meant was, it's me.  I'm the one who listens to the secret signals.

Dinosaur:  I'm astounded!  You certainly had me fooled.  Yet another lie.  Let's get on with it.  Come on, you lot.  Follow this liar.  And keep an eye on him.  Make sure he doesn't do a runner.

Man: (Enters house and leads his escorts upstairs)  This is my shack.

Dinosaur:  Eh? Colonel, what did he say?

Colonel:  Didn't understand him, sir.  Sounded like swearing to me.

Rear Admiral:  He said it's his shack.  He must be a Navy man. Is that right?  Were you a sparks in the Navy at one time?

Man:  No, sir.  I've been a grocer all of my life.  I'll just turn on my rigs and let them warm up.

Colonel:  Isn't that a biscuit tin you've just turned on?

Man:  Sort of, sir.  I couldn't find any aluminium for chassis bashing, so I used biscuit tins reinforced with plywood to make my receivers.  They're not very pretty, but they seem to work.  The small one is a simple double quenched regenerative model.  It's quite terrible on frequency stability but not bad on sensitivity.  The big one took me quite a while to get working.  It's a superheterodyne with a front end RF amp, capacitor tuned variable local oscillator and mixer in the same bottle,  an intermediate frequency stage, amplitude detector and of course audio amp.  I'm never too happy about the frequency calibration, so I check it against harmonics of a one Megacycle crystal calibrator and a one hundred kilocycle crystal calibrator.  Of course, I still have to interpolate to some degree.

Dinosaur:  What did he say, Colonel?

Colonel:  He said that he made it himself, sir.

Dinosaur:  Do you actually understand his lingo?  Do you catch his drift?

Colonel:  Err, yes, sir.  I think so.

Man:  (Valves warm up.  Morse Code signals heard from the loudspeaker)   I'll just switch from my long wire to my RDF loop.  Oh yes, that CW signal is at 63 degrees, so its further north than Berlin.  I would have to get my friends to give me cross bearings before I could be sure of the fix, but I suspect it is Hamburg.

Dinosaur:  What did he say, Admiral?

Rear Admiral:  He believes that he's listening to Morse Code from Hamburg, sir.

Dinosaur:  And is it Morse Code?  Sounds like it to me.  What does it say?

Rear Admiral:  I'm afraid that I'm a little rusty with CW, sir.  I'm more used to copying Morse from an Aldis lamp.  It'll come back to me in a while.  I'm pretty sure that it sounds a little French, rather than German, but I couldn't be certain at present.

Dinosaur:  Well, Colonel, is it secret code from Germany or a blasted frog trying to confuse us?

Colonel:  I would need a little time, sir.  Like the Admiral, I'm a bit rusty.  I think that I would agree with him that some of it has a slight French accent.

Dinosaur:  What do you think, Sergeant?  Is it French or German?

Sergeant:  Haven't got a clue, sir.  Where I come from in the east end of London, we don't tend to speak much French or German.  But I can tell you that the last bit we heard was HYR4S PA2T5 ZDCWQ 9L8UM.

Dinosaur:  Are you telling me that the entire British Armed Forces can't receive any of this stuff, yet our grocer friend here, with his biscuit tins, can not only receive it, he can tell which town it's coming from?

Sergeant:  Not sure, sir, but it certainly looks that way to me.

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Imaginary Conversation 4

Dinosaur:  Welcome, welcome.  Nice to see you.  Glad you could accept my invitation.  Would you like a spot of tea?

Man:  Thanks very much, sir.  Very kind of you.

Dinosaur:  Here we are.  Help yourself to the sugar lumps.  What do you know about Bletchley Park?

Man:  Never heard of it, sir.  What is it?

Dinosaur:  I'm so glad that it means nothing to you.  It proves that the secrecy is completely intact.

Man:  If I may hazard a guess, sir?  Would you be setting up a secret military base, with extremely clever and talented civilians?  Will you be placing covert adverts in the newspapers asking for mathematicians, scientists, linguists and people who can do The Times crossword in ten minutes and are Grand Masters at chess?  Would the function of this military base be to decrypt my secret Morse Code signals from Germany?

Dinosaur:  Well, of course we are!  Any fool could have guessed that.  It's the obvious part, but there is a lot more to it. We're after a clever chap called Alan Turing.  He's a bit queer, but all these clever people are eccentrics.  We expect him to find the problem of decrypting those secret code messages difficult and presume that he will have to invent the world's first computer.  I suppose he will probably call it something grand, such as Colossus.

We already have a team of GPO engineers from Dollis Hill Research Station standing by with relays, valves and all sorts of who knows what odd and ends to make this computer.  Unfortunately, they can't be sure which parts they need, as nobody has invented a computer before or knows what one is or does.

The problem we have at present, is finding the qualified manpower and wirelesses which are capable of receiving the secret wireless signals.  We thought that perhaps you may help us out?  Perhaps you and your friends?

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Back To Reality

A tiny essence of the above is correct.  Radio Amateurs were the people who copied down the encrypted HF radio messages which were the source of the information sent on to Bletchley Park for eventual decryption.

During the wars years and for many years afterwards, the Radio Amateurs never knew what signals they were copying or where their transcripts were sent to.  This was because of the Official Secrets Act and a standard method of maintaining good security by compartmentalising different departments and not letting each one know what the other one did. 

The original signals were intercepted from the Abwehr, Gestapo and SS in Germany.  The Abwehr was the military intelligence section of the German Army.  They assured top Generals that their radio signals couldn't reach the UK.  They were wrong.

The Abwehr were also able to prove mathematically to Hitler that the Enigma machines, which were used to encrypt and decrypt messages, were so complicated that it was totally impossible for anybody to break the codes.  In addition, passwords were changed frequently.  They were wrong.

It is now common knowledge that Bletchley Park became able to read much of the German secret coded radio messages which were transmitted from Germany and from U-Boats.

The Voluntary Interceptors (VIs) copied down the coded messages.  The VIs were part of the Radio Security Service.  Many of them were looked on with suspicion by neighbours.  Their ages indicated that they should probably be in the military, but they were never seen in a uniform.  They didn't seem to work in munitions factories or be in the Home Guard.  They wouldn't say what they did.

In some cases, neighbours were convinced that VIs were spies.  They would be spotted leaving home in the morning and going across fields into the woods.  Some slept all day and crept out in darkness to go into the woods, not returning until the following day.  They can't have been poachers, as they never carried anything large enough to contain guns, deer, rabbits or pheasants.

There are stories about VIs being arrested by the police on suspicion of being spies.  On being asked why they weren't in the army or a munitions factory, they wouldn't say.  All they would say, was that the constables should get their Inspector to ring a certain telephone number and say that they had arrested a man and to give the name of the arrested man.  Ten minutes after this was done, the Inspector told the constables that they were to release the prisoner.  He had never been arrested and didn't even exist.  If he was ever seen again, he must be ignored, as he didn't exist.

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Coordinated RDF

Once the VIs had been organised and controlled by military intelligence, official receiving stations were established all over the country.  Each had a radio receiver, a normal aerial and a radio direction finding (RDF) aerial.  These radio intercept stations were all connected to a central location by GPO private circuits.  Military intelligence was interested in two aspects of intercepted enemy radio signals, the content and the transmitter location.

Signal sources could be found quickly and efficiently as follows.  The Controller decided which radio transmission was of interest at the time.  He listened to it on his own radio receiver.  He spoke to all intercept stations at the same time using the GPO omnibus private circuit.  He announced the radio signal's frequency in kiloHertz (in those days it was kilocycles per second) and then connected the headphone socket of his radio receiver to the GPO private circuit.  Each intercept station tuned to the given frequency. They used split headphones.  The right ear heard the local radio.  The left ear heard the GPO private circuit.  If several signals could be heard at the same time in the right ear, the VIs knew which was of interest as they could hear it in the left ear.  Each intercept operator used his RDF aerial to get a bearing on the target signal.  In some cases, if all went well, this could be done in a few seconds.

All bearings were passed back to the Controller and plotted on a map.  Any single bearing could have been wrong or inaccurate, but with so many bearings on the same signal, the location of the transmitter was obvious.

For more information on RDF, see here.

The book "The Secret Listeners" is about the work of the Voluntary Interceptors.  Don't tell anybody, but there is a "Secret Listeners" chat net on 3.720 MHz at 09:00 hrs on Mondays and Fridays.  Some really ancient callsigns can be heard on this net.

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Bletchley Park Colossus is being rebuilt

The Radio Security Service

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Page updated on 09 January 2017

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