I told Alexander and Denham that I had been indoctrinated into Operation HALT, and felt MI5 could contribute much more to GCHQ's work. I explained that tremendous advances had been made in MI5 technology since the Brundrett Committee was formed in 1949, especially in the field of new microphones. It might be possible, I suggested, to obtain HALT intelligence through technical means, rather than using agents, a method which at the present moment seemed destined for continual failure.
"I'm not sure I know myself precisely how we can help until I have had a chance to experiment," I continued, "but I am sure that with the new high-sensitivity microphones we have, it must be possible to get something out of a cipher machine. They have to be reset every morning by the cipher clerk. Suppose we could pick up the sound of the new settings being made. Wouldn't that help?"
The two cryptanalysts were supportive as I made my somewhat nervous presentation. They were clearly curious to see for themselves the first example of an unknown species in the Intelligence menagerie - an MI5 scientist.
"Any help is gratefully received in this department," said Alexander. "After all, compared to your organization, we are the new boys. We haven't even finished building yet."
He gestured to the window. In the distance a team of building workers was installing another line of Nissen huts behind the main GCHQ complex.
"Our problem is that our theories are running beyond our computer capacity," he went on.
"So many ciphers today we could crack - we know how to crack them. We just don't have sufficiently powerful computers to do the job. We'll get them soon, of course, but in the meantime, any help may give us a shortcut."
I asked Alexander what the prime target was at the moment. He looked a little uneasy at my direct question.
"Well, of course, we have many targets, they're constantly updated. JIC demands, that sort of thing."
"Yes," I persisted, "but if you had to single one out as the most important today, which would you choose?"
Alexander shifted in his seat and exchanged glances with Denham.
"I should say it was the Gyppies," said Alexander finally. "The Foreign Office have been pushing us for months to get something on the cipher. We've got little bits, but it's only now and again, and never current stuff."
It was spring 1956. Tension between Britain and Egypt was fast mounting, as Nasser began the moves which led to the Suez Crisis later that year.
"What machine do they use?"
"It's a Hagelin," replied Denham, referring to a cipher machine manufactured by the Swiss firm Crypto AG and much favored in the 1950s by Third World countries.
I arranged to borrow one of GCHQ's sample Hagelins, and took it back up to London in the boot of my car. I set the machine up with Leslie Jagger in an MI5 safe house in Regent's Park and began experiments to see if my theory was practical. This Hagelin was a keyboard machine, with tape containing the enciphered message leading out from one side. The principle of the machine was simple. Seven rotating wheels, powered by switched currents, automatically substituted mechanically produced random figures for whatever was typed into the machine. Every morning the cipher clerk operating a Hagelin inside an embassy reset the wheels before beginning transmissions. If any of our microphones could detect the sounds of these new settings being made, I felt sure that GCHQ would be able to use them to determine what is known as the "core position" of the machine, and from there be in a position to attack the cipher. Alexander and Denham explained to me that if we could get the settings of three, possibly four, wheels of the machine, they would have broken the cipher.
I installed a series of high-sensitivity microphones at various distances from the Hagelin, as well as a probe microphone in the wall behind it. Each microphone was connected in turn to an oscilloscope, so that the sounds it recorded were translated into visual readings. Leslie Jagger rigged up a film camera to record the oscilloscope screen. I opened the lid of the Hagelin and carefully reset the wheels, making a note of the old and new settings. The machine began to clatter as it enciphered a stream of dummy traffic. I sent the results down to Denham in Cheltenham for his comments.
As soon as we got the films developed, I could see that the oscilloscope readings were firm enough to provide some clue to the Hagelin machine settings. They also produced evidence of the setting of at least three wheels out of seven. I decided to make further experiments with SATYR equipment, which gave a far less sensitive sound. We did detect movements on the wheels, but it was highly corrupt. I sent the findings down to Cheltenham by courier. The next day Denham telephoned on the scrambled line.
"They're marvelous, Peter," he said. I could tell he was excited. The distortion from the scramble made him sound positively lunatic.
"The acoustic microphones are best. We can get two, maybe even three wheels out using those readings. The radio one isn't so good, but I think, given time, we might be able to make something of it."
The line fractured under a haze of static.
"When can we go into action with it?" he shouted down the line.
"As soon as you've got the ministerial clearance," I replied.
The next day GCHQ sent Ray Frawley from the planning staff up to London. Frawley was an astute, practical man, bridging the gap between the intellectual brilliance of Alexander and Denham and the administrative demands of a huge sprawling organization like GCHQ. Frawley was a radical atheist who believed that one day mankind would be coupled directly to computers. Dangerous irrationality would be banished forever. It was rather a childlike ideal for a man to hold in the grim years of the Cold War, but he and I became close colleagues even though I remained at heart an irrationalist, believing in the sudden burst of inspiration or intuition to solve a problem.
As soon as Winterborn, Frawley, and I sat down to plan the operation against the Egyptians we realized that the best way was the simplest way. I checked with the Post Office Investigations Unit and obtained a complete list of all telephone installations in the Embassy. There appeared to be one either inside or very close to the cipher complex, so we decided to install Special Facilities on the telephone and use the microphone to capture the sounds of the cipher machine. The Post Office faulted the phone system and we waited for the Egyptians to call in the Post Office. I arranged to go in myself, disguised as an engineer, with the man who would install the SF device on the telephone receiver. I wanted the chance to look over the room in case any waste cipher material was lying around.