The first opportunity to have the Legation premises thoroughly inspected for security purposes by British experts, in accordance with the instructions contained in your Chancery P.I.46/11/7/5 of 29th November 1946, occurred last month after the start of the Moscow Conference. The United Kingdom Government was successful in obtaining visas for several technically trained men as members of their Delegation. On Monday 17th March the Administrative Officer of the British Embassy brought Messrs. Dunnett and Forty for a preliminary investigation. Starting their search in the Minister's office on the first floor, which I have been occupying, they made their first discovery within ten minutes: a microphone embedded in concrete exactly at floor level behind the skirting board on one of the two outer walls. Their first clue was provided by a shallow groove cut on the underside of the skirting board, and visible only to an expert eye.
They then temporarily suspended their activities at this Legation, as they had received instructions to inspect all British and Commonwealth premises in Moscow, and determine which were wired, before taking any steps for the disconnection on dismantling of apparatus or its removal from any establishment. The Legation was not the first building which they had found to be wired and they anticipated further discoveries. Their own position was not an easy one, as by this time the nature of their activities and the purpose of their visit to Moscow must already have been suspected by the Soviet authorities, and there was at least a possibility that their visas might be revoked on some pretext or other. It was therefore not until Wednesday 26th March that a full inspection was undertaken here.
Meanwhile various incidents indicated that some Soviet authority, presumably the MVD, was worried as to what had taken place at the Legation on 17th March. On Friday 21St March an electrician was sent by 'Burobin' , ostensibly 'to inspect all the electrical installations in the building'. Such an inspection had never, to our knowledge, taken place before, so Alexander  sent him away and rang 'Burobin' to say that we were too busy to be troubled with any workmen in the building for the duration of the Conference. On Monday morning 24th March the housemaid, while cleaning the Minister's office, managed 'accidentally' to pull the wiring of the telephone extension from the wall, a feat requiring a certain amount of strength and determination, and I was just in time to prevent a call being put through to 'Burobin' to send someone immediately to repair it. The most cursory glance around the room would have revealed to a trained eye that the skirting board had been removed from one wall and replaced. It was reasonably certain now that the Soviet authorities concerned were very anxious to ascertain the nature and extent of our discoveries, if any. On Tuesday evening 25th March Mr. Bridge, Administrative Officer of the British Embassy, called to see me to announce that operations for the removal of all apparatus from the building would commence the following morning. In the small hours of the night the direct telephone in the Minister's office rang continuously for an hour from approximately 4 a.m. to 5 a.m.
Wednesday 26th March. This telephone, which had been installed at the same time as the switchboard downstairs, was intended solely for direct outward calls. The number had not been notified to anyone outside the Legation and yet when the room was empty or quiet the phone would often ring gently. If one answered one was greeted either by silence or an abrupt 'Who is that?' but received no indication of the identity of the caller. Also every night between midnight and one a.m. the phone would tinkle once or twice. Our suspicions had been aroused, and I was inclined to agree with Rowland's  suggestion that, if there were a microphone in the room, the ringing of the telephone, at times when the room or the house was silent, might provide a means of testing whether it was working properly.
On Wednesday 26th March Dunnett and Forty set to work about noon and worked right through until 9 p.m. without leaving the building, as it was felt advisable to reduce the number of comings and goings as much as possible. They ate their meals in the room in which they were working. From the outset the diplomatic staff, Alexander and Rowland, were informed of the nature of the British experts' activity and of developments as they occurred. When it became necessary for them to start work in the offices downstairs I had to inform the Australian clerical staff, the Crawfords and Dalton , that the building was being 'vetted', but they were warned not to mention the fact to anyone, and at no stage, either then or subsequently, were they given any reason to believe that anything had been discovered. Our two translators, for their own protection, were told nothing and have asked no questions.
Whatever they may have suspected they know nothing. The domestic staff, and in particular the housemaid, must have had some idea of what was taking place by the end of the first day, but there was little likelihood of their mentioning the matter, except to the MVD to whom it would be no surprise and who would certainly give it no publicity.
Within ten minutes of resuming their search the British experts, by a stroke of luck, located the central distribution point for the whole house beside the fireplace in the small reception room next to the Minister's office. (I would refer you to the plan of the Legation for-warded under cover of our Statement of Establishment, Staff and Organisation of 20th August 1946. We relinquished our only copy to the British technicians for use in the preparation of their report, and they will return photostatic copies. A plan of the house will no doubt in any event accompany the technical report which is being forwarded to you from London.) The mesh of leads was embedded in concrete under the floor boards, and the concrete had to be chopped away to a depth of several inches before anything was revealed. From the number of leads it was clear that there must be 14 or 15 microphones in the building.
(Subsequent evidence showed that there were only 14). The two which had already been discovered, in the office and the reception room, like almost all the others which were discovered subsequently, were set in the wall at the level of the floor boards, with the wiring below floor level. All were embedded in concrete which, I am informed, has the effect of amplifying sound, where wood deadens it.
At this stage an oscillator was connected with the leads and 'buzzed', but only two microphones 'sang', one in my bedroom (formerly occupied by Mr. Maloney ) and one in the small office off the Chancery, at present occupied by Rowland. This latter caused a slight stir in the office. The two microphones which 'sang' were those which were furthest from the main distributing point, at the end of the upstairs and downstairs systems respectively. It appeared that the Soviet authority concerned, when convinced that a thorough search was pending, had put high voltage current through the wires and 'killed' all but two microphones, with the object of making detection, by such methods as the oscillator, more difficult. Most of them, when found, bore evidence of having been 'killed' in this fashion. This had probably been done during the night of Tuesday 25th - Wednesday 26th March, only a few hours before our investigations were resumed. The continuous ringing of the 'mystery' telephone in the Minister's office in silent house in the small hours was no doubt to test whether all the microphones had been silenced.
The search was completed by 7 p.m. or thereabouts on Thursday 27th March. Altogether in two days 14 microphones were discovered. By following the leads back the investigators found the main 'feed' entering the building through the entrance hall near the militiaman's shelter. Embedded in concrete under the tiles of the floor, it crossed the entrance hall and climbed an inside wall to the central distributing point for the whole house, both upstairs and downstairs, under the floor boards beside the fireplace in the small reception room. From there one lead fed the microphone in the Minister's office. The others crossed the room into the large reception room and there separated into two main systems, upstairs and downstairs. The upstairs wires led through the large reception room to the dining room, and thence to the large room at the back of the dining room, and back through the second bedroom, breakfast room and first bedroom. The downstairs system had its distributing point beside the main door of the Chancery and fed five microphones, one each in Alexander's and Rowland's rooms and the entrance hall, and two in the Chancery. Upstairs there were nine microphones, one each in the office, the small reception, dining and breakfast rooms, two bedrooms and room off dining room, and two in the large reception room.
The British experts were impressed with the installation. They said it was the most carefully installed system they had seen, elaborately concealed so that only by pulling up floor and skirting boards could any clue be found, and not necessarily even then, as all the vital parts were embedded in concrete. They estimated that it would take two men, working full time, over two months to install. In Russia it would probably have taken longer than that. It seems that it could only have been installed when the building was empty, although the possibility cannot be ruled out of its having been overhauled and repaired between March and June 1945, when structural repairs were effected in all the front rooms on the first floor, following a fire which broke out on Red Army Day in the small reception room. (See Despatch MU12 of 12th March 1945). It may or may not be a coincidence that the seat of the fire and centre of subsequent repair operations was within a few feet of the nerve centre of the wiring system. I understand that the floors in the back rooms on the first floor were also repaired at the same time. The period of the repairs coincided in point of time with the Minister's visit to Australia (April and May 1945).
The alterations undertaken by 'Burobin' between October and December 1946 were limited to painting of walls and ceilings. No structural repairs were undertaken, except in the main bathroom and the second-floor bedroom, both of which were free from wiring or microphones. The workmen were permitted to occupy only one room at a time and any attempt to remove floorboards would have been instantly noticed. Neither in 1945 nor in 1946 was any work performed in the offices downstairs.
I have typed four copies of this report, of which I enclose three copies. The fourth copy is being retained in this office under lock and key.
I forward as an attachment to this report the two microphones which were found in the Minister's office and Alexander's office.
All other microphones, together with samples of the leads, wiring, concrete, etc., were sent to London for study and use in the preparation of a technical report which should by now be completed, and copy of which, together with specimens, is to be forwarded to you by safe hand from London. My report is intended to supplement the technical report.
In addition to Alexander, Rowland and myself, the following members of the British Embassy staff are the only people in Moscow who are aware of any of the details set out above: the Ambassador, Sir Maurice Peterson, the Minister, Frank Roberts, two First Secretaries, R. Allen and D. Macfie, the Administrative Officer, H. Bridge and the Security Officer Gilmore. Although there were over 80 foreign journalists in Moscow during the Conference full secrecy has been maintained.