THE CLOSING OF THE UK
CENTRAL TELEGRAPH OFFICE (CTO)

An extract from the
Post Office Electric Engineers Journal
Volume 54, Part 3 - October 1961

The Closing of the C.T.O.

The Central Telegraph Office, once the largest telegraph office in the world, will be closed in 1962. The history of the building itself, which was opened in 1874, and the many technical and operational changes that have taken place within its walls are briefly reviewed.

After nearly 90 years on its present site in St. Martin's-le-Grand in the City of London, the Central Telegraph Office (C.T.O.) is soon to be closed and the building demolished. Because of inevitable changes in techniques the building has now outlived its original purpose as a central office. Its closing will mark the end of an epoch during which the work of the C.T.O. not only contributed to the science of communications but also, because of the knowledge gained by the application of the principles of electricity to many and varied systems of telegraphy, exerted an influence in the wider sphere of electrical engineering.

The Institution of Electrical Engineers was founded in 1871 as the "Society of Telegraph Engineers," many of whose members had a technical interest in the C.T.O. This interest continued through the years spanning the period of the single-needle, the double-plate sounder and Morse key, the many variants of machine telegraphy and finally the teleprinter and the voice-frequency (v.f.) channel.

This brief review recalls some of the many changes that have occurred during the life of a building that has dominated the telegraph scene for so many years.

Due to a variety of causes, including the effects of several severe winter storms on the overhead line networks, there was, in the late 1860s, considerable public dissatisfaction with the service being provided by the existing telegraph companies. The Government was pressed to place the telegraph service under the control of the Post Office and, in 1869, after exhaustive negotiations, Mr. Gladstone announced agreement with the telegraph companies for their purchase. The sum paid was £54 million and the Postal Telegraph Department took over the head office of the Electric Telegraph Company in Little Bell Alley off Moorgate. The name of the alley was changed to Telegraph Street and the letters TS became the call sign of the Central Office. The rapid growth of business soon rendered the Telegraph Street premises inadequate and the Post Office decided to occupy part of a building then in course of construction in St. Martin's-le-Grand.

The building was completed in 1874; an additional storey was added in 1884 and the building was enlarged in 1901 and 1902. In 1930 a fifth storey was added, and further changes included the removal of the pneumatic-tube system from the central hail to another part of the building and the conversion of the hall to a lecture theatre, which was opened in 1935 as the King George V Hall. It seated 325 and was equipped for film projection and was also used for lectures and exhibitions. Fig. 1 shows the C.T.O. as it was in the early 1930s.

FIG. 1 - THE C.T.O. IN THE 1930's

The transfer from Telegraph Street to St. Martins-le-Grand figures in the Postmaster-General's report to the Treasury in 1874, in the following terms:
"At the end of the year the London Central Telegraph Office was removed to the new office in St. Martin's-le-Grand. So well had everything been arranged and so zealously and effectively were the arrangements carried out that no interruptions of any kind occurred; indeed, the provincial clerks were not aware of the change. The great telegraph business which had been conducted in Telegraph Street was on that night as the clock struck 10 taken up without the slightest hesitation or confusion in the new Post Office Building."

Telegraph business flourished in the new central office; traffic assumed definite patterns - metropolitan, provincial, overseas, and press. By far the greatest increase was in press telegrams, which in the year 1290 totalled 5,003,409. The press tariff, however, was so low (2d. per 100 words) that, although it operated only after 6.00p.m., it virtually represented a form of subsidy to the press by the Post Office.

Cable companies, stock exchanges and branch telegraph offices originated most of the traffic, much of which was received and re-transmitted through some 40 miles of pneumatic tubes, extending to the Great Tower Street branch office in the east and the House of Commons in the west.

During the period 1890 to 1900 development continued; overhead lines were being put underground and the "wires" (18 B.W.G. copper insulated with gutta-percha to an overall diameter equivalent to 7.5 B.W.G.) were routed into the C.T.O. in 3in. cast-iron pipes, 80 wires per pipe. It is also noteworthy that at this time the main source of telegraph power in the C.T.O. was primary cells housed on 21 miles of teak shelving in the basement. Approximately 12,150 quart-size bichromate cells were used for heavily-worked and long-distance circuits together with 10,700 large Daniell cells for duplex circuits and for circuits up to 150 miles in length.

About 900 Leclanché cells were also in use for lightly-worked circuits, while secondary cells were introduced during this period for the Hughes printing instruments used on Continental lines.

Precise timing became increasingly important with the growth of inland and overseas traffic and the C.T.O. became the national and international time-distribution centre, transmitting Greenwich Mean Time which was checked daily by a signal from the Royal Observatory.

In 1889 the Post Office purchased the interests of the Submarine Telegraph Company and, using mainly the Hughes and Baudot systems, operated from the Cable Room 10 cables to the capitals and principal cities of Europe.

At the beginning of this century a multiplicity of systems were in operation: Baudot, Wheatstone, Murray, Hughes and various applications of Morse; in fact nearly all the innovations connected with these and many other famous telegraph names were in use in the galleries of the C.T.O. Short telegraph circuits in London itself, however, gradually gave place to phonogram and telephone-telegram circuits. There was also a trend towards central-battery working and, in the C.T.O., secondary-cell batteries of ±40 volts, ±80 volts and ±120 volts replaced thousands of primary cells.

The C.T.O. had by this time achieved a status of international importance due to its size and world-wide ramifications. At a social function of the Post Office Engineering Department in 1908, the Engineer-in-Chief, Major O'Meara, claimed that the British telegraph service was acknowledged throughout the world to occupy the premier position.

This period and the ensuing few years were indeed the golden age of the C.T.O. The galleries were lofty, with good light from spacious windows. The instrument tables had none of the sleek anonymity of the modern hammer-grey metal cover; every set was individual and very impressive with a prodigious amount of lacquered brass. Sounders, keys, standard relays and indicating needles in elegant Gothic cases contributed to the variety of apparatus (Fig. 2). The whole place was alive with movement, and the hum and clatter created an atmosphere of urgency.

FIG. 2 - A SCENE IN THE C.T.O. IN THE EARLY 1900's

The operating staff included both men and women, in the ratio of about two to one, and a high standard of proficiency in keying Morse, in using the keyboard perforator and in reading Morse by sight and sound had to be attained. Considerable skill was necessary to operate the various systems at the required speed, especially the Baudot system, for which a 5-unit code had to be memorized in order to manipulate the five piano-type keys and to maintain cadence with the distributor.

The engineering staff were highly skilled mechanics rather than technicians, and had a specialized knowledge of telegraph instruments and the ability to make spare parts by hand. There was great pride of craft amongst them and they established a tradition of craftsmanship that came to be particularly associated with the C.T.O.

With the coming of the First World War, telegraph traffic increased. The Anglo-Russian cable between Peterhead and Alexandrovsk came into use and the Imperial Cable linking the C.T.O. to Halifax, Nova Scotia, was opened in 1917. In conjunction with Canadian land lines to the Pacific Cable it linked Great Britain more closely with Canada, Australia and New Zealand.

After the First World War further technical development took place, notably in the Baudot system, which gradually superseded the Hughes system on Continental circuits. Traffic at this time was approximately 45 million telegrams per year, and there were 4,500 telegraphists, of whom 2,000 were women. Including inspectors, tube attendants and messengers, the total staff was 5,700. The late twenties and the early thirties saw much change in the method of handling traffic. An 18-suit phonogram installation was brought into use and the telephone-telegram gallery, which had access to 680 telegraph offices, dealt with 50,000 messages a day.

The next development, the teleprinter, made the greatest impact of all, changing the appearance and the character of the C.T.O. completely. The Teleprinter No. 3A, a tape-printing instrument, came into use in 1928, while the year 1932 saw the introduction of a page-printing machine (the Teleprinter No. 7). The appearance of the galleries was changing; the array of brass and the impressive Morse and Baudot instruments gave way to the now familiar teleprinter on double-sided tables with a centre vee-band feeding direct to a common distribution area. The v.f. channel was also developed during this period and gradually became universal. The channel-ends were wired through jacks in the galleries to give flexibility and to facilitate the inter-connexion of circuits. Picture transmission to newspaper offices was introduced and a printergram section was opened.

The gathering war clouds of 1938 put a stop to further changes and, when war came, the inside of the great building was completely destroyed by fire in one of the heavy air raids of 1940.

Rebuilding commenced, but it was considered unsafe to utilize the outside structure higher than the first floor (Fig. 3), although another storey was added later. The new equipment, installed on a teleprinter point-to-point basis with 210 bothway phonogram positions and five concentrator switchboards, was opened for service in June 1943 and escaped the hazards of the latter period of the war.

In 1945 a manually-switched system replaced the inland point-to-point network and in the following year two prototype switchboards were installed to re-open the telex service to Europe, using exclusively telegraph channels. By 1956 the manual switching of public telegraphs was replaced by an automatic system and 90 teleprinter positions connected to this system were installed in the C.T.O.

The new manual telex service expanded rapidly and plans were, put in hand for this also to become completely automatic. In the interim period telex growth necessitated practically continuous installation of additional telex switchboard positions in the C.T.O., and the remarkable total of 242 positions dealing with approximately 2,300 subscribers and 1,200 trunks was reached. Telegraph test-desks were introduced and electronic distortion-measuring sets came into use. The peak 80 + 80-volt load had, by this time, reached 360amps - a far cry from the output of the original primary-cell batteries.

In 1960 the running down of the historic building commenced; the Cable Room with its radio circuits, multi-destination press and European point-to-point circuits was transferred to Electra House. By December 1960 all London and Home Counties telex subscribers had been transferred to the new automatic telex exchange in Fleet Building together with the major portion of the incoming continental traffic, thus enabling 82 inland telex switchboard positions in the C.T.O. to be closed. The international telex exchange, comprising 160 positions, remains to handle outgoing overseas traffic, but this exchange will also gradually close down as international subscriber-to-subscriber dialling is made available during 1961. Only a few positions will then be left in service to deal with assistance traffic and directory inquiries. These services and also the whole of the public telegraph instrument-room services will be removed to Fleet Building in 1962. When this is done the last link will be broken and a momentous chapter of telegraph history will come to an end.

FIG. 3 - THE C.T.O. AFTER REBUILDING
 

Last revised: January 22, 2024