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The network expands

A rural automatic exchange (RAX) also brought with it a telephone kiosk and, if necessary, its own electricity supply. This example at Stottesdon had its own generator.

Round the clock service : open all hours

By the 1930s, rural automatic exchanges were opening at the rate of one a day, bringing with them 24-hour service to even the most remote of communities.

Originally many of the smaller local manual exchanges often had advertised hours. Operators would stop working at night, so there would often be no service after 10pm. And some operators were allowed time off on Sunday morning to go to church, so there would be a break in service.

24-hour service in such areas started only once a rural automatic exchange was introduced and if customers needed an operator they'd now get the one at the nearest town exchange. And previously unconnected villages went straight to 24-hour service. 

1940s GPO publicity poster

Meeting increased telephone demand : struggling to meet demand

Technical factors mean telephones work better when close to exchanges. A current example is the difficulty of providing service to customers more than about two miles from the exchange.

It was the building of additional exchanges that determined the speed and extent of provision of telephone lines and services during the century following 1876.

There were few problems up to the 1940s. First private companies and then the Post Office were prepared to invest in the telephone network and rising revenues ensured that costs were covered.

The problems began after the Second World War, when public investment began to drop but demand was rising fast with new housing and population shifts.Vital post war defence expenditure and the need to divert production for export made it difficult to find the money or equipment to build and equip those vital new exchanges.

Map of London Exchange names (Eastern), 1920s

Disputes over exchange name allocation : what's in a name?

In preparation for the 'dialling of London' - the switch to automatic exchanges in the 1920s - the Post Office had to assign three-letter codes to each exchange. This was a straightforward process of taking the first three letters of the area name, such as HAM for Hampstead and KEN for Kensington. Problems arose if areas shared the same three letters, such as Woodford and Woolwich. So Woodford became BUCkhurst, Hammersmith became RIVerside and Golders Green became SPEedwell.

Sometimes the name allocations caused disagreement, not least when an exchange served more than one distinct locality. On such occasions a non-specific name would be allocated, such as for the Bethnal Green exchange area - which was proudly served by ADVance.

When the old Walthamstow manual exchange came to be closed down, the plan was to transfer its lines to automatic service on the adjacent LEYtonstone unit, but many of the affected subscribers were less than overjoyed at being allocated Leytonstone numbers. They created such a fuss that the Post Office agreed to give them a new exchange. It was called it KEYstone, and everyone was happy. KEYstone and LEYtonstone numbers were actually one and the same - both were dialled as 539 - but customer sensitivities had been appeased, and the Post Office had hardly had to change its plans at all.

Diagram from a customer leaflet illustrating the face of a lettered dial

Exchange names : turning numbers into names

When automatic exchanges and dial telephones were introduced into London, it was decided that all figure numbers would be less memorable than giving each exchange a 'name' with a three letter code.

The telephone dial had ten numbers, from 1 to 0, and there were 26 letters to fit into the available holes.

But it was more complicated than that - the letter O was allocated for the Operator, so that was the zero hole spoken for. Also, engineers had avoided numbers beginning with 1 since the start of automatic exchanges in 1912. This is why customer telephone numbers still never begin with 1, and is why there were - and still are - no lteers associated with the digit.

That left 8 numbers (2-9) to cover 23 letters, with Q and Z considered unnecessary.

(It also reduced the number of available exchange codes from a possible 1000 to a theoretical total of just 649 - and not all of those could be represented by pronouceable words. For example, the digit sequence 556 has no usable letter equivalent).

Cigarette Cards - from the BT Archives

Cigarette cards (1930s) : no smoke without wires

For the first 40-odd years of the 20th century cigarette cards were prized and collectable items. The cards were found in packets of cigarettes and carried a range of photographs and pictures on topics of general interest. In the days before specialist magazines they were a handy way for someone to build up their general knowledge.

In the 1930s Lambert & Butler issued this set of 50 cards about the Post Office. The images ranged from a policeman standing beside a call-pillar to the switchboard of an international exchange.

The cards were given away as free gifts, in the hope that smokers would stick with a particular brand in their efforts to build a complete card set. It was one way for people to learn something new about the world around them but, with the subsequent proof that smoking is potentially lethal, perhaps not the most healthy.

Front page of customer literature titled Sharing a Telephone Line

Shared service lines : Let's party!

'The local loop' is the technical expression denoting 'last leg' of the telephone network - the line that connects people's homes and offices with the exchange. In relative terms, this is a very expensive element of the network to build, costing about the same to construct and maintain as the trunk network but carrying much less traffic.

In the pioneering days of telephone, the operators' solution to the local loop issue was to make one line serve a lot of people - by making them share it.

As the telephone service extended into country areas in the 1920s and 1930s, the Post Office provided 'Rural Party Lines'. These provided a single line that was shared by up to 10 farms or cottages(which could cause problems when you wanted to use the phone at the same time as your neighbour).

A more typical form of shared-service - used until well into the 1970s - was a two-party system. Many suburban neighbours had service provided this way, slightly cheaper than 'exclusive service', of course.

Mobile exchange - a Connected Earth artefact, now at the Avoncroft Museum

Mobile telephone exchange (around 1971) : providing vital relief

With the vision of war looming and the pressure on overworked exchanges growing, the GPO rolled out its first batch of mobile telephone exchanges in April 1939.

Mobiles could relieve existing exchanges requiring additional capacity, or else were used to replace damaged exchanges. They were also used to provide temporary or interim service at locations having no exchange at all.

This particular example was part of a second fleet launched in the 1971, at a time when vast numbers of people wanted to come on the telephone for the first time. It travelled around the country, moving to another location once the permanent exchange had been built or expanded.

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The UK's first permanent gallery dedicated to the history of information and communication technologies opens in the new Information Age gallery at London’s Science Museum.

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100 years of automatic switching!
In 1912 the GPO installed Britain's first automatic telephone exchange in Epsom.

Discover the early days of the telephone...