Grace's Guide is the leading source of historical information on industry and manufacturing in Britain. This web publication contains 143,388 pages of information and 230,040 images on early companies, their products and the people who designed and built them.
of Strowger Works, Liverpool.
ATM Trade Mark.
1920 Public company formed
1936 International Automatic Telephone Co took over the business, assets and liabilities of its wholly owned subsidiary Automatic Electric Co Ltd. Name changed to Automatic Telephone and Electric Co Ltd.
WW2 development activities included Distant Reading Compass, Automatic Pilot, aircraft wiring and other electrical equipment, in addition to telecommunication engineering and production.
By 1949 wholly-owned subsidiary companies included:
1959 Automatic Telephone and Electric Co became the prime contractor for a new UK air defence system, under the code name Project Linesman. The best staff from ATE Edge Lane were moved to a new building in Cheapside in Liverpool city centre; to maintain secrecy, this was called Exchange Works. Young employeees were granted exemption from conscription. The task was to design and manufacture the data processing system for Linesman, which meant designing the system, designing the computers, developing software (which included a new high level language) and manufacturing the hardware (something like 1,000 racks of equipment). The first computer was developed with RSRE Malvern using neon tubes and valves. This was later developed into the XL2 (the XL standing for Exchange Laboratories) built entirely of germanium transistors and using a computer language developed at Exchange Works in the 1950s and 60s. The finished data processing system was installed at West Drayton; this used the XL4, a more powerful machine, and a few XL6 machines developed later. The radar was by Metropolitan-Vickers and Marconi. The secure status of the factory later attracted other secret contracts (under Plessey) and led to it becoming one of the major designers and manufacturers of cryptographic equipment.
1960 New products being developed outside the traditional areas of business but based on the telecommunications expertise of the company, with applications in road and air traffic control, data processing, instrumentation
1960 A consortium of AEI, Automatic Telephone and Electric Co, Ericsson TelephonesLtd, GEC, Marconi's Wireless Telegraph Co, Plessey Co and STC formed a holding company Combined Telephone Holdings only days after its members had failed in their bid to acquire Telephone Manufacturing Co. Combined Telephone Holdings purchased for cash more than half of the shares in Phoenix Telephone and Electric Works and offered to purchase the rest.
1961 Manufacturers of radio, telephone and telegraph equipment; thermionic devices including midget valves; telephone and mine signalling equipment; plastic mouldings; precision tools and sale of internal telephone and public address systems. 12,500 employees. 
1961 Merged with Plessey and the Ericsson Telephones. As a result, Plessey doubled in size, becoming Britain's largest manufacturer of telecommunications equipment (including the majority of the country's crossbar switches / exchanges).
As Linesman was being completed Plessey developed a silicon based computer, XL9, for commercial use, using the mini-Coral language; this was sold to various users including for a wide area traffic light control in Liverpool, an air defence system for Burma, a message switch comprising five XL9s together with lots of communications interfaces for GCHQ, and an accounting system for the GPO for a West London telephone exchange. This was followed by XL12, a really powerful computer, development of which was halted when ICL ?? was formed. Having determined there might be a requirement for a new telecoms computer, development restarted on a computer aimed at the telephone exchange market, specifically for the Australian market. Three computers, manufactured at Exchange Works, working in a redundant system were successfully demonstrated. These were quite unusual as their instruction sets were designed around the requirements of a telephone exchange. Immediately after this, the PP250 was designed, aimed at military communications systems. These were manufactured at the new Plessey Christchurch site for the Ptarmigan communications system.