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Dorman, Long and Co of Middlesbrough were a major manufacturer and fabricator of steel components and structures.
The firm began as an iron and steel works manufacturing bars and angles for ships. A natural progression from this was to become involved in the construction of bridges, particularly when Dorman Long took over the concerns of Bell Brothers and Bolckow, Vaughan and Co in the late 1920s. 
1837 The first Cleveland ironstone mine opens, at Grosmont.
1841 Bolckow, Vaughan and Co open the first ironworks in Middlesbrough.
1855 30 blast furnaces operate within six miles of Middlesbrough.
1865 One million tonnes per annum (TPA) of iron were produced to make the area one of the world's major centres of iron production.
1875 Number of blast furnaces increased to 100, producing two million tpa.
1876 Dorman, a metal broker, launched a partnership with Albert de Lande Long, taking over an existing plant, the West Marsh ironworks, Middlesbrough, initially manufacturing iron bars and angles for shipbuilding.
1879 Sidney Gilchrist Thomas persuaded E. W. Richards, manager of Bolckow, Vaughan and Co's works, to try out the process that he and his cousin, Percy Gilchrist, had invented for dealing with the phosphorus in pig iron produced by the Bessemer converter leading to the commercial production of steel.
1882 The firm purchased the Britannia Works from Sir B Samuelson
1880s the firm switched to the new steelmaking technologies, installed open-hearth furnaces and exploited the breakthroughs of Gilchrist and Thomas
1889 The company was registered on 2 November, to take over the business of manufacturers of iron and steel bars of the firm of the same name at Middlesbrough-on-Tees, and other businesses have since been acquired.  Operated the Britannia Works and the West Marsh Works.
1891 William Henry Panton was appointed general manager
1900 Obtained the contract for the new construction works for The Westinghouse Electric and Manufacturing Co to be erected at the Trafford Park Estate on the Manchester Ship Canal. They also have a contract for similar work for the British Thomson-Houston Company's new works to be erected at Rugby.
By 1901 the company was a major manufacturer with a labour force of about 3000 and an output of about 180,000 tons of finished material a year.
1901 For a topical overview of the company's works see The Engineer 1901/05/31
1902 The first integrated steelworks, involving conversion of iron ore to finished rolled steel shapes, was built at Cargo Fleet.
By 1914 Dorman Long had a workforce of about 20,000 and was a dominant firm on Teesside and a major British steel producer.
1914 Directory: Steel Manufacturers of Port Clarence, Middlesbrough. 
1914 Steel manufacturers, bridge builders and constructional engineers, manufacturers of rolled steel girders and all descriptions of sectional steel for shipbuilding, bridge building etc., steel rails and billets, galvanized corrugated sheets and steel wire of all classes. 
WWI Major supplier of shells. Started to construct a £4.5 million plant at Redcar, Yorkshire,
1917 The new Redcar steel plant was opened, making steel in the 'open hearth' process. A garden village, Dormanstown, was constructed for the workers using steel-framed housing
1917 Acquired Newport Ironworks
1918 Cleveland Works opened.
1922 Dorman Long and Co won the contract to build the Sydney Harbour Bridge.
1923 The Subsidiary companies were liquidated and the assets transferred to Dorman Long
1924 December: won the contract to build the Tyne Bridge, Newcastle
1927 See Aberconway for information on the company and its history.
Over-capitalized and burdened with debts, Dorman sought refuge in another merger with an equally ailing neighbour, Bolckow Vaughan.
1929 Acquired Bolckow, Vaughan and Co; the latter controlled Redpath, Brown and Co; the bridge-building and structural engineering parts of Dorman together with the Redpath business would assume a commanding position in structural engineering.
1934 Built the Tees Vertical Lift Drawbridge.
1946 Dorman Long and Co purchased 600 acres of land between the Redcar and Cleveland Works to build the Lackenby development.
1947 Civil engineering work had been done at the site at Lackenby but construction of the new plant had not started by the end of the year. It was planned to build 2 new blast furnaces at the Cleveland Works.
1949-59 Built railway locomotives. 
1954 Dorman Long and Company became a holding company on 2 October. The Holding and Realization Agency sold all of the shares in the company to the public. Operating activities transferred to 3 subsidiary companies; Dorman, Long (Steel), Dorman, Long (Bridge and Engineering) and Dorman, Long (Chemicals)l subsidiaries were Redpath, Brown and Co, Tees Side Bridge and Engineering Works, British Structural Steel Co and Dorman Long (Africa)
1956 Annual meeting told about performance of the main subsidiary companies:
1967 Became part of British Steel.
1973 Site development of the existing Redcar Ironworks began.
1973 British Steel sold its carbon- and mild-steel wire-making activities at Warrington (Rylands and Whitecross) and at Middlesbrough (Dorman Long) into a new company Rylands-Whitecross, jointly owned by Tinsley Wire Industries and British Ropes
1979 The number of blast furnaces drops to one - producing 3.3 million TPA.
1990 they were merged with the Cleveland Bridge and Engineering Co and were still involved in the design, manufacture, fabrication and erection of many different types of structures such as bridges, buildings, offshore platforms, airports, etc, with one of the most recent high profile contracts, being the new Wembley Stadium in London, England.
2000 Formed in this year and now called Dorman Long Technology, based in Northants 
"Dorman Long, founded in 1876, became a public company in 1889. It grew by a series of amalgamations which absorbed such famous names in the British iron and steel industry as Bell Brothers and Bolckow Vaughan. The first company in Britain to roll steel joists (in 1883), Dorman Long (Steel) Ltd. is the largest producer in the United Kingdom of steel for the structural industry. The company is responsible for approximately 9% of the steel output of the country and has a capacity of 2·6 million ingot tons per annum. Today it operates four steelworks, a wire works, a sheet works and a plastic-coated sheet plant.
In addition to universal beams and columns, Dorman, Long (Steel) produces heavy and medium plates, heavy joists and sections; rails, sleepers, light sections and bars; wire rod, wire; mild steel, black, galvanised and plastic-coated sheets; and welded steel fabrication.
Since 1945 Dorman Long have spent virtually £100m. on capital development, the outstanding feature of which has been the installation of a universal beam mill at the Lackenby Works where there is also a continuous billet mill and a rod mill. In December, 1963 a stabbing and blooming mill was brought into operation to serve a new universal plate mill, now under construction at Lackenby together with a new rod mill. The whole of the company's iron making is now concentrated at the Clay Lane blast furnace plant where three furnaces of 1,500 tons per day nominal capacity are in operation.
At the turn of the century a bridge and constructional department was created and the Dorman Long Structural Group today is responsible for approximately 22% of the steel structural engineering industry of Great Britain. It has built many famous bridges in different parts of the world and its other structural activities cover the construction of factories, power stations, multi-storey buildings and similar type of structures.
On the north bank of the Tees, at Port Clarence, Dorman Long (Chemicals) Ltd. operate an important chemical plant where crude tar and benzole from the South Bank Coke Ovens are refined to produce a variety of chemical products.
All the company's works are situated on the banks of the River Tees, affording exceptionally good facilities for the discharge of foreign ore and fuel oil, and the export of finished products. The Dorman Long Group, including its overseas structural-engineering companies, today employs 25,000 people."