The manufacture of telecommunications equipment in the United Kingdom dates back to the 1880s. With the municipalisation and eventual nationalisation of telecommunications, it was the Post Office that had responsibility for research and development of new systems until the 1980s. After the Second World War it had opted to remain with an older technology and later waited for digital exchanges, known as System X supplied by GEC and Plessey, while STC (part of ITT) supplied the analogue TXE4. With the introduction of competition BT felt it should benefit, purchasing some exchanges from Ericsson, through a joint venture with UK-based Thorn-EMI. After GEC was refused permission to acquire Plessey, GEC and Plessey merged their telecommunication manufacturing interests as GPT, soon taken over by a GEC and Siemens joint venture. GEC spun off its defence interests, rebranded itself Marconi and bought Siemens out of GPT, but made very bad acquisitions in the US. In the aftermath of the dot com crash Marconi fell into serious difficulties, then when it was rejected as a supplier for the BT 21st century network (21CN) it sealed the fate of Marconi, which was to be acquired by Ericsson. No firm was successful in entering the market for mobile telephone systems.