Thomson Marconi Sonar (TMS) was formed as Ferranti Thomson Sonar Systems (FTSS) in 1990 by the merger of the sonar systems businesses of Thomson-CSF and Ferranti. The head office of FTSS was at Cheadle Heath, Stockport, with subsidiary sites in Church Crookham, Hampshire, Weymouth, Dorset, Bridlington, Yorkshire and Rochester. GEC acquired Ferranti's share of the business in 1995 to form Thomson Marconi Sonar.
With the merger of GEC's defence business Marconi Electronic Systems and British Aerospace in 1999, the resulting BAE Systems acquired Marconi's 49.9% share in TMS. In 2001 Thales announced the completion of the acquisition of BAE Systems' share in Thomson Marconi Sonar (TMS). Thomson Marconi Sonar was renamed Thales Underwater Systems and became part of Thales' Defence business.
The deal makes Thales the sole shareholder of Thales Underwater Systems. Thales Underwater Systems has operating units in France, the United Kingdom and Australia, employing more than 2,500 people world-wide and generating sales in 2000 of 345 million Euro.