Ferranti Thomson Sonar Systems (FTSS) was established in 1990 by the merger of the sonar systems businesses of Thomson-CSF and Ferranti, initially under the name Thomson Marconi Sonar (TMS). 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. In 1999 BAe Systems was formed out of a merger of GEC's defence business Marconi Electronic Systems and British Aerospace, with the new company acquiring Marconi's share in TMS.

In 2001 Thales acquired BAE Systems' share in Thomson Marconi Sonar (TMS), and Thomson Marconi Sonar was renamed Thales Underwater Systems.