From Wikipedia: Marconi Electronic Systems:
Marconi Electronic Systems (MES), or GEC-Marconi as it was until 1998, was the defence arm of The General Electric Company (GEC). It was demerged from GEC and acquired by British Aerospace (BAe) on November 30, 1999 to form BAE Systems. GEC then renamed itself Marconi plc.
MES exists today as BAE Systems Electronics Limited, a subsidiary of BAE Systems, but the assets were rearranged elsewhere within that company. MES-related businesses include BAE Systems Submarine Solutions, BVT Surface Fleet, BAE Systems Insyte and SELEX Sensors and Airborne Systems (now owned by Finmeccanica).