The de Havilland Engine Company's portfolio included the (licensed) Gnome turboshaft.

Bristol Siddeley was bought by Rolls-Royce Limited in 1966 for £63.6 million in order to prevent competition from a planned collaboration between BSEL, Pratt & Whitney and Snecma.

Outside the aeronautical field its products were gas turbines for marine and industrial use, diesel engines, and automatic transmissions.

The Patchway factory in South Gloucestershire produced military aeroplane engines including the Olympus two-spool turbojet (from which the engine for Concorde was developed), the Orpheus turbojet for the Folland Gnat light fighter/trainer aircraft, the Pegasus two shaft medium bypass ratio vectored thrust turbofan for the Hawker Siddeley P.1127/Kestrel/Harrier VSTOL ground attack aircraft, the Proteus turboprop for the Bristol Britannia airliner and the Viper turbojet for the Hawker Siddeley HS.125.

High supersonic ramjets for long range defensive missiles were tested in the HATP (Ref TJ102 and TJ151/2).

Bristol Siddeley also manufactured diesel engines under licence from the German company Maybach.

[citation needed] The Maybach Diesel (MD) MD650, MD655 and MD870 series engines built by Bristol Siddeley were sophisticated in design, running at much higher speeds than normal diesels of their size and featured advanced construction such as a disc-webbed crankshaft that ran in large roller bearings, telescopic pipes to deliver cooling oil to the pistons and detachable piston crowns.

They were used with hydraulic transmission systems, in the Type 4 locos (with two MD650 engines of 1,152 bhp each) hauled the express trains of the Western Region of British Railways - e.g. the Bristolian and the Cornish Riviera.

[9] Subcontracted production of the Sunbeam Alpine sports car continued at Bristol Siddeley Engines in Coventry until 1962.