 Like BAC, the Hawker Siddeley Group was expanded by merger, while engine design and manufacturing was concentrated at Rolls-Royce and the newly formed Bristol-Siddeley Engines.Helicopter development was given to Westland Helicopters.On 29 April 1977, BAC, the Hawker Siddeley Group and Scottish Aviation were nationalised and merged under the provisions of Aircraft and Shipbuilding Industries Act 1977.