HS4000 Kestrel was a prototype high-powered mainline diesel locomotive that was built in 1967 by Brush Traction, Loughborough, as a technology demonstrator for potential future British Rail and export orders. The locomotive number is a combination of the initials of Hawker Siddeley (the owners of Brush Traction) and the power rating of its Sulzer diesel engine (4,000 hp), making it the most powerful locomotive built by the company. It was of Co-Co wheel arrangement and was fitted with a Sulzer 16LVA24 engine rated at providing a maximum speed of and weighed 133 tonnes. It was painted in a livery of yellow ochre with a broad chocolate-brown band around the lower bodyside separated by a thin white line running around the body. Background and design In the mid 1960s British rail produced specifications for type 5 locomotives weighing less than 126 tonnes with more than of power for both passenger and freight working. Brush Electric Engineering Ltd. (Brush Traction) in association with Sulzer Brothers Ltd. responded with a locomotive for British Rail's appraisal. The body, exterior details, control console, and colours were designed by E.G. M. Wilkes of "Wilkes & Ward" (later Wilkes & Ashmore, industrial design firm based on Horsham, West Sussex). The design principle was that a single engine would require less maintenance than twin-engined vehicles, and that the very high power would mean that double heading for freight trains would be unnecessary. Diesel engine Brush employed Sulzer's 16-cylinder Vee 16LVA24 engine made in Winterthur. Previous experience with Sulzer's 12-cylinder twin parallel-bank dual-crank 12LDA28 engine had gone well, but the highest power available from Sulzer in this form was the 12LDA31 of . Not only did the V engines provide over , but being single-crank with the consequently lighter engine block (over the dual-bank design) gave a better power-to-weight ratio. The engine is a four-stroke turbocharged oil-cooled design, with the oil being cooled by water in a heat exchanger, and the water cooled in radiators. The piston diameter is 240 mm with a stroke 280 mm. A smaller auxiliary generator (~40 kW) was used to charge the batteries or start the engine etc. Electrical transmission and auxiliary electrical system To transmit this power to the rail Brush utilised a brushless salient pole three phase alternator connected to a rectifying circuit of 84 silicon diodes producing ~2,500 kW of power for electric traction from the diesel engine. An auxiliary alternator,