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.

[7][8][9] It was of Co-Co wheel arrangement and was fitted with a Sulzer 16LVA24 engine rated at 4,000 horsepower (3,000 kW) providing a maximum speed of 110 mph (180 km/h)[note 3] 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.

In the mid-1960s British rail produced specifications for type 5 locomotives weighing less than 126 tonnes with more than 3,000 hp (2,200 kW) of power for both passenger and freight working.

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.

[1][2] A Warren truss body construction with welded, stressed steel skin was used on the sides of the locomotive which supported the transverse load of the main engine entirely.

The lighter construction and traction motors helped but the attempt was ultimately unsuccessful leaving Kestrel at 22.5 tons per axle.

Kestrel continued to be used but the axle-weight problem contributed to the decision to sell the locomotive and prior to this, in March 1971, the original bogies were refitted.

[1] On arrival in Russia, Kestrel was exhibited at the Moscow Rolling Stock Exhibition and then was moved to the All-Union Rail Transport Scientific Research Institute at Shcherbinka[14] where it was re-gauged to 1,520 mm (4 ft 11+27⁄32 in), and tested on a circular test railway[note 7] as well as being used on some parts of the Russian rail network.

[19] Heljan of Denmark have produced a highly detailed OO scale model of the Kestrel, as part of a limited run of 4000 units.