HS4000, named Kestrel, was a prototype high-powered mainline diesel locomotive 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 the owner of Brush Hawker Siddeley and the power rating of its Sulzer diesel engine (4000 HP).
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 125 mph (201 km/h) 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.
The locomotive was sold to the Soviet Union in 1971 for £127,000, being shipped from Cardiff Docks to St Petersburg docks by the MV Krasnokamsk in July 1971. The locomotive was regauged to 1520 mm, and tested on a circular test railway as well being used on some parts of the Russian rail network.
After testing of the locomotive the engine was removed for static testing, and the locomotive body ballasted for use in high load tests of other vehicles.
The remains of the vehicle are believed to have been scrapped in 1993.