This locomotive was a passenger prototype with Francis Webb's system of three-cylinder compound divided drive. It was built in 1885 by the LNWR's Crewe works. The design was basically derived from the 4ft 6 in tanks, so it was a tank locomotive with a leading and trailing axle with were both radially adjustable, and two driving axles. The centers of the driving wheels had a diameter of four feet and six inches and the tyres had an outside diameter of four feet and 8.5 inches.

The small outside high pressure cylinders drove the second driving axle, while the large inside low pressure cylinder drove the first driving axle. As with the earlier 2-2-2-0 Webb compounds, both driving axles were not coupled. Additionally, this locomotive was special in that the inside cylinder had a stroke of 24 inches, while the stroke of the two on the outside was six inches shorter. Both sets of cylinders had separate valve gears, so that the low pressure cylinder could completely use the exhaust of the high pressure cylinders.

Like the 2-4-2T tanks it was based on, No. 687 was used on the District Line. To be operated on the section to Mansion House, it was equipped with a condenser. In everyday service, it became apparent that the cylinder layout caused jerky movements when accelerating heavy trains. In the years to come, more 2-2-2-2T and 2-2-2-0 locomotives were built with Webb's compound system. But all of these had the same stroke for the high and low pressure cylinders.