After several unsatisfactory trials of petrol engined traction on the Welsh Highland, a idea of a trial of a diesel locomotive was attractive, and at the suggestion of Lt.Col.Stephens, Kerr Stuart offered the locomotive for for trials on the Welsh Highland Railway . 4415 was ordered in May 1928 and arrived at Dinas just three months later in July 1928.
|KS 4415 on trial at Dinas|
On 15 November 1928 a Press & Publicity day was held at Dinas, attracting widespread coverage (see separate article). Drawgear was borrowed from single Fairlie 'Moel Tryfan' and the lack of vacuum brake equipment on the locomotive was quietly ignored.
Early in 1929 suitable drawgear and vacuum brakes were fitted to enable working of the thrice-weekly winter service between Dinas and Beddgelert.
In March 1929 it was transferred to more lucrative work on the Ffestiniog Railway shunting slate trains, and in the process had its roof lowered.
Despite its satisfactory performance, the Ffestiniog Railway Company had to return the locomotive to Kerr Stuart in August 1929 as they were unable to afford to purchase it.
It went on a further trial to Sir Lindsay Parkinson & Sons who were constructing the East Lancs Road between Liverpool and Manchester. (The late Tom Rolt, who accompanied the loco, said that it was never used here as it was too heavy for the track.)
In December 1929 it was regauged to 3'0” and sent to the Castlederg & Victoria Bridge Tramway in Co.Tyrone, Northern Ireland, where it stayed for about six months although seeing little use as it was not powerful enough for duties on the tramway.
Kerr Stuart went into liquidation in 1930 on account of misappropriation of funds by the Company chairman, and the loco was acquired by Hunslets. In March 1934 it was re-gauged back to 2ft and sold by their agents Robert Hudson for use on a sugar plantation railway in Mauritius.