The H15 class represented Robert Urie's first design for the LSWR. It was created in response to a desperate lack of adequate locomotives in service on the LSWR that could be utilised for heavy freight duties. Reliability was also an issue, with ageing locomotive designs taking their toll on the LSWR's resources. Ten locomotives (numbers 482–491) were built new by
Eastleigh Works with boilers. They appeared in January to July 1914. Urie was a proponent of
superheating, so in order to gain experience and data on performance and fuel economy, four of the locomotives (482–485) were fitted with
Schmidt superheaters, four (486–489) with
Robinson superheaters, and two (490–491) were built as saturated locomotives. The last two had a lower weight than the first eight. While the data gained from this small experiment showed the benefits of superheating, neither design of superheater was deemed suitable by Urie, so he designed and patented his own: the
Eastleigh superheater, An additional locomotive was a rebuild of the 1905
E14 class No. 335 undertaken in December 1914. The locomotive had been scheduled for major modifications by Urie's predecessor
Dugald Drummond in the light of poor operational performance. However, improvements were made to the overall design whilst the locomotive was under production at
Eastleigh Works. The earlier class members mounted a lower running plate that was raised above the cylinders for clearance. These locomotives also sported a single, straight splasher above the driving wheels, an embellishment that would feature on Urie's later
N15 class. The later production locomotives did not feature this design, with a higher-mounted straight running plate above the driving wheels, a feature that was perpetuated on the later
S15 class design by Urie. A total of 26 locomotives were completed in six batches, including number 335, over a period of twelve years. The first two batches of five in each were constructed in 1914. A further fifteen locomotives were constructed in three consecutive batches during 1924, the final one appearing in January 1925, and these were constructed under the auspices of Richard Maunsell, Urie's successor. Amongst the final batches of the class was another rebuild project concerning five members of the Drummond F13 Class. Maunsell's own batch of ten locomotives were a continuation of the design set out by Urie with number 491. The class was provided with a 5,000 gallon Drummond 'watercart' eight-wheeled tender design that enabled them to travel on the long distances of the LSWR network which never had water troughs. Further modifications to the class were made by Maunsell during the mid-1930s with the provision of smoke deflectors. == Operational details ==