Editing LSWR N15 class (section)

===Performance of the Maunsell batches and modifications===
The improved front-end layout applied to the first batch of "Eastleigh Arthurs" (Nos.&nbsp;E448–E457) ensured continuous fast running on flat sections of track around London, although their propensity for speed was sometimes compromised over the hilly terrain west of Salisbury.<ref name=Bradley51>Bradley (1987), p. 51</ref> The inside bearings of the Drummond "watercart" tenders proved problematic, as they were too small for the load carried and suffered from water ingress.<ref name="Haresnape55" /> The retention of the tall Drummond cab prevented use away from the Western section of the Southern Railway.<ref name="Haresnape55" /> Despite these problems, their operational reliability prompted the management to arrange the visit of No.&nbsp;E449 ''Sir Torre'' to the Darlington Railway Centenary celebrations in July 1925.<ref name=ObsBkRailways>Casserley (1952), p. 77</ref> No.&nbsp;E449 also recorded speeds of up to {{convert|90|mph|abbr=on}} on the South West Mainline near {{stnlnk|Axminster}} in 1929.<ref name=Bradley51 /> This proved that with the right components, Urie's original design could perform well.<ref name= Nock172 />

Despite the successful use of modified N15 components to rebuild Nos.&nbsp;E448–E457, the mechanically similar "Scotch Arthurs" proved disappointing when put into service from May 1925.<ref name=Bradley101 /> The performance of those allocated to the Eastern section was indifferent, and failed to improve upon the [[double-heading|double-headed]] ex-SECR [[4-4-0]]s they were to replace.<ref name=Bradley101 /> Reports of poor steaming and hot driving and tender wheel axleboxes were common from crewmen and shed fitters.<ref name=Bradley101 /> After investigation, the problems were attributed to poor workmanship during construction as the North British Locomotive Company underquoted production costs to gain the contract.<ref name=Bradley103>Bradley (1987), p. 103</ref>  Defects were found in boiler construction across the batch, and necessitated six replacement boilers, re-riveting, re-fitting of tubes and replacement of firebox stays.<ref name=Bradley103 /> The hot driving wheel axleboxes were caused by the main frames being out of alignment.<ref name=Bradley103 /> A 1926 report suggested that all affected locomotives should be taken to Eastleigh for repair.<ref name=Bradley103 /> Once repaired, the "Scotch Arthurs" proved as capable as the rest of the class in service.<ref name= Nock172 />

"Scotch Arthurs" Nos.&nbsp;E763–E772 received new tenders between 1928 and 1930 in a series of tender exchanges with the Lord Nelson and [[LSWR S15 class|LSWR S15]] classes.<ref name=Bradley109>Bradley (1987), p. 109</ref> This ensured that they could exchange their Urie {{convert|5000|impgal|L|sigfig=3|abbr=on}} bogie tenders with the {{convert|4000|impgal|L|sigfig=3|abbr=on}} Ashford design for use on the shorter Eastern section routes.<ref name=Bradley107 /> Whilst useful for the roster clerks at Battersea shed, any transfer to the Western section was hampered because of their shorter range.<ref name=Bradley107 /> By 1937, all had reverted to the Urie {{convert|5000|impgal|L|sigfig=3|abbr=on}} bogie tenders, though Nos.&nbsp;E768–E772 were attached to new Maunsell flush-sided tenders with brake vacuum reservoirs fitted behind the coal space.<ref name=Bradley109 /> These were again swapped with Maunsell LSWR-style bogie tenders fitted to the Lord Nelson class.<ref name=Bradley109 />

The second batch of "Eastleigh Arthurs" displaced the ex-[[SECR K and K1 classes|K class]] tanks and ex-[[LB&SCR H2 class|LBSCR H2 "Atlantic"]] [[4-4-2 (locomotive)|4-4-2]] locomotives on the {{stnlnk|Eastbourne}} and {{stnlnk|Bognor Regis}} routes respectively.<ref name=Bradley107 /> They were well liked by crews and used on this part of the network until the arrival of electrification.<ref name=Bradley118 /> No.&nbsp;E782 ''Sir Brian'' was used on the former [[Great Northern Railway (Great Britain)|Great Northern]] main line for performance trials against the SECR K and K1 class tanks following the [[Sevenoaks railway accident]] in 1927.<ref name=Pringle36>Pringle (1928), p. 36</ref> The tests were supervised by the [[London and North Eastern Railway]]'s CME, Sir [[Nigel Gresley]], who commented that the class was unstable at high speeds.<ref name=Pringle37>Pringle (1928), p. 37</ref> The instability was caused by motion hammerblow and exacerbated by irregularities in track-work.<ref name=Pringle36 /> This caused excessive stress to the axleboxes and poor riding characteristics on the [[footplate]].<ref name=Haresnape52>Haresnape (1983), p. 52</ref> Despite this, the class benefited from an excellent maintenance regime.<ref name=Bradley118>Bradley (1987), p. 118</ref>

Maunsell's successor [[Oliver Bulleid]] believed that there was little need to improve draughting on this series. However, reports of poor steaming with No.&nbsp;792 ''Sir Hervis de Revel'' gave him an opportunity to trial a Lemaître multiple-jet blastpipe and wide-diameter chimney on a Maunsell N15 in 1940.<ref name=Bradley123>Bradley (1987), p. 123</ref> This did not enhance performance to the extent of No.&nbsp;755 ''The Red Knight''.<ref name=Bradley123 /> Under British Railways ownership, the locomotive was re-fitted with the Maunsell chimney in March 1952 with no further problems reported.<ref>Bulleid, H.A.V. (1979) – for information on Oliver Bulleid's modifications.</ref> In another wartime experiment, Bulleid fitted No.&nbsp;783 ''Sir Gillemere'' with three thin "stovepipe" chimneys in November 1940.<ref name=Haresnape61>Haresnape (1983), p. 61</ref> These were set in a triangular formation to reduce visibility of exhaust from the air in response to attacks made by low-flying aircraft on Southern Railway trains.<ref name=Bradley123 /> The "stovepipes" were reduced to two,  producing a fierce exhaust blast that dislodged soot inside tunnels and under bridges.<ref name=Haresnape61 /> The experiment was discontinued in February 1941 and the locomotive re-fitted with a Maunsell King Arthur chimney.<ref name=Bradley123 /> The last experiment was with spark-arresting equipment in response to lineside fires caused by poor quality coal.<ref name=Bradley124>Bradley (1987), p. 124</ref> Nos.&nbsp;784 ''Sir Nerovens'' and 788 ''Sir Urre of the Mount'' were fitted with new wide-diameter chimneys in late 1947.<ref name=Bradley124 /> Test-trains showed mixed results and the trials were stopped in 1951 after improvements in coal quality and the fitting of internal smokebox spark-arrestors.<ref name=Bradley124 />