page_title: SR Merchant Navy class
section_title: Modification
hierarchical_section_title: SR Merchant Navy class / Modification
caption_attribution_description: Merchant Navy Class &quot;Clan Line&quot; 35028 reversing at Swindon
context_page_description: The SR Merchant Navy class is a class of air-smoothed 4-6-2 Pacific steam locomotives designed for the Southern Railway by Oliver Bulleid. The Pacific design was chosen in preference to several others proposed by Bulleid. The first members of the class were constructed during the Second World War, and the last of the 30 locomotives in 1949.
  Incorporating a number of new developments in British steam locomotive technology, the design of the Merchant Navy class was among the first to use welding in the construction process; this enabled easier fabrication of components during the austerity of the war and post-war economies. In addition the locomotives featured thermic syphons in their boilers and the controversial Bulleid chain-driven valve gear. The class members were named after the Merchant Navy shipping lines involved in the Battle of the Atlantic, and latterly those which used Southampton Docks, a publicity masterstroke by the Southern Railway, which operated Southampton Docks during the period.
context_section_description: Partially because of the Crewkerne incident, and due to the incessant modification of Bulleid's original design, British Railways took the decision to rebuild the entire class to a more conventional design by R. G. Jarvis, adopting many features from the BR 'Standard' locomotive classes that had been introduced since 1950. The air-smoothed casing was removed and replaced with conventional boiler cladding, and the chain-driven valve gear was replaced with three separate sets of Walschaerts valve gear. The rebuilds were provided with a completely revised cylindrical smokebox, a new Lord Nelson-type chimney and LMS-style smoke deflectors. Together with the lack of air-smoothed casing, these helped reduce the problem of smoke and steam obscuring the driver's vision of the line.
  The fast-moving and unpredictable Bulleid steam reverser was replaced with a screw-link version, whilst the mechanical lubricators were moved to the footplates along the boiler sides. Sanding was also added to the leading driving axle, whilst rearward application was incorporated to the middle driving axle. The first 'modified' locomotive to be released from Eastleigh was 35018 British India Line in 1956. The final example, 35028 Clan Line, was completed in 1960. The success of the modification programme for the Merchant Navy class was also to influence the design of the future modification of 60 'Light Pacifics'.
caption: 35028 "Clan Line" as modified without the air-smoothed casing and with Walschaert's valve gear
exif: {}