classes classes consisted steam locomotives wheel arrangement built claims fame inside cylinder run great_britain locomotive involved bridge disaster rebuilding compound expansion locomotive tandem compounds britain intended express passenger trains routes handled trains london edinburgh began heavier trains locomotives capabilities removed line service line rebuilt remained service history locomotive superintendent start february tenure seven years provided new locomotives suitable hauling express passenger trains built class considered good engines followed nos built locomotive works locomotives formed class leading chosen sharp curves wheels small diameter solid centres centre fixed opposed adams type later coupled wheels diameter principal dimensions cylinders diameter stroke coupled inside frame inside cylinder run great_britain class years introduced july layout inside frames inside cylinders widespread great_britain great western railway main line company eventually possess type earlier designs railways outside cylinders nos built outside frames class express passenger trains route edinburgh line edinburgh glasgow days construction forth bridge isolated system class followed locomotives class nos differed class respects wheels diameter instead coupled instead dome mounted boiler barrel instead rear wheel shaped wheel instead square topped intended use route increase traffic anticipated midland railway time building settle line route open english traffic entirely hands london worked closely tandem main rival trains route comparatively light capabilities class opened settle line service route london introduced time north trains operated route company locomotives respective lines initially locomotives class equipped brake locomotives cost engine brake carriages fitted locomotives proved powerful second engine needed assist climbing particularly junction successor offered opinion express locomotives period like chickens legs wings result designed new class class began displace trains capable maintaining schedule min miles intermediate stops class remained route local trains lighter trains england bridge disaster opening forth bridge passengers edinburgh cross ferry connected trains north trains travel onward december regular engine mail train class failed based spare time called work train incident southbound run working northbound service later day arrive little bridge shortly collapsed driver warning impending disaster closed applied brakes persons killed despite fall locomotive relatively undamaged protected bridge formed cage train fell april attempt recover locomotive failed chains broke days later second attempt failed salvage equipment broke locomotive brought surface week later recovered stood bank sent wheels repairs returned traffic gained nickname result accident difficult recovery drivers refused second bridge built new design opened 29th anniversary disaster december sunday evening mail bridge rebuilding locomotive superintendent rebuilt cylinder tandem compound form low pressure cylinders diameter mounted position previously occupied original cylinders centre high pressure cylinders diameter inches placed common stroke remained engine given modified form joy valve gear boiler pressure pounds square inch kpa area chief features design patented cousin holmes entirely successful somewhat better british tandem compounds nos tandem compound system widely usa russia rebuilt simple expansion form locomotives generally rebuilt boilers wore received new boilers course life fitted holmes holmes ultimately rebuilt locomotives nos rebuilt nos received rebuilding later years secondary branch line trains final years months renumbered older locomotives duplicate list order vacate numbers new construction accordingly nos placed duplicate list nos respectively nos similarly treated order withdrawn service following nos classes completely withdrawn grouping locomotives wheel arrangement passed london company formed start amalgamation railways number plate tender preserved summary locomotives named stated replaced named engines including service
NBR 224 and 420 Classes