3901 Class O2/2 'Tango' BR Late Crest Black No.63937 (GN Cab/LNER Flush-Sided Tender) Steam LocomotiveIntroduced by the Great Northern Railway in 1921 to a design by Sir Nigel Gresley, these powerful 2 8 0s were built to haul heavy coal and ironstone trains. Several batches were built over a 22 year period by the Great Northern Railway (GNR) and LNER, with numerous improvements such as better cabs and bigger tenders. Heljan's models depict the O2 1, O2 2 and O2 4 variants with the previously unreleased GNR style cabs (original high style and reduced