The LNER Gresley O2 Class “Tango” 2-8-0 locomotives were heavy freight engines designed by Sir Nigel Gresley for the London and North Eastern Railway in the early 1920s. Built mainly at Doncaster, they were intended for coal and mineral traffic on demanding routes such as the Great Central main line. Their long boiler and wide firebox gave strong pulling power and steady steaming. After nationalisation in 1948, they passed to British Railways and continued working across eastern England. Withdrawn by the mid-1960s, none survived into preservation. Crews valued them for reliability and endurance on long, heavy freight turns.