The German term Rekonstruktionslokomotive (abbreviated to: Rekolokomotive or Rekolok) meant 'reconstruction locomotive' and was introduced in 1957 by the Deutsche Reichsbahn in the GDR. The term was used for classes of steam locomotive that underwent considerable rebuilding in order to improve performance, rectify design faults and redress wartime austerity features. At the same time, repairs were carried out. The 'reconstruction' included, as a minimum, the installation of a new high performance steam generation system. Consequently, a characteristic feature of these Rekoloks is a combustion chamber boiler with rectangular mixing chamber (Mischkasten) in front of the chimney.