Because the production of standard locomotives was not envisaged in the first numbering plan and because the upgrade of main lines to 20 tons was proceeding very slowly, the Deutsche Reichsbahn ordered more Class S 3/6 locomotives from Maffei.
In 1927, 12 units of series l were delivered (18 509-520); in 1927/28 they were followed by 8 engines of series m (18 521-528).