With the outbreak of the Second World War, the Berlin public transport companies had to stop a large part of the bus traffic to save fuel. Tram traffic has been extended accordingly. The newly established amplifier lines contributed to the distinction of the master lines 200 and 300 numbers. From 1941, the night routes of the bus and the tram networks were later classified into the 400-series numbers. The measures were existed until the end of the war. The last 100 numbers were renumbered on May 31, 1949.