During the development of the standard electric locomotives, it quickly became clear that in the future the fast four-axle E 10 and the heavy six-axle E 50 would not be sufficient to serve all train types adequately. The E 40, which was primarily intended for freight trains, thus was developed from the E 10 by reducing the gear ratio and eliminating the dynamic brake. With a maximum speed of 100 and later 110 km/h, it could haul trains of 2,100 tonnes at 90 km/h on the flat and was still fast enough to be able to haul passenger trains if necessary.
The last series, also known as class 1408, was equipped for push-pull operation and multiple working. This meant that push-pull trains could be run in S-Bahn-like operations on the one hand and heavy freight trains on the other. Some locomotives even had knuckle couplings for hauling heavy ore trains. Another modification was the E 4011, better known under its later class designation 139. The 31 examples were intended for use on steep stretches and were again fitted with an dynamic brake.
Including the class 139 879 examples were built, making them the most numerous standard electric locomotive. Over time, their use in front of passenger trains disappeared from their everyday field of activity, but they remained indispensable in use in front of freight trains for a long time. Only after the turn of the millennium did the stock at DB AG fall to around 300 units due to the introduction of new three-phase locomotives. Later, depending on the development of the economy, the remaining ones were stored and reactivated several times as required, e.g. to compensate for missing capacities or to replace failed locomotives. The last of these were retired in 2014, but there are still many examples with private railways.