It was unique in Germany at the time for featuring thyristor chopper control and a contemporary design by Prof. Herbert Lindinger.
Electron tube types of DC motor controls began to be developed in the 1920s but electronic controls didn’t seriously begin to displace the Ward Leonard system until thyristor controlled drives were developed in the late 1960s.
As thyristor technology advanced rapidly, SNCF decided to adopt the new technology for a new series of locomotives, later known as the "Nez Cassés (Broken Noses, due to their cab styling by Paul Arzens)" or "BB 4400kW".
A thyristor drive is a motor drive circuit where AC supply current is regulated by a thyristor phase control to provide variable voltage to a DC motor.