The prototype, EF63 1, was produced in 1962 by Toshiba for testing before full production of the class started in 1963 spread between manufacturers Kawasaki, Mitsubishi and Toshiba. The class was equipped with a number of special safety features to cope with the unique conditions of operating on the 66.7‰, 6.67 % gradient of the Usui Pass. These included independent dynamic brakes on all six axles (hence the large louvres along the bodysides for heat dissipation), magnetic adhesion brakes operating directly on the rails, and mechanical locking brakes. Small wheels attached to the centre bogie were used to measure the train speed and apply the brakes in the case of run-away. The class used the same 425 kW MT52 traction motors used on the EF62s and also the EF70s.
