19 - 1801 diesel locomotive. Dieselisation

This locomotive features an aerodynamic design, highly characteristic of American locomotives. It was manufactured by the ALCO company in the late 1950s. It was mainly used on Galician routes, where almost all the entire network was unelectrified. The initial depot of this series was in Monforte de Lemos; it was responsible for pulling the main express and freight trains between Ponferrada, Monforte de Lemos, A Coruña, Vigo, Ourense and Santiago de Compostela. They were in service until 1994.

Diesel power was the last type introduced into the railway. In Spain, its generalised use did not come about until the mid-20th century. Unlike the electric system, it does not require expensive installations and is therefore more flexible, since it can be operated in all types of lines. However, diesel engines are more polluting, nosier and dirtier than electric ones and have less features, which is why they are currently used for secondary traffic in unelectrified lines and for carrying out manoeuvres. Even so, their energy efficiency is far superior than steam, which they gradually replaced in unelectrified lines.

While mostly European material was used in the case of steam and electric power, it was North American technology that was introduced in the case of diesel, since it was developed the most in the United States. Even today, diesel trains are still the most numerous ones in that country.