In 1958 the SNCF embarked on a dieselisation program specific to its secondary lines and certain principal lines that were not scheduled for electrification. Assisting this task had been the growth in horsepower from the engine manufacturers. The SNCF were looking at power units in the 1,200hp to 3,000hp category. Specifically three manufacturers products were looked at:
SEMT-Pielstick 16PA producing 2,400hp
From Sulzer the SNCF saw fit to use eighty one 12LVA24's in five separate orders between June 1961 & December 1965, to be installed in the 68001 - 68081 series locomotives. The remarkable styling of these machines was due to the talent of Paul Arzens and the co-operation of four main subcontractors:
Compagnie de Ateliers et Forges de la Loire (CAFL) at St Chamond, with assistance from Fives-Lilles-Cail Company at Givors were responsible for the bodywork and bogies.
During June & July 1963 68001 was recorded under test on the Paris - Cherbourg line, hauling 560 tons as far as Caen, the load reduced to 450 tons between Caen & Cherbourg. Although the line limit was 120 km/h this was exceeded near Serquigny when 130 km/h was achieved. Journey times between Paris & Caen based on these trials would see thirty minutes cut off the schedule.
Deliveries began in the latter half of 1963 with Chalindry receiving the first three. They were quickly utilised on the Paris - Mulhouse route, being entrusted with 850 ton loads. They averaged 11,000km per month with some daily diagrams covering 1,200km. Further lines used by these locomotives included St. Dizier - Chalindrey - Dijon and Nancy - Epinal - Port d'Atelier. Caen received its first machine, 68004 during November 1963, working over the Paris - Caen route. As more locomotives were delivered these covered the Caen - Cherbourg and Paris - Trouville routes. Early into 1965 new deliveries were used on the express Rouen - Mezidion - Le Mans - Tours line and also at Nantes. The arrival of the newer, more powerful CC 72000 series machines saw a transfer of the 68000's between Caen & Rennes.
At the beginning of 1969 re-rating of the power unit was effected with horsepower dropped from 2,650 to 2,400, at the same time the rpm was changed from 1,050 to 1,000, to prolong the life of the power unit and the main generator. From 1970 modifications were made to the power unit's protection devices to limit the number of false shutdowns of the engine and to minimise the occurrence of flashovers.
Between 1977 and the end of 1981 the boilers were removed, replaced by slabs of cast iron to retain an even weight distribution. The driving cabs also received structural modifications to provide better protection for the train crews and by 1985 the number one cab had a second door fitted through the bulkhead to access the engine compartment. The couplers received modifications and simplification to the cabs wrap-round stainless steel styling took place, metalwork replaced by a simple painted white panel. This simplification was also made to a number of the other early SNCF classes.
By 1983 the locomotives originally equipped with an Hispano-Suiza transmission had seen these replaced by equipment from CEM Alsthom. Further enhancements were made to the braking system whilst automatic sanding was fitted.
As the Sulzer power units started to age a large number suffered cracks (in the blocks?) principally to the right of the number six cylinder. These represented some 30% of the repairs to the power units. Initially a type of reinforcement provided a successful repair to this problem. To provide a more long term solution forty engine blocks (?) were ordered from Sulzer, nine to be equipped with thicker plating to avoid the cracking problem. However with the usefulness of this class declining the modifications were suspended in 1993, (this order had been placed with Societe Nouvelle des Ateliers et Chantiers du Havre (ACH), Le Havre,) in the belief that re-engining a dozen of the class with AGO engines taken from retired 68500 series locomotives would prove to be more economic. Changing the interval for the shopping of locomotives at 800,000 km & 1,400,000 km also contributed to better availablity.
Page added March 9th 2002.