Traduction automatique. Texte original en: EN - afficher l'original At the beginning of the 20th century, Switzerland faced a structural railway problem: its most important north–south axis, the Gotthard Line, imposed extreme demands on traction. Long gradients of up to 26‰, tight curves, tunnels and harsh alpine weather made steam traction costly, slow and operationally complex.

During the First World War, coal shortages further exposed Switzerland’s dependence on imported fuel. At the same time, the country possessed abundant hydroelectric resources. These combined factors accelerated the strategic decision of the Swiss Federal Railways to electrify its main lines.

By 1916, SBB had already gained experience with electric traction on secondary lines and lighter locomotives. However, no existing design was capable of reliably hauling very heavy freight trains over the Gotthard route under all conditions. A new type of locomotive was required, designed from the outset for mountain freight service.

Traduction automatique. Texte original en: EN - afficher l'original When the Swiss Federal Railways issued its tender on 30 June 1917, it was not seeking an incremental improvement over existing electric locomotives. The specifications clearly reflected the operational realities of the Gotthard Line and the limitations observed in earlier traction experiments.

One decisive element of the tender was curve negotiability. The Gotthard route imposed tight curve radii that made long rigid-frame locomotives unsuitable. Engineers therefore converged on an articulated design, a concept already proven in steam locomotives but still uncommon in heavy electric traction.

SBB awarded the mechanical construction to Swiss Locomotive and Machine Works (SLM), whose experience with articulated steam locomotives was considered essential. The complete electrical equipment—including traction motors, transformer, control systems and braking equipment—was assigned to Maschinenfabrik Oerlikon (MFO), one of the leading European specialists in AC traction.

The resulting design was not intended as an experimental prototype, but as a standardised production locomotive capable of immediate operational deployment.

Traduction automatique. Texte original en: EN - afficher l'original The Ce 6/8^II was conceived as a carefully balanced compromise between mechanical flexibility and electrical robustness, reflecting the specific operational demands of heavy freight service on alpine routes. Its designers sought to combine high adhesive weight and tractive effort with the ability to negotiate tight curves and uneven track conditions without excessive mechanical stress.

Structurally, the locomotive consisted of three permanently connected sections. At each end were long, narrow driving units, while the central section housed the driver’s cab, the main transformer and auxiliary electrical equipment. These sections were linked by articulated joints, allowing lateral movement between them. This articulation significantly reduced flange wear and track stress on curved alignments while preserving a high proportion of the locomotive’s weight on the driving axles, an essential factor for adhesion on steep gradients.

Each driving unit rested on three coupled driving axles, preceded by a single leading axle that improved guidance and stability. Traction was provided by one large electric motor per driving unit. Power transmission followed principles well established in steam locomotive practice: torque was transferred from the motor to a jackshaft and then distributed to the coupled axles via side rods. Although this arrangement already appeared conservative by contemporary standards, it offered clear advantages in terms of even torque distribution, mechanical durability and ease of maintenance under continuous heavy loads. The choice of this system was therefore deliberate and rooted in operational reliability rather than technological novelty.

Electrically, the Ce 6/8^II was designed for the Swiss standard 15 kV 16⅔ Hz alternating current system. A large oil-cooled transformer, mounted in the central section, supplied power to the traction motors via tap changers. The control equipment was engineered to permit smooth and gradual power application, a crucial feature for preventing wheel slip when starting heavy trains on steep inclines.

Particular attention was paid to downhill operation. The inclusion of electric braking allowed the locomotive to dissipate energy or return it to the overhead line, significantly reducing dependence on mechanical brakes. This capability was indispensable for safe and controlled operation on long descents such as those encountered on the Gotthard Line, where braking performance was as critical as traction.

Between 1919 and 1922, a total of thirty-three locomotives were built and delivered, receiving the numbers Ce 6/8^II 14251 - 14283¹. They entered service progressively as electrified sections of the Gotthard route became available². From the outset, their deployment focused almost exclusively on freight services, where their high tractive effort and robust construction could be fully exploited without the operational constraints imposed by passenger timetables.

From the earliest months of operation, operating crews and maintenance personnel observed that the new locomotives displayed exceptional adhesive performance, stable running characteristics at low and medium speeds and a high degree of mechanical resilience under continuous load. The elongated driving hoods, combined with the visible articulation between the sections, gave the Ce 6/8^II a distinctive appearance unlike that of any other locomotive in service. It was within this professional railway environment that the nickname "Krokodil" emerged, a designation that would soon extend beyond Switzerland and become permanently associated with the class.


¹The first three Gotthard freight locomotives of the Ce 6/8^II type were initially given the numbers 12251 - 12253, but after the delivery of the fourth locomotive they were renumbered to 14251 - 14253.
²Because at the time the first Ce 6/8^II was delivered the Gotthard line had yet been electrified, the new electric locomotive was initially placed into service in Bern. From there, the locomotive could also be used by the SBB on other routes. Shortly afterwards, it was also employed on passenger trains. Only on 29 May 1921 was the entire Gotthard line between Erstfeld and Bellinzona able to be operated by electric trains. Nevertheless, the subsequent new Ce 6/8^II were also commissioned in Bern, as the locomotive crews there had in the meantime become well acquainted with the particular characteristics of the articulated locomotive.

Traduction automatique. Texte original en: EN - afficher l'original With the completion of the electrification of the Gotthard Line in the early 1920s, the Ce 6/8^II entered the phase for which it had been specifically conceived. It rapidly became the principal electric freight locomotive on this strategically vital route, taking over duties that had previously required large numbers of steam locomotives and complex operating procedures. The new electric traction offered a level of consistency and controllability that fundamentally changed daily operations on the alpine line.

In regular service, the Ce 6/8^II demonstrated a strong capacity for sustained heavy haulage on long gradients. Its articulated structure allowed it to negotiate tight curves with reduced mechanical stress, while the distribution of adhesive weight ensured stable running even at low speeds under high drawbar loads. The relatively modest top speed of the locomotive was well suited to the operational realities of Gotthard freight traffic, where reliability and controlled downhill operation were far more important than velocity. The integrated electric braking system proved particularly valuable on long descents, reducing reliance on mechanical brakes and improving overall operational safety.

As the class accumulated operating mileage, it transitioned from a newly introduced design into a fully standardised element of the Swiss Federal Railways fleet. Maintenance routines became increasingly systematic, and operating crews developed a high level of familiarity with the locomotive’s handling characteristics. By the mid-1920s, the Ce 6/8^II was no longer treated as a special-purpose machine but as a routine assignment within freight diagrams, reflecting its successful integration into everyday railway operations.

During the later 1920s and throughout the 1930s, the gradual expansion of electrification across Switzerland led to a broader deployment of the class. While the Gotthard line remained its primary domain, Ce 6/8^II locomotives were increasingly used on other routes requiring high tractive effort, including additional alpine sections and major freight corridors linking industrial regions. This wider use confirmed that the locomotive was not limited to a single line or operating niche but was capable of reliable service across a variety of operating environments.

Traduction automatique. Texte original en: EN - afficher l'original The arrival of newer electric locomotive designs during the 1930s did not immediately diminish the role of the Ce 6/8^II. Instead, it retained a clearly defined position within the fleet as the preferred locomotive for the heaviest freight duties. Its proven mechanical durability and predictable behaviour under load made it a reference point against which newer designs were assessed. By the end of the decade, the Ce 6/8^II had become firmly established not only as a technical success but also as a symbol of Swiss electric railway engineering, its distinctive articulated form and long association with the Gotthard line earning it enduring recognition both within the railway community and beyond.

Traduction automatique. Texte original en: EN - afficher l'original Between 1942 and 1947, 13 Ce 6/8^II locomotives underwent technical modifications that primarily concerned the electrical equipment. Improved traction motors and revised control systems allowed a higher continuous output and permitted an increase in the maximum speed from 65 km/h to 75 km/h. The new traction motors and the lengthening of the bumper beams reduced the weight and the metre load of the locomotives, which meant that they could also be used on branch lines.

Following these changes, the rebuilt locomotives were reclassified as Be 6/8^II in accordance with the Swiss locomotive classification system. In outward appearance, however, the modernized locomotives remained largely unchanged.

Traduction automatique. Texte original en: EN - afficher l'original As the post-war decades progressed, the original Ce 6/8^II locomotives increasingly operated alongside both their modernised Be 6/8^II counterparts and newer generations of Swiss electric locomotives. While the Crocodiles had once represented the highest level of electric freight traction available, developments in locomotive design during the 1950s gradually shifted operational priorities. Newer classes offered higher power, greater speeds and more compact layouts, making them better suited to the growing demands of mainline freight traffic.

Within the Swiss Federal Railways fleet, this evolution led to a progressive reallocation of duties. The non-modernised Ce 6/8II units were increasingly removed from front-line Gotthard service and reassigned to tasks where their limitations were of lesser importance. These included transfer freight movements, local freight services and heavy shunting duties in major marshalling yards. In such roles, their strong tractive effort at low speeds and their well-understood mechanical behaviour continued to be valuable assets.

Despite their advancing age, the Ce 6/8^II locomotives remained operationally reliable. Their conservative mechanical design, derived in part from established steam-era practices, proved resilient under prolonged use.

Traduction automatique. Texte original en: EN - afficher l'original The first of the original Ce 6/8^II to be retired was from 1965 on.

At the same time 11 units began to be converted for use at large switch yards, whereby the following changes were done: installation of switching radio, removal of one pantograph, and installation of new platform railings in front of the hoods.

Traduction automatique. Texte original en: EN - afficher l'original By the late 1970s and early 1980s, the remaining Ce 6/8^II locomotives were confined almost exclusively to secondary duties. Their role within the network had become marginal, yet their continued presence illustrated the exceptional longevity of the design. The final withdrawals took place in 1986, marking the end of regular service for the original Ce 6/8^II configuration nearly seventy years after the class had first been conceived.

Following their withdrawal, the historical significance of the Ce 6/8^II was widely recognised. Seven locomotives were preserved by museums and railway heritage organisations, while others were retained as monuments or for static display.

Today, the Ce 6/8^II stands as a foundational chapter in the history of Swiss electric traction, embodying both the early ambitions of railway electrification and the durability of a design shaped by the demanding conditions of alpine freight operation.