FS Class 746

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{{Infobox locomotive | name = FS Class 746 | bgcolor = 00625A | color = FFFFFF | image = 20110726 FS 746 Milan Museo 6357.jpg | caption = Preserved FS locomotive 746.031 | powertype = Steam

| builder =

Ernesto Breda (50),
Gio. Ansaldo & C. (10)

The FS Class 746 (Italian: Gruppo 746) represents a series of 2-8-2 'Mikado' type steam locomotives operated by the Ferrovie dello Stato Italiane (FS). Although they were the largest steam engines ever produced by FS, they did not hold the record for speed—that distinction belongs to the FS Class 691 series.

Design and construction

The development of the Class 746 was driven by the requirement for a swift locomotive that could match the performance of the '4-6-2 Pacific' FS Class 690 II but with a reduced axle load, thus enabling operation on a broader range of lines. This was accomplished by incorporating an additional driving axle and accepting a lower maximum speed, which involved reverting to an Italian-style leading bogie derived from the Krauss-Helmholtz design. To ensure high efficiency, engineers opted for a symmetrical compound engine based on the Von Borries system, featuring four cylinders—two high-pressure cylinders located inside with their valve motion controlled by the external Walschaerts valve gear. This configuration was atypical in Italy, as compound engines had generally been abandoned following the introduction of superheating technology in the early 20th century.

An initial order for forty units was placed with Ernesto Breda, who completed them in 1922, followed by an additional ten built in 1926. Concurrently, Gio. Ansaldo & C. produced ten locomotives fitted with Caprotti valve gear. These were originally designated as Class 747, but in 1930 they were reclassified under the 746.100–110 subclass designation.

Operations and alterations

Originally, the Class 746 locomotives operated along the primary Milan-Bologna-Florence-Rome-Naples corridor. Following partial electrification of this route, their deployment shifted to the Milan-Turin and Milan-Brescia railways. During the 1960s, these engines were active in Sicily as well as along the Adriatic coast line, with Ancona serving as their home depot, until their phase-out was completed by 1967. Although these locomotives were fast, robust, and capable of hauling both express passenger and freight services, they exhibited challenges when starting and showed instability at or near their maximum speeds—issues attributed to their compound engine design. Additionally, at elevated speeds, the contribution of the low-pressure cylinders to overall power was minimal. Units equipped with Caprotti valve gear also experienced operational difficulties when running in reverse. Due to their rough ride quality and substantial weight relative to typical Italian standards, some crews in Milan nicknamed them "Krassin," referencing the Russian icebreaker famed for rescuing survivors of Umberto Nobile’s polar expedition; this nickname implied that the Class 746 locomotives were prone to damaging the rails.

In 1930, all units underwent modifications to enhance their draughting systems. Two years later, in 1932, four locomotives were converted to feature a simple-expansion engine: two fitted with Walschaerts valve gear (nos. 746.007 and 746.046) and two with Caprotti valve gear (nos. 746.107 and 746.108). These conversions yielded promising results—the modified engines matched the performance of unaltered ones but demonstrated improved efficiency at higher speeds. However, due to extensive electrification progress, further conversions were not pursued.

Accidents and incidents

On February 25, 1956, locomotive no. 746.038 encountered a landslide while hauling an evening express between Ortona and Tollo Canosa stations along the coastal line. Although all passenger cars remained on track, the engine and tender derailed, sinking approximately one meter into the sand with the locomotive’s front dipping into the sea. The recovery operation spanned 31 days and involved constructing a temporary barrier between the sea and the locomotive. After excavating the engine from the sand and elevating it, temporary rails were placed underneath. The main service line was temporarily disconnected and linked to these provisional rails beneath no. 038. Subsequently, two Class 735 locomotives hauled no. 746.038 back onto the main track, after which normal service was restored.

Preservation

Among the Class 746 locomotives, two examples remain preserved today: FS 746.031, which is displayed as a static exhibit at the Museo della Scienza e della Tecnologia "Leonardo da Vinci" in Milan, and FS 746.038, notable for having been swept into the Adriatic Sea near Ortona by a landslide in 1956. The latter was long kept at the FS workshop in Verona and has recently been relocated to Pistoia, where it awaits potential restoration.

Notes

References

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