With traffic increasing over the steeply-graded Gotthardbahn through the late 1960s and early 1970s, methods of shifting heavier loads were sought. The Ae6/6 locos, constructed in stages between 1952 and 1966, were making a good account of themselves on this work, but with their six powered axles spread over only two bogies, the forces exerted on the locos when traversing curves were considered of concern – and the Gotthardbahn is very serpentine in nature.
The result was experimenting with Bo-Bo-Bo high-power, high tractive effort electric motive power – retaining the six powered axles but now spread over three bogies. Four 10,700hp prototypes – 11601 to 11604 – entered traffic with the SBB between September and December 1972 and were immediately put to work on intensive testing across Switzerland. Reflecting their higher plated speed, these were known as Re6/6.
11601 and 11602 differed from the other two – taking their cue from the RhB Ge6/6 II locos – in having a split bodyshell allowing vertical movement halfway down the loco. This was quickly deemed inferior to the solid loco box of 11603 and 11604 as they provided quite an uncomfortable ride at speed.
85 production machines were eventually ordered based on the latter two prototypes, logically numbered 11605 to 11689. These entered service between 1975 and 1980; 11613 notably being the 5000th locomotive to be produced by SLM at Winterthur (see photo here). They very quickly became the standard serious heavy freight traction across Switzerland, not just on the Gotthardbahn but also elsewhere, such as on the oil traffic through the Rhône valley. They were also used on passenger trains, but were never equipped for push-pull operation, on account of their immense power being deemed far too excessive to safely push a train!
Very early on in the class’s life, a serious fatal accident befell 11640 inside the Simplon Tunnel on 23rd July 1976. The locomotive was, however, repaired with a newly fabricated bodyshell, and re-entered traffic with a new works number in 1978.
The first of the 89 machines to be written off, however, was 11638, following an accident at Saxon on 16th February 1990. It too was hauling a passenger train that had come through the Simplon Tunnel, and was running at design speed when it hit an item of on-track plant (XTm 91571) that it appears had been forgotten about following track works. The impact was severe and the loco was all but destroyed; it is amazing that only three people died. The SBB apparently did consider rebuilding the loco, as with 11640 – Re6/6s being a precious commodity – but with Re460s already in the pipeline, this was not pursued.
Since 2003, all of the Re6/6s have been dedicated to freight traffic, but very occasional railtour appearances do occur. This, currently, is your only real chance to ride behind this impressive class these days; the last service train working that I am aware of was 620 088 (ex-11688) in charge of EN 464, the Graz to Zürich overnight, from Feldkirch on the early morning of 9th March 2018 (photo here) as a pre-arranged – but secret! – “fix” in connection with a driver’s retirement.
As intimated above, the locos have been renumbered into the 620 0xx series over recent years, but even approaching the half-century for the oldest machines, most of the fleet remain in traffic and are largely still in use on the duties for which they were designed. They cannot work outside Switzerland, although 11632 was temporarily fitted with an Austrian pantograph that allowed it to conduct some tests around Linz in September 1993.
Two of the prototype machines – 11603 and 11604 – were sold to RailAdventure in August 2018, have been repainted into their grey house colours and are now seeing use on their new owner’s core duties of stock transfer and testing work.
It is to be hoped that the sight of these very powerful and very successful locomotives can be enjoyed on the Swiss main lines for many years still to come. This has seemed assured since 2016 when an SBB Cargo programme to refurbish 25 of the class, at a cost of 1.58 million CHF per loco, to extend their operational lives until 2035 was announced (see link here).
Hopefully, also, some examples will pass into preservation when their number is finally called.