The dual-power Eem 6/6 were designed for heavy shunting in large yards or stations, where not all tracks are electrified, but most of the shunting can be done electrically. In 1970-71, SLM and Sécheron delivered the six Eem 6/6 17001 to 17006 shunting locomotives for the Basel and Chiasso marshalling yards.
In terms of construction, they were two short-coupled Em 3/3 and Ee 3/3 IV. The half section with the driver's cab contained the electrical equipment. The twelve-cylinder SLM diesel engine, the generator and the cooler were located in the other locomotive part.
Since this was a small locomotive series, components of other locomotive types were used as far as possible. The drive of both locomotive halves (trucks, wheel sets, coupling rods) were the same as the Ee 3/3 IV, as well as the traction motors including gearboxes and the SAAS mercury vapor rectifier with grid control. The diesel equipment including the generator corresponds to that of a Bm 4/4. The total weight was quite heavy, 104 metric tonnes. Their power was 800KW / 1045 hp in electric mode and 400 KW / 533 hp in diesel mode.
Thanks to the fine level of control, these engines were particularly suitable for use in hump service in both electric and diesel mode. But they were not very successful. They were converted to diesel-only engines Em 6/6 17001 - 17006 between 1984 and 1993 and discarded between 2003 and 2005. When converting to a pure diesel locomotive, the transformer was replaced by ballast in order to maintain the balance of the locomotive.