The Eb 3/5 was a high-pressure prototype that was built in 1927 at the SLM's own expenses. It was a 2-6-2T tank locomotive with a Winterthur boiler working at 60 bars (870 psi). The firebox had walls and a ceiling made of tubes, with a large drum above. It had a preheater for the combustion air that was removed after a short time since it did not bring the desired effects compared to its maintenance efforts. The cylinders were not mounted in the usual way in front of the driving wheels, but as a three-cylinder uniflow steam motor. It was controlled by a camshaft and transmitted its power through a crank axle.

After completion and trial runs made by SLM it was given to the SBB for use in regular service in comparison with the B 3/4. Here the Eb 3/5 achieved savings of water by 50 percent and of coal by 35 to 40 percent. For short time it could deliver 1,100 kW and its continuous output was 730 kW. In 1930, the firebox heating surface was enlarged from 11.7 to 14.3 m². Although these results were satisfactory, there was little demand for steam locomotives since many lines in Switzerland had already been electrified in the twenties. So the Eb 3/5 remained a one-off and was scrapped in 1940.