The challenges for locomotives on the Gotthard railway were not only the incline of 2.7 percent, but also the spiral tunnels with a radius of 300 meters. This required a high tractive force and at the same time made the adhesion conditions more difficult. In order to be able to dispense with the previously necessary one or two auxiliary locomotives per train, eight-coupled locomotives or those with articulated chassis should be procured. In 1890 Maffei in Munich delivered locomotive number 151 to test the Mallet design.
The tank locomotive had six coupled axles and no carrying axles and was therefore given the type designation Ed 2x3/3. All cylinders acted on the respective third coupled axle. Due to the short distance between the wheels, only the first and last axle of each running gear group could be braked from the outside, otherwise there would have been no space for the brake pads between the wheels. Since enough space had to be planned for the water tanks on the sides of the boiler, the boiler turned out to be relatively small for a locomotive with a service weight of 87 tonnes.
Since a high steaming capacity was required for the long, continuous incline, the Ed 2x3/3 quickly reached its limits. Although the engine offered sufficient traction and was able to convert a lot of power, the boiler was too small in comparison. Calling up full power for a short time was also difficult because the maximum coupler force could be exceeded. Thus the maximum train weight of the Ed 2x3/3 on the Gotthard railway was only 200 tonnes, while the existing D 4/4 could pull 175 tonnes. The Mallet thus remained a one-off while further, reinforced batches of the D 4/4 were purchased.