During its five-year existence, the Swiss National Railway procured a total of 18 tank locomotives of three different types, all of which were supplied by the Swiss Locomotive and Machine Works in Winterthur. A total of twelve of them formed class A, which was intended for passenger and express trains. They are better known under the designation Eb 3/4, which they later received according to the Swiss scheme.

In Switzerland they were the first tank locomotives of the Mogul type, i.e. with one leading and three coupled axles. Since the railway department had doubts about the running characteristics of such a machine with a leading axle mounted in a drawbar in the conventional way, the SLM had to design the leading axle as a radially adjustable Adams axle. Thanks to the cylinders arranged behind the leading axle, the running characteristics would probably have been sufficient in practice even with a cheaper bissel axle. The water supply was carried in the box-shaped frame.

The locos largely resembled the four series B freight locos, which were later designated Ed 3/4. The differences concerned a driving wheel diameter of 1,600 instead of 1,300 mm and the number of heating pipes. After the bankruptcy of the SNB in 1880, the locomotives came to the Northeast Railway. A Klose spring brake was installed there as a continuous brake, which was soon replaced by an air brake. The decommissioning took place between 1896 and 1901.