With progressive electrification at the SBB, on the basis of tests with the Fb 2/5 the Buchli drive was selected as the preferred drive for express locomotives in the lowlands. The Ae 3/6I now had the asymmetrical wheel arrangement 2-C-1, since the bogie had to carry the transformer. It could initially be approved for 90 km/h and later for 100 km/h. The last 78 locomotives built after 1925 were designed for use with lightweight express trains at speeds of 110 km/h. With the delivery of the Re 4/4I, they were increasingly used with passenger and freight trains. In the end, they were mainly used with regional trains until the last ones were finally retired in 1994. 