As the designation suggests, the A 3/5 was a type of express locomotive with five axles in total, of which three were powered. It was ordered after the 4-4-0 of the type A 2/4 had become too weak for heavier and heavier express trains. So it became a 4-6-0, since the third driving axle allowed for a higher adhesive weight and a bigger boiler. In place of the old two-cylinder cross compound, the new locomotive was a four-cylinder De Glehn compound. Its basis was the A 3/5 series 201 to 230 of the Gotthard Railway, but the drivers were enlarged from 1,610 to 1,780 mm for higher speeds and the firebox had been made larger.
Typically for the De Glehn design, the two high-pressure cylinders were mounted on the outside behind the bogie, while the two low-pressure cylinders could be found on the inside below the smokebox. Only the first two, numbered 701 and 702, were delivered to the JS before it became part of the SBB. The state railway ordered 107 more of this design, which were numbered 703 to 809. The wheelbase of these had been increased by 250 mm to accomodate a longer firebox.
In parallel to the saturated four-cylinder De Glehn compound, two prototypes each were built from three modified designs. Numbers 501 and 502 were saturated three-cylinder simples, where all three cylinders were mounted below the smokebox and drove the first set of drivers. 601 and 602 were superheated four-cylinder Von Borries compounds with the large low-pressure cylinders on the outside. 651 and 652 were saturated four-cylinder De Glehn compounds like the basic variant, but had a Brotan boiler.
By 1909, a total of 115 were built, including the six prototypes. For further orders, the SBB chose the 601 and 602 prototypes and got 47 more between 1910 and 1915, numbered 603 to 649. These could be distinguished from the original locomotives by the arrangement of the high and low-pressure cylinders. From the series 701 to 809, 68 were superheated between 1913 and 1923. 22 got a 21-element superheater with 37.6 m² of surface and the other 46 got one with 24 elements and 46.2 m². Most were already withdrawn in the late twenties or early thirties due to the electrification of more and more lines, but some saw service into the fifties. Only 705 was preserved by SBB Historic and is still in working condition.