For heavy service on mountain lines, the Upper-Italian Railway ordered eight-coupled locomotives from Sigl of Wiener Neustadt in 1872 which were similar to the Südbahn class 35. These replaced six-coupled locomotives and became a great success due to their simplicity of construction. They had outside cylinders and outside Stephenson valve gear. On an incline of 1.6 percent, they could haul 450 tonnes at 20 km/h and delivered an output of 620 hp. 

Production was also started at other manufacturers in Italy, Austria, Germany, Belgium and Hungary. In 1885, when 189 had been completed, they were split among the Rete Adriatica and the Rete Mediterranea and called class 420 and 480, respectively. The RM continued to order these locomotives until the total number had reached 293 in 1905. The last batches weighed around 10,000 pounds more than the first ones.

The FS took over the designation of the RA and still called them Gruppo 420. At the time when production was completed, they were already being replaced in heavy service in the mountains by 4-8-0 and 0-10-0 locomotives. Now, they were more and more used in secondary duties on level lines. Many continued to be used for decades, finally as shunters in ports. The last two were withdrawn in Piedmont in 1953.