[1] When the FS were created in 1905, Chief Mechanical Engineer Giuseppe Zara undertook a process to design a standard range of locomotives; one of these was the Class 630, a light express engine which, together with the other designs, shared the features of being compound locomotives.

However, with the diffusion in Germany (then in close ties with Italy because of the Triple Alliance) of the Schmidt superheater, a decision to build there a batch of 24 non-compound and superheated versions of the Class 630 (keeping all the other features, including the Italian bogie and the peculiar inside-cylinders/outside valve chests and valve gear) was taken.

[2] Results were highly successful, and subsequently almost all steam locomotives in Italy would be built with simple expansion and superheating.

The first locomotives were built by the German firm Schwartzkopff (as the Italian industry lacked experience with the superheating technology), with other Italian firms building the rest, for a total of 169; four more Class 640 were added in 1951 when the railway company for which they had been built for (Strade Ferrate di Biella) was incorporated in the FS.

[1] Between 1929 and 1931, fifteen Class 630 locomotives were rebuilt with superheaters, simple expansion and Caprotti valve gears.