At the beginning of the 1970s FS, during a plan aimed at the expansion and modernization of current service, designed a new version of an unified diesel locomotive which could also resolve the issue of supplying power to heat carriages in an efficient way through a high voltage 2,800 V[2] head end power supply (REC) fed by a secondary generator.

Previous diesel locomotives were not provided with this and so required the use of a generator wagon (Carro Riscaldo), leading to increased weight.

The first series of locomotives, introduced from 1974, were built with curved front windscreens which would be later replaced by cheaper and sturdier flat ones.

A high tension secondary DC generator provides a 300 kW (400 hp)/2750 V output, able to supply enough power for 7/10 coaches depending on the type of climatising equipment installed.

The prime mover is a FIAT A210-12 supercharged engine with 12 90° “V” cylinders with a displacement of 95.7 L (5,840 cu in) that produces 1,560 kW (2,090 hp) at 1500 rpm.