The Ferrovie dello Stato Italiane (FS; Italian State Railways) Class 310 (Italian: Gruppo 310), formerly Rete Mediterranea Class 380, was a 0-6-0 steam locomotive; they were the first Italian as-built compound locomotives.
After modifying six of the pre-existing Class 255 to a compound arrangement as an experiment, with positive results, the Ufficio d'Arte di Torino of the Rete Mediterranea designed a two-cylinder compound locomotive meant for mixed service; this design also saw the beginning of the adoption of the Walschaerts valve gear on Italian locomotives.
The round-topped boiler on the first 49 units had standard tubes; however, on the last 20 units it was replaced by one with Serve tubes, which brought the power of these locomotives from the original 430 CV (316 kW; 424 hp) to 500 CV (368 kW; 493 hp).
The Class 310, while an important step in Italian locomotive design, was not a thoroughly successful design; the unique cut-off command for both cylinders made it difficult to equalize the work being done, the starting valve design did not prove entirely successful, and the proportions of the cylinders were also less than optimal. The need to obviate these inconvenients led to the development of the more successful Class 320.
The Class 310 locomotives served on both passenger and freight trains on secondary lines for their whole career; the last units survived till the early 1930s around Asti, but were withdrawn soon after. No locomotive survived into preservation.