The story
The inception of the company resulted from the merger of two companies, Grondona Comi & C and Miani Silvestri & C in 1899. Originally, OM manufactured railway stock. Car production started in 1918, using the plant of the former Brixia-Zust (Brixia-Züst), just after OM took over Zust car company of Brescia, Northern Italy. The first OM car, the Tipo S305, was derived from an old Zust model. It appeared in 1918, fitted with a 4,712-cubic-centimetre (287.5 cu in) inline four-cylinder, side-valve engine.
From Wikipedia’s article on Officine Meccaniche, shared under CC BY-SA 4.0.4