The Mathis Vega 42 was a 42-cylinder 6-bank in-line radial piston engine, designed and built in France, by Société Mathis Aviation in the late 1930s, with development continuing during and after WWII.
Émile E. C. Mathis had begun designing and producing motor-cars from 1910.
Société Mathis Aviation, formed in 1937, began designing aircraft engines, initially with the large and complex Vega.
Development continued after the war, culminating in the 119.4 L (7,290 cu in) 3,700 kW (5,000 hp) Vesta 42, which did not reach the hardware stage before Mathis closed its doors.
[1] The Vega engines were run on test-beds, and some sources indicate the engine was flown 100 hours in a test bed aircraft during 1939, but no details of flight testing survive.