When I ran into this mammoth radial I thought it had some aviation use. I did not find any connections but decided to show it anyway as it is one of the largest radial engines ever built.
The Zvezda M503 was a 6 row, 42 cylinder diesel radial engine built in the 1970s by the Soviet Union. Its primary use was in Soviet missile boats, which used three of these engines.
This engine may have had other applications, but due to its extreme weight (12,000 lb (5,400 kg)), it would have been limited to ground or naval applications.
A German tractor pulling team designed a vehicle around a methanol-fueled version of this engine, this modified engine is said to weigh 3,200 kg (7,100 lb) including the gearbox, for use in the 5.4 ton tractor pulling class, making 8,000 hp (6,000 kW) at 2,500 rpm.