Opposed piston engines do not all have two crankshafts per cylinder. Some have had one crankshaft below vertical cylinders with the top pistons driving the crank via long paired connecting rods (in tension for the power stroke). Doxford marine engines for example.
Opposed piston engines have two world firsts to their credit. In 1903 Louis Rigolly took a 13.5 litre Gobron Brillie on to the sands at Oostende and was timed at 103 mph making the GB the first car to exceed 100mph. Its engine was of the single crankshaft type described . In 1971 Mitsubishi built "Ocean Prospector" the world's first self-propelled semi-submersible drilling rig. It was powered by four ex-US submarine Fairbanks Morse engines, which had two crankshafts geared together. These engines supplied all the rig power. For rig moves propulsion came from two ex-US submarine electric motors driving propellers in steerable Kort nozzles. In calm water these engines could drive the 12,000 ton rig at 6 knots although in practice it was always towed as well. This rig has recently been brought out of layup and is being prepared to go to work again after 50 years. I think it unlikely to have the same engines though.
A final opposed piston configuration was employed by Rootes for a truck engine. This had three horizontal cylinders with a central crankshaft beneath them. Force from the pistons was transmitted through big rockers at each end. The core engine ignoring accessory drives thus had 3 cylinders, 6 pistons, 6 rockers, 12 connecting rods, 1 crankshaft and 34 bearings. It went into service and reputedly performed well. One peculiarity was that at high power e.g. when climbing hills in low gear it emitted a banshee wail. Its drivers called it "the Commer Screamer".
