Dornier Do 335 Pfeil
The Dornier Do 335 Pfeil was a German heavy fighter of the Second World War built around two engines mounted in line in one fuselage, the front one pulling and the rear one pushing. The layout made it one of the fastest piston-engined aircraft ever flown, but it arrived too late and in too small numbers to see combat, and only one example survives, in the Smithsonian's collection.