The 1950 Zeiss Pioneer 1 diesel of 2 cc displacement was surely one of the most original and unusual model engine designs of them all! Nicknamed the "U-Boat" because of its visual similarity to the German military vessel of that name, this fascinating twin ball-race FRV diesel was the first model engine to be produced by the East German branch of the Carl Zeiss Company of Jena, East Germany. The engine is beautifully made and runs very well. It is however both heavy and bulky for its displacement.
The U-Boat represented a bit of a false start in design terms, hence not surviving long in production. The engine is consequently quite rare today. However, the re-designed Zeiss Jena range of model diesels was destined to survive into the late 1960's, with some excellent engines being produced under that trade-name.
Further information regarding this engine and other Zeiss models may be found on Ron Chernich's "Model Engine News" (MEN) web-sit.