DKW RT 125

In the 1930s DKW pioneered the Schnürle two-stroke loop scavenging process to dispense with the use of a deflector piston and improve efficiency of the combustion chamber.

Competitor companies such as Adler and TWN copied the adoption of flat-topped pistons and strove to develop equally efficient transfer port arrangements without infringing DKW's patent.

WFM of Poland made a modified version of the RT 125 (under SHL 125 and Sokół 125 brands), developed into 125/175 cc family motorcycles, produced until 1985.

Since the copyright on the RT 125 had been voided by the Allies, the company reverse engineered it as the basis for their first motorcycle.

The YA-1 inherited design characteristics of RT 125 and, due to its thin body and chestnut brown tank, was affectionately nicknamed the Aka-tombo (赤トンボ, "Red Dragonfly").