The R12 was powered by a single BMW M56S6/212 petrol engine capable of providing 18 hp strength at 3,400 revs per minute and 20 hp strength at 4,000 revs per minute if the engine featured a twin carburator, and was capable of propelling the R12 at 110 km/h and 120 km/h respectively. The R12 had an option of either a single or twin carburator engine, both using a battery ignition system, or an Einvergasermotor with magneto ignition. The R12 had claw-switched four speed forward gearbox, with the drive shaft on the right-hand side of the vehicle near the rear wheel. The front and back tires were interchangeable, and Caradan joints were used on the R12 before being replaced by standard drum brakes. The R12 measured 2.10 meters long, 90 centimeters wide and 94 centimeters high, and weighed approximately 162 kilograms without crew, passengers, or cargo load. The R12 required a crew of only one driver, and could carry a single passenger on a seat behind the driver, or, in place of the passenger, up to 745 cubic centimeters of cargo could carried, and the fuel tank had a fourteen-liter capacity.
The R12 was first introduced for civilian use in 1935, along with the BMW R17, at the German Automobile Exhibition in Berlin. The Wehrmacht, during its rearmament, required a suitable military motorcycle for reconnaissance and staff duties. The R12 then entered military service, and was extensively used, some 36,000 models in total being manufactured by 1942. For military purposes, the R12 was manufactured with the Einvergasermotor. In 1942, BMW ceased to produce the R12 in favor of the newer military motorcycle, the R75.