the Indian WAG-12. B′B′ The B′B′ or B-B arrangement is similar, but usually applies to diesel-hydraulic locomotives rather than diesel-electrics. The axles on each bogie are coupled together mechanically, rather than being driven by individual traction motors. Diesel-hydraulics have their engine mounted on the main frame of the locomotive, together with a hydraulic transmission. Power is then transmitted to the bogies by cardan shafts and a short driveshaft between axles. A common example of this is the German V200 design and its many international derivatives. The need to arrange the bogie suspension around the drive shafts led to an unusual bogie design with radius arms rather than hornblocks and so prominently visible wheels and rims. In some rare examples, such as the SNCF Class BB 71000 and the narrow-gauge , the bogie axles have been linked by coupling rods. Having only a single final-drive per bogie allows more room for the bogie pivots on this narrow-gauge design. With high power full-size locomotives, splitting the drive directly to two axles is preferred, as it only requires a less powerful final drive gearbox. In AAR notation a Bo-Bo is regarded as a B-B because the AAR system does not take traction motors into consideration, only powered axles. An AAR-like notation is used in France too, making it hard to tell the B-B and Bo-Bo engines apart, both of which are common there. 1A-A1 (or A1-1A) Railcars and multiple units use similar two-axle powered bogies and many of them use similar hydraulic or mechanical transmissions, rather than traction motors. However railcars are also lightweight and do not require all axles to be powered in order to gain adequate adhesion. They thus use a wheel arrangement of 1A-A1 (UIC: (1A)(A1) ) (or A1-1A (UIC: (A1)(1A) ) ) rather than B-B. A common arrangement is for each power car to have two independent engines and transmissions, each driving a single axle of each bogie. The difference between 1A-A1 and A1-1A is that 1A-A1 has the powered axles closest to the middle of the car, whilst A1-1A has the powered axles closest to the ends. 2-B The 2'Bo' (AAR:2-B) arrangement has been used similarly, but rarely, for lightweight railcars that only needed two powered axles. Only one example is recorded, the diesel-electric four-car Rebel railcars of 1935. Three powercars were built, with a 600 bhp engine and two traction motors on a single bogie. Half of