The incline at Rovniebera was always a severe test for the RSR's locomotives, goods trains often being hard put to surmount the 1 in 45 gradient and making the need for an effective banking locomotive more and more urgent. The trials and tribulations of the class CB1 Hagans 4-6+4-2T of 1904 made Karel Belčamin very wary of articulated locomotives and the RSR had to press various underpowered or otherwise unsuitable engines into service. Indeed, only the solitary class D7 4-8-2T, which was rebuilt from the CB1, was able to provide really useful assistance. In 1909, however, Beyer Peacock of Manchester delivered the first Garratt locomotives to Tasmania and in just a few years the type had gained acceptance in many parts of the world. For Belčamin, the Garratt was heaven-sent and he wasted no time in drawing up the design we see here. The engine units were standard with the class D8 0-8-0 of 1910, albeit with 2-cylinder compound drive at each end. Weight in working order with tanks and bunker 3/4 full was estimated at 103 tonnes and permitted in theory a tractive effort of over 60,000 lbs. An engine of such power would have had no difficulty in hauling the RSR's goods trains up Rovniebera Bank unaided, let alone just banking them, but the ride at normal working speeds (going down the other side, as it were) would have been anything but smooth.

After consultations and not a little haggling with Beyer Peacock, the RSR board came to the conclusion, much to the chagrin of both Beyer Peacock and Karel Belčamin himself, that despite its great power, the DD1 would have represented too large an investment in a locomotive of limited applicability, bearing in mind also that with only a few units being ordered the price would have been very high.