In 1898, the Queensland Railways received two rack locomotives from Dübs. They were numbered 339 and 340 and were used on the line that led to the gold mines at Mount Morgan in the Dawson Valley. This had a section with an incline of 1 in 16 or 6.25 percent over nearly one and a half miles that had been equipped with an Abt rack rail. The locomotives had a 0-4-2RT wheel arrangement, four cylinders and a Le Chatelier counter pressure brake.

The class designation 4D11½ stood for four driving wheels, tank locomotive and a cylinder diameter of 11½ inches. The boiler pressure was originally 175 psi, but was reduced to 150 psi to prevent slipping on the adhesion sections. Together with a B13 or B15 locomotive they could haul 80 tons up or down the 1 in 16 incline. They were pushed back into the second row already in 1900 when the more powerful 6D13½ Abt class was introduced. Their withdrawal years were 1916 and 1922.