When the Beira-Bulawayo railway was built in the 1890s, its operator Pauling and Co. ordered six passenger locomotives from the Falcon Engine and Car Works in England. As the line was two-foot gauge, these 4-4-0 locomotives were very small and had a weight with tender of less than 20 tons. The drivers had a diameter of 32 inches and were mounted inside of the frames. The cylinders measured eight by 15 inches. As the construction of the line was subcontracted to Alfred Lawley, these locomotives were nicknamed “Lawleys”, but also “Falcons” after their manufacturer. Their official designation was F2.

Only one year after the delivery of the original six locomotives, production of a heavier variant called F4 was started. These had a larger boiler with a higher pressure, larger cylinders and larger drivers. Visual distinguishing features were the modified design of the louvres on the cab sides and the running boards which made a step in front of the cab due to the larger drivers. By 1898, 26 F2 had been built by Falcon and ten more by Glasgow Railway Engineering led by Dugald Drummond. On the grades of the Beira line, these locomotives could haul 180 tons, compared to 160 tons with the F2.

Due to growing volumes of freight and passengers, the Beira-Bulawayo line had to be converted to Cape gauge in 1900. Initially, most locomotives of the F2 and F4 classes were stored, with only six in use on the Ayshire Railway that still operated on two-foot gauge. Since South African Railways needed to replace locomotives needed for military service in German South West Africa, they bought 13 of the locomotives which were stored in Mozambique. Around 1930, these received the designation NG6 unter which there are better known today. Service with SAR ended in 1935, but some were used by private operators until 1957. Today two can be found in working order on the Sandstone Estates and two are on display at the Vale of Rheidol Museum.