The prototype NN1 entered service in 1901. A further forty five wagons were built in 1907. They were numbered 2 - 46 and built to a slightly different design.
Five of this class were scrapped in 1924. This was the start of a project to convert all wagons in the class to _O__ hopper wagons. The traffic was coal from Yallourn to Newport Power Station. The project was abandoned for reasons unknown. The wagons scrapped were numbers 17, 28, 36, 39 and 46. The hoppers were used to make O 1 - 5.
During 1950/51, one hundred welded NN hopper wagons were built to a new design. These wagons were numbered 46 - 145.
Between 1960 and 1967 the capacity of the vehicles was raised. This was achieved by welding up the hopper side access doors and raising the sides by about 30cm. On the 46 - 145 number group, end supports were added for load bearing support. NN 139 had the sides raised but no end supports fitted.
In the 1979 recoding the class was recoded to VHWA.