The OAA wagon could be seen as a logical progression of the open wagons of yore, they had no explicit purpose in mind upon introduction but to haul a large amount of cargo wherever was required. Introduced in 1971 with a carrying capacity of 31 tonnes the OAA wagons had drop side doors on each side for the easy loading and unloading of cargo.  The OAA wagons saw conversions and rebuilds within a few years of introduction as the railways undertook a move towards specific rolling stock for specific uses, and the need for general wagons became reduced. Many wagons would go on to enter departmental service. A small handful of the wagons are still in service, although these tend to be used as barrier vehicles in the modern era.