The 'HH' class letters were adopted in 1956 as part of a class letter rationalisation. This enabled wagons in non revenue service to be easily identified. The HH number group was 1 to 12.
HH 1 - 6 were ex _OO_ wagons 1 - 6. They were assigned to different depots throughout Victoria: North Melbourne, Geelong, Bendigo, Seymour, Ballarat.
HH 7 - 12 were built as _TT_ vans in 1891. By the late 1920's they were placed into breakdown service and assigned to country loco depots: Ararat, Benalla, Dimboola, Traralgon and others.
Depot assignments changed with time depending upon depot importance at the time. When depots closed down, the vans moved to other locations.
The vans contained tools and equipment for rerailing locomotives and vehicles. Detailed lists were supplied for all fittings and tools. This even included specific rope sizes and lengths.
The vans were all removed from service in the late 1980's when road access to the lineside improved and major derailment work was done by road cranes.