The NZR AA class consisted of ten steam locomotives built by Baldwin Locomotive Works in 1914 to an order by Chief Mechanical Engineer, H. H. Jackson for operation on New Zealand's national rail network.

The United States built locomotives were an urgent order needed due to heavy demand with both New Zealand and British workshops unable to supply as the First World War was draining resources and manpower for the war effort.

Construction was completed less than two months after the order was placed and all ten entered service in New Zealand in June 1915.

[1] They were worked hard for four decades before being supplanted by the more powerful "K" and "J" class families.

They were used extensively on the steeply graded central North Island Main Trunk, Wanganui and Gisborne sections.