The H class was an express passenger steam locomotive

Steam locomotive

A steam locomotive is a railway locomotive that produces its power through a steam engine. These locomotives are fueled by burning some combustible material, usually coal, wood or oil, to produce steam in a boiler, which drives the steam engine...

 that ran on Victorian Railways

Victorian Railways

The Victorian Railways operated railways in the Australian state of Victoria from 1859 to 1983. The first railways in Victoria were private companies, but when these companies failed or defaulted, the Victorian Railways was established to take over their operations...

 from 1941 to 1958. Intended to eliminate the use of double heading A2 class

Victorian Railways A2 class

The A2 class was an express passenger locomotive that ran on Victorian Railways from 1907 to 1963. A highly successful design entirely the work of Victorian Railways' own design office, its long service life was repeatedly extended as economic depression and war delayed the introduction of more...

 locomotives on Overland services on the steeply graded Western line to Adelaide, wartime restrictions led to only one locomotive being built. Nicknamed "Heavy Harry", H 220 was the largest locomotive ever built in Australia

Australia

Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 and the largest non-articulated steam locomotive to run on Australian railways.
By the late 1930s, the aging A2 class 4-6-0

4-6-0

Under the Whyte notation for the classification of steam locomotives, 4-6-0 represents the wheel arrangement of four leading wheels on two axles in a leading truck, six powered and coupled driving wheels on three axles, and no trailing wheels. This wheel arrangement became the second-most popular...

 locomotives, first introduced in 1907, were hauling passenger trains far heavier than those for which their designers had intended them.