In a compound Mallet, the rear set of coupled wheels are driven by the smaller high pressure cylinders, from which spent steam is then fed to the larger low pressure cylinders that drive the front set of coupled wheels.

[4][5] These were successor of the first Mallets the 0-4-4-2T SS Class 500s (DKA BB10s), which were delivered in 1900 and worked on the 3 ft 6 in (1,067 mm) gauge heavy mountain lines of West Java.

They were known as Si Gombar by locals due to the ability on the mountain lines and its huge size.

The Class 1600 proved more powerful than other SS locomotives, and able to haul trains weighing 1,300 tons at a speed of 55 kilometres per hour (34 mph), and being able to negotiate tight curves.

This numbering system remained in use after the Independence of Indonesia by Djawatan Kereta Api (DKA) - the Department of Railways of the Republic of Indonesia until the era of Perusahaan Jawatan Kereta Api (PJKA) or Indonesian Railway Bureau Company.

It was built at the Petone Workshops in Wellington and was designed for use on the world famous Rimutaka Incline.

Numbered 66, making it E 66, it spent the first part of its working life in the Wellington region hauling trains up and down the Rimutaka Incline.

[9] The South African Railways (SAR) operated 57 Mallet locomotives with this wheel arrangement, spread over six classes, all of them 3 ft 6 in (1,067 mm) Cape gauge.

The locomotives were initially used across the Rollins Pass and later on the Moffat Tunnel route of the Denver and Salt Lake.