The NZASM 46-tonner was a 0-6-4T tank locomotive designed for freight service in Transvaal. It was the successor of the 40-tonner 0-6-2T and had the same cylinder and wheel dimensions. For both the designer and builder was Maschinenfabrik Esslingen, but after only 20 of the preceding design, a total of 175 46-tonners was built between 1893 and 1898. In 1899, Werkspoor built 20 more in South Africa. A prominent feature of these locomotives were the outside frames with visible leaf springs and Hall cranks.
From the last batch built in the same year the Second Boer War started, 16 were directly delivered to the Imperial Military Railways. After the war, they came to the CSAR and became class B, while their 0-6-2T predecessors became class A. They were modernized over time, for example with a modified design of cranks. In this time, 30 were sold to Mozambique which were not needed anymore by the state railway. Others were sold to mines or industry in South Africa.
In service it had been found out that their running characteristics were not very good when running forwards due to the missing leading bogie. So they were often ran backwards. So the SAR, which still designated them class B, mainly used them for shunting at speeds where the running characteristics were good enough in both directions. The SAR withdrew their last ones in 1919, but in Mozambique the CFM used the last ones into the seventies. In mining some operated into the last decades of the 20th century, with some even bought from the CFM. Four have been preserved to this day and No. 230 “Jan Wintervogel” is still being fired up occasionally.