The engine numbers on record for the 18 Tonners are a source of some confusion.
They were rostered on the NZASM in the number range from 9 to 14, following on from the NZASM 10 Tonner engine numbers.
The Manning Wardle works records, however, listed them as being numbered in the Delagoa Bay Railway number range from 53 to 58, following on from the engine numbers of the 10 Tonners which also served on the Delagoa Bay Railway.
Furthermore, a Manning Wardle builder's picture of an 18 Tonner shows it with the Delagoa Bay Railway engine number 57.

Similarly, in the works list of the Dutch manufacturer Machinefabriek Breda in respect of the 10 Tonners, those locomotives are also recorded with Delagoa Bay Railway engine numbers 50 to 52 instead of NZASM engine numbers 6 to 8.

It appears, therefore, that the 10 Tonners and 18 Tonners entered service on, or were at least delivered to, the Delagoa Bay Railway and were only rostered on the NZASM at a later stage.

The 10 Tonners and 18 Tonners were all delivered in 1890.
At the time the first ones entered service in March and April 1890, the Randtram line, where the 10 Tonners were to be placed in service, had just been opened, with the first train being hauled by a 14 Tonner locomotive.
However, the construction of the extensions of the Randtram line were still in progress towards the east to Springs and towards the west via Roodepoort to Krugersdorp.
The extension from Germiston to Pretoria was only completed in December 1892, when a start was also made on the line from Pretoria to meet the approaching Delagoa Bay line, but Eerste Fabrieken in Pretoria East was only reached on 13 May 1894.

From the Mozambique end, the bridge across the Komati river was only completed in July 1891, Nelspruit was only reached in June 1892, Waterval Boven two years later in June 1894 and the link-up with Pretoria was only completed at Balmoral in October 1894, more than four years after the 18 Tonners entered service.

Since they were used on construction work, it can therefore be considered most likely that the 18 Tonners were first placed in service on the Delagoa Bay Railway, hence the Delagoa Bay Railway engine numbers, from where they progressed towards Pretoria as the railway was being built.

Whether this could have been the case with all six 18 Tonners as well as the 10 Tonners, or whether at least some of the 18 Tonners were used on construction work from the Pretoria end as well, is not known.
The section from the Delagoa Bay end was completed all the way up to Waterval Boven on the Highveld at about the same time that the section from the Pretoria end reached Eerste Fabrieken in Pretoria East.
The engine numbers on record for the 18 Tonners are a source of some confusion. They were rostered on the NZASM in the number range from 9 to 14, following on from the NZASM 10 Tonner engine numbers. The Manning Wardle works records, however, listed them as being numbered in the Delagoa Bay Railway number range from 53 to 58, following on from the engine numbers of the 10 Tonners which also served on the Delagoa Bay Railway. Furthermore, a Manning Wardle builder's picture of an 18 Tonner shows it with the Delagoa Bay Railway engine number 57.
Similarly, in the works list of the Dutch manufacturer Machinefabriek Breda in respect of the 10 Tonners, those locomotives are also recorded with Delagoa Bay Railway engine numbers 50 to 52 instead of NZASM engine numbers 6 to 8.
It appears, therefore, that the 10 Tonners and 18 Tonners entered service on, or were at least delivered to, the Delagoa Bay Railway and were only rostered on the NZASM at a later stage.
The 10 Tonners and 18 Tonners were all delivered in 1890. At the time the first ones entered service in March and April 1890, the Randtram line, where the 10 Tonners were to be placed in service, had just been opened, with the first train being hauled by a 14 Tonner locomotive. However, the construction of the extensions of the Randtram line were still in progress towards the east to Springs and towards the west via Roodepoort to Krugersdorp. The extension from Germiston to Pretoria was only completed in December 1892, when a start was also made on the line from Pretoria to meet the approaching Delagoa Bay line, but Eerste Fabrieken in Pretoria East was only reached on 13 May 1894.
From the Mozambique end, the bridge across the Komati river was only completed in July 1891, Nelspruit was only reached in June 1892, Waterval Boven two years later in June 1894 and the link-up with Pretoria was only completed at Balmoral in October 1894, more than four years after the 18 Tonners entered service.
Since they were used on construction work, it can therefore be considered most likely that the 18 Tonners were first placed in service on the Delagoa Bay Railway, hence the Delagoa Bay Railway engine numbers, from where they progressed towards Pretoria as the railway was being built.
Whether this could have been the case with all six 18 Tonners as well as the 10 Tonners, or whether at least some of the 18 Tonners were used on construction work from the Pretoria end as well, is not known. The section from the Delagoa Bay end was completed all the way up to Waterval Boven on the Highveld at about the same time that the section from the Pretoria end reached Eerste Fabrieken in Pretoria East.
NZASM 18 Tonner 0-6-0ST