The South African Railways Class 7D 4-8-0 of 1915 was a steam locomotive.

Between 1899 and 1903, the Rhodesia Railways placed 52 Cape 7th Class 4-8-0 Mastodon steam locomotives in service. During the Second Boer War, one more was obtained from the Imperial Military Railways in March 1901, as replacement for a locomotive which was damaged beyond local repair capabilities as a result of hostilities during delivery.^[1]

In May 1915, five of these locomotives were sold to the South African Railways, where they were renumbered and reclassified, four of them to Class 7D and the remaining one erroneously to Class 7B. At the same time, the ex Imperial Military Railways locomotive was also sold back to South Africa and was, also erroneously, designated Class 7D.^[1][2][3]

The original Cape 7th Class locomotive had been designed in 1892 by H.M. Beatty, at the time the Cape Government Railways Western System Locomotive Superintendent.^[4]

Between 1899 and 1903, 52 such Cape 7th Class 4-8-0 steam locomotives were built for the Beira and Mashonaland and Rhodesia Railways (BMR), later the Rhodesia Railways (RR). These locomotives were acquired by Southern Rhodesia at the time when railways were still expanding from South Africa via the Bechuanaland Protectorate into Southern Rhodesia in the southwest, and from Beira in Mozambique to Umtali in the east, and while the Second Boer War was in progress. At the time, the system was composed of several smaller railways, still largely under construction, which were eventually all linked up in 1902. These were:^[1]

• The fledgling Bechuanaland Railways (BR), which was still being operated by the Cape Government Railways (CGR), from Vryburg via Mafeking in the Cape Colony to Bulawayo in Southern Rhodesia.
• The Mashonaland Railways (MR), which operated in Southern Rhodesia from Bulawayo to Umtali in the east.
• The Rhodesia Railways Northern Extensions (RRM), which operated north and east of Bulawayo, towards Northern Rhodesia.
• The Beira and Mashonaland and Rhodesia Railways (BMR), which operated between Umtali in Southern Rhodesia and Beira in Mozambique.

The 52 locomotives were ordered in five batches from three British manufacturers.^[1][5][6]

• Twelve were delivered by Neilson, Reid and Company between August and October 1899. They were virtually identical to the SAR Class 7A. Two of them were numbered BR7 and BR8 for the BMR, for service at the Beira end, while the rest were numbered in the range from RR1 to RR10.^[1]

In 1901, eleven of them were renumbered in the range from MR8 to MR18, MR20 and MR21, not in order, for the BMR. The exception was no. RR8, which was delivered damaged beyond local repair abilities, apparently as a result of hostilities, while in transit through the area under control of the British Military near Mafeking. A Neilson, Reid-built 7th Class locomotive of the Imperial Military Railways (IMR), no. IMR 110, was subsequently transferred to the BMR at Umtali in March 1901 as replacement for the damaged no. RR8. It was renumbered to MR19, the number which would have been allocated to no. RR8. The renumberings are tabled below.^[1]

• A second batch of twelve were delivered by Neilson, Reid in August 1900 and numbered in the range from RR11 to RR22. They were placed in service on the line from Vryburg to Bulawayo and shedded at Mafeking. In 1901, four of them, no. RR11, RR12, RR17 and RR20, were relocated to the BMR and renumbered in the range from MR20 to MR23, in order. Many of the Neilson, Reid-built locomotives from both batches were renumbered a second time in 1906, as shown in the table.^[1]
• A third batch of eight locomotives was delivered from Kitson and Company between 1901 and 1903, numbered in the range from RR23 to RR30. These were built with Belpaire fireboxes instead of the usual round-topped fireboxes with which all earlier 7th Class locomotives of the CGR, the IMR and the RR were delivered. They were also placed in service at Mafeking.^[1]
• The fourth batch of ten locomotives, again with Belpaire fireboxes, was delivered from North British Locomotive Company (NBL) in October and November 1903. They were numbered in the range from RR31 to RR40. Of these, numbers RR31 to RR38 were allocated to the Mashonaland Railways-Kalomo-Broken Hill (MR-KB) section. They retained their RR numbers, but had brass plates with the letters "KB" affixed above their number plates on their cab sides, to indicate their ownership. The other two were also placed in service at Mafeking.^[1]
• The fifth and final batch of ten Rhodesian 7th Class locomotives was also built by NBL and delivered in November and December 1903, numbered in the range from RR41 to RR50. They were also placed in service at Mafeking.^[1]

In May 1915, six of the Neilson, Reid-built 7th Class locomotives were purchased by the South African Railways (SAR) to augment its locomotive stock, which was being taxed severely due to war conditions at the time. These six locomotives included the war-damaged no. RR8 which had still not been repaired and consequently never ran a mile in revenue service in Rhodesia, as well as the ex IMR locomotive which had been transferred to Rhodesia as compensation for the damaged no. RR8.^[1][2][3]

These locomotives were initially referred to as Class RR, until they were later designated SAR Class 7D. Five of them were renumbered in the range from 1351 to 1355 on the SAR roster. The sixth, SAR no. 949, was erroneously designated Class 7B.^[1][2][3][7]

During the 1930s, many of the Class 7 family of locomotives were equipped with superheating and piston valves. On the Class 7B and Class 7C, this conversion was sometimes indicated with an "S" suffix to the class letter on the locomotive number plates, but on the rest of the Class 7 family this distinction was not applied consistently. The superheated versions could be identified by the position of the chimney on the smokebox, the chimney having been displaced forward to provide space behind it in the smokebox for the superheater header.^[3][9]

Their builders, works numbers and renumbering are listed in the table.^{[1][2][5][6][10][11]}