Introduction It was evident in 1950 that additional motive power was required in the North Island, but dieselisation had not yet begun. Consequently, NZR decided to order new locomotives from NBL to the design of the successful J class of 1939. In January 1951, the order was placed for 16 JA class locomotives as coal burners, which made NBL regard it as essentially a repeat order for the J class. In April of the same year, the NZR Chief Mechanical Engineer requested the order be changed to oil-burning due to the perceived long-term coal shortage caused by the
1951 New Zealand waterfront dispute. The associated strike by miners, unavailability of shipping for coal, the expected long-term high imported coal price, and the long time it would take to build up coal stocks to safe levels were the main reasons for the change. The locomotives were eventually completed with oil burning equipment, with no grate, ash pan, or fire door, making them the only locomotives on the NZR to be built entirely as oil burners. These engines had several differences from both the J class and the Hillside JA class. They were manufactured with the cross-compound pump and had roller bearings limited at the connection between the driving and connecting rods, while mechanical lubrication was employed. ACFL blowdown was incorporated late in their construction. A significant improvement was made with the incorporation of French TIA, blowdown equipment which enabled rapid ejection of boiler sludge, reduced boiler scale, and enabled much faster turnaround and higher availability. The system of injection of the oil flow into the burners was different and far more effective than in 1948–1950 conversion of 12 J class locomotives to oil burning. Other detail differences were the use of Stone's headlights and electrical generator instead of the usual Pyle National equipment, the "Butterfly" number boards on the front headlight, and the absence of a smokebox number plate (although a smokebox plate was specified by the NZR).
In service The North British JA class were constrained to the North Island and were mostly used on routes that were commonly worked by oil-burning locomotives. Described by the author Stewart as "fine clean-lined machines", they handled almost every express train in that region for about twelve years. The first eleven locomotives, JA 1275–1285, were based in Auckland, while the other five, JA 1286–1290, were initially based at Palmerston North before being moved to Napier in 1963. The Auckland-based locomotives were regarded as specialised express engines and were more impressive performers than the
KA class locomotives by most Auckland engine drivers. They were regularly assigned to the
North Auckland Line (NAL), the
Opua Express until 1959, the Helensville local until 1966, and the
North Island Main Trunk (NIMT) services, such as the Auckland–Wellington, 227/626 Express Mail train, and faster Night Limited, and Auckland–Wellington express goods train 627. There are accounts of them being used elsewhere. For instance, there are surviving accounts of JA 1279 running on the
Waiuku Branch in the early 1960s, and later on the
Raetihi Branch during the same decade after coal-fired
AB 700 caused several lineside fires. When working with other 4-8-2s on the NAL, they were required to have a bogie wagon such as a UB flat wagon between them to distribute weight more evenly on the light bridges along that line. By contrast, the five Palmerston North-based engines were less frequently assigned to the NIMT trains. Instead, they ran over the
Marton - New Plymouth Line to Wanganui and the
Palmerston North - Gisborne Line as far as Gisborne. By comparison, the Palmerston North-based JA class spent more time working freight trains, particularly with the arrival of the 88-seater railcars. The rest of the steam fleet, excluding the J and JB classes, experienced increased mechanical failures and repair costs while moving the heavier post-war traffic on the NIMT. By 1955, the
K and
X classes of 4-8-2 locomotives were worn out. The 9 K class was rebuilt with KA frames in 1955–57 since it was unacceptable to write off the K class locomotives and retain useful
Baldwin AA. The superiority of the
DA class diesels and JA class meant that an A-grade overhaul for a K class member in 1961 turned out to be the last such work for that class. An analysis done in 1959 found that the North British JA matched the availability of the new DA class, with each JA available for 252 days a year on the North Island. The cost per mile for the JA was much higher, with the locomotives achieving 82% of the DA class' mileage. After the start of dieselisation in the 1960s, the locomotives were transferred to Frankton Junction. Although JA 1286 was briefly transferred to Auckland in the mid-1960s, it was felt that it did not perform as well as the eleven Auckland-based locomotives and was quickly reallocated to Frankton. After this, the locomotives were mostly assigned to the old
East Coast Main Trunk Railway between Hamilton, Tauranga, and Taneatua, again largely on freight trains due to the reduction of passenger services from Taneatua to Te Puke, which was by then handled by the 88-seater railcars.
Withdrawal and disposal Although being a relatively young class, some of the North British JA members were among the first of the J types to be withdrawn. In 1964, JA 1279 was the first of the class to be withdrawn and sent to
Hillside Workshops without at least one driving wheelset, which was taken to repair JA 1275 after it suffered an axle fracture while passing through Mercer that year. The rest of the locomotive became a source of spare parts for the J and Hillside JA class locomotives in the South Island. The oil-fired boiler was converted to coal-firing before being fitted to Greymouth-based J 1212 during a C-grade overhaul. As the locomotives were withdrawn, most of them were stripped of parts to keep the South Island J and Hillside JA class locomotives running, along with the remaining North British JA class which, by then, were based out of Frankton Junction. In November 1966, tenders from JA 1287, 1288, and 1290, which were in relatively good condition, were transferred south. They were rebuilt to accommodate a coal bunker in place of the fuel oil tank and coupled to J-class locomotives whose original 1939-built tenders were life-expired. Other surplus North Island JA parts were also refitted, including the trailing trucks, and approval was given to fit the JA 1288's boiler. Most of the North Island JA was withdrawn too late in 1967 or early 1968 to be reprocessed, as A-grade South Island J overhauls had ceased with dieselisation. JA 1281's boiler was refitted to J 1236 in an A-grade Hillside overhaul in 1967, with the firebox converted from oil to coal burning, but with all the oil firing fittings left in place, making it easier for restoration and reconversion to oil burning in 1991-2001 for rail excursions. The boiler of JA 1278 was withdrawn in March 1968 and installed that year in a C-grade overhaul of JA 1252 in Dunedin. Only four of the North British JA class managed to reach the end of North Island steam in 1968, JA 1275 being one of them. After the withdrawal and removal of all useful parts, the North British JA class were sold to Sims Pacific Metal Industries and towed to Sims Otahuhu scrapyard, adjacent to the Otahuhu Workshops, for scrapping. JA 1275 was the only locomotive to avoid this fate. ==Preservation==