The class J locomotives were subsequently reassigned to haul local freight trains; all but one were retired and scrapped by the end of October 1959.

[3][4] The N&W mechanical department team originally considered a class N 4-8-4 type, but deemed its 63 in (1,600 mm) driving wheels inadequate for the N&W's railway grades.

[3][6] In late 1940, N&W passenger car supervisor Franklin C. Noel originally drew a design, which was based on the Southern Pacific GS class, but the N&W officials rejected it to be "too plain".

[7][8] On the third and final concept, Noel developed the class J bullet-nosed design to give the locomotive smoothness and beauty along with speed, power, and dependability.

[3][7] His wife Louise suggested painting the locomotive black with a Tuscan red stripe wrapped with golden yellow linings and letterings.

[11] It sported a streamlined pilot with a retractable coupler that could horizontally swing out, a bullet-shaped nose with an enclosed headlight mounted into the nose, and a skyline casing that encased the smokestack, sand dome, steam dome, bell, whistle, and safety valves on top of the boiler.

[9] Among the running boards, there was a broad skirting mounted from the cab and firebox sides forward over the cylinders, then narrowing as turned into the pilot.

600 was equipped with Timken roller bearings and lightweight reciprocating parts on it axles, rods, pistons, crossheads, valve gear, and wrist pins, which provided the locomotive a smooth run and quicker acceleration.

[15] The result was an increase in the starting tractive effort of the main engine to 80,000 lbf (355.86 kN) (rendering the booster on No.

605–610, was delivered in 1943 at a cost of $168,550 each without streamlined casings and lightweight side rods, due to the limitations on the use of certain materials during the war; classifying them as the J1s.

[22] Additionally, all of the J class locomotives' streamlined front end, underneath the bullet nose, was given access holes to give ventilation for the cross-compound air pumps from behind.

[20] The class J locomotives were built with automatic lubricators at 220 points, allowing them to operate up to 1,300 miles (2,100 km) between refills.

610 made twelve round trip runs, hauling a 1,015-ton passenger train with 11 to 15 cars at speeds of more than 110 mph (180 km/h) between Chicago, Illinois and Crestline, Ohio on the Pennsylvania Railroad's Fort Wayne Division.

[29][30] Additionally, while pulling N&W's mainline passenger trains each month, the class J locomotives would take in turns to swap each other out in Roanoke and go to the Shaffers Crossing engine terminal for maintenance service and a washdown.

[33] Because of their power and speed, the class J locomotives were among the most reliable and efficient engines, running as many as 15,000 miles (24,000 km) per month, even on the mountainous and relatively short route of the N&W.

600 made its first revenue runs in early November, pulling the Cavalier and Pocahontas passenger trains, including SOU's Tennessean and Birmingham Special.

[51] During final revenue run in late 1959, it pulled three sponsored excursions from the Appalachian Power Company, the Washington Chapter of the National Railway Historical Society, and the Rail Museum Safari.