To carry heavier express trains, the Norfolk & Western designed the class J, which had a 4-8-4 wheel arrangement and distinctive streamlined casing. It was characterized by a bullet nose, a skyline casing on the top of the boiler and skirting on the running boards. It is considered the most powerful Northern ever built, surpassing the New York Central's Niagara. The boiler output was probably in the region of around 6,000 hp. 

A good compromise between high tractive power and high speeds was chosen with a driver diameter of only 70 inches, a very precise counterbalancing and a very rigid layout of the chassis. Although the wheel diameter of 70 inches would, according to the rule of thumb, only be sufficient for a top speed of around 70 mph (113 km/h), theoretically they could reach up to 140 mph without causing damage to the locomotive and tracks. In reality, with 15-car trains they reached speeds of around 110 mph (177 km/h). At the same time, stopovers were reduced by the automatic lubrication system, which served 220 points and only had to be refilled every 1,300 miles. 

The first five were built in 1941 and 1942 with streamlined fairing and lightweight coupling rods. Due to the war, the next six had to be built in 1943 without these features. They were only retrofitted after the end of the war. Three more followed in 1950, bringing the total to 14. When the most important express trains were dieselized in 1958, they were used about one additional year in freight service. 611 was saved from scrapping and has been back in use since its last overhaul in 2015 and is one of the biggest stars among North American steam locomotives.