By the 1920s the Northern Pacific Railroad needed bigger passenger locomotives. The NP had its motive power department work with the American Locomotive Company's design engineers to develop a new locomotive. They designed a new locomotive with a massive firebox that had a 115 square foot grate area supported by a four wheel trailing truck. It was the first locomotive with a 4-8-4 wheel arrangement.

ALCO delivered the first of 12 of these new locomotives in December of 1926, with the balance arriving early in 1927. Designated Class A, and assigned road numbers 2600 through 2611, they had 73" drivers, 28 x 30 cylinders, a boiler pressure of 210 psi, a tractive effort of 57,500 lbs and weighed 426,000 pounds. Later, the boiler pressure was raised to 240 psi which increased the tractive effort to 65,700 pounds. These were the first of this new wheel arrangement and thus were to be the namesake, with the name "Northern Pacific" selected which was very quickly shortened to just "Northern".

In 1930, the Timken demonstrator came to the NP. While being tested, it suffered crown sheet damage. The NP bought it, repaired it and put it on the roster as number 2626.

Ten Class A-2s (road numbers 2650 through 2659) came from the Baldwin Locomotive Works in 1934. These heavy "Northerns" had 77" drivers, 28 x 31 cylinders, a boiler pressure of 260 psi, a tractive effort of 69,800 lbs and a weight of 489,400 pounds.

In 1938, eight Class A-3s (road numbers 2660 through 2667) were delivered from Baldwin. The specifications for these locomotives were identical to the Class A-2s except that each weighed 2,400 pounds more.

The eight Class A-4s (road numbers 2670 through 2677) were delivered by Baldwin in 1941, and had the same basic specifications as the A-3s, but were different in appearance, with 14 wheel centipede tenders and vestibule cabs, and they were 1000 pounds heavier.

The last of the 4-8-4s purchased by the NP were the Class A-5s, which were built by Baldwin in 1943. This group of 10 (road numbers 2680 through 2689) were built to the same specifications as the Class A-4s, but turned out to be 16,200 lbs heavier. They were among the heaviest of all the Northern type locomotives ever built, at 508,500 pounds only the Santa Fe Class 2900s weighed more.

There are no surviving Northern Pacific Northerns.