Class Z-2 (Locobase 848)

Data confirmed by locomotive diagrams from 1900 hosted on http://www.nprr.org/Steam%20Diagrams/Forms/AllItems.aspx (7 Feb 2004) and NP Miscellaneous Steam Loco Diagrams supplied in May 2005 by Allen Stanley from his extensive collection.

An oddball 1910 design that was fitted with 655 sq ft of "reheater" and a feedwater heater with 401 2 1/4" tubes measuring 5' 3" long.

Rebuilt 192- & 1925,

Class Z-3 (Locobase 849)

Schenectady and Brooks built 21 of these big articulateds from 1913-1920 in three batches (4005-4014 in 1913, 4015-4019 in 1917, and 4020-4025 in 1920). Arch tubes contributed 41.6 sq ft of firebox heating surface.

They were widely used throughout the railroad. The 29 August 1913 Railway Age described Z-3 service as follows: "Between Helena and Blossburg a Class W-3 locomotive with a Class Z-3 helper is hauling 1,750 tons with no increase in coal over that formerly used by a Class W and a Class Z-1 handling 1,350 tons. This is an increase of 29.6 per cent in train load, with no increase in coal consumption.

"The new Class Z-3 Mallets are used on the Rocky Mountain and Seattle Divisions, four coal burners on the Rocky Mountain Division and six oil burners on the Seattle Division. The grades and trains on the Rocky Mountain Division are described above, these locomotives being used as helpers between Helena and Blossburg.

"The Seattle Division, from Ellensburg, Wash., to Auburn, Wash., is 105 miles long, crossing the Cascade Mountains through Stampede Tunnel west of Ellensburg at an elevation of 2,837 feet above sea level. These locomotives are handling 2,200 tons from Auburn to Ellensburg at a speed of from eight to 14 miles per hour, on a total oil consumption of 2,645 gallons. From Auburn to Lester, a distance of 43 miles, the average grade is one per cent. From Lester to Easton, a distance of 24 miles, there is a ruling grade of 2.2 per cent for ten miles. [A] Class Z Mallet helper ... is used from Lester to Martin. Westbound, the Z-3 locomotive handles a time freight of 1,900 tons from Ellensburg to Auburn on 1,726 gallons of oil, having a Class Z (2-6-6-2) Mallet helper on the 2.2 per cent grade."

See also Railway Age (21 Oct 1921). Drury (1993) notes in a caption that the 40"-diameter cylinders, which look like trash barrels mounted horizontally on the front of the engine, "signify great tractive effort and little speed." And in fact RA noted that the maximum horsepower was generated at 10.6 mph.

Class Z-4 (Locobase 850)

Data from 1929 NP locomotive diagram book supplied in May 2005 by Allen Stanley from his extensive collection.

Identical to the USRA's heavy articulated design. Built at Richmond. None of the NP diagrams showed the firebox heating surface separately, so Locobase took the value from the USRA entry (Locobase 330).