This class of ten 2-10-10-2 locomotives were actually rebuilt from more conventional 2-10-2 Baldwin-built locomotives by the Atchison, Topeka and Santa Fe Railway in 1911.

Although they appeared to have exceedingly long boilers, the barrel in front of the rear set of cylinders actually contained first a primitive superheater for further heating the steam before use; the steam was carried forward from the boiler proper by outside steam pipes as shown in the photograph. Also contained in this space was a reheater to give additional energy to the high-pressure exhaust before it was fed to the forward low-pressure cylinders.

In front of that, there was a feedwater heater, a space where cold water from the tender could be warmed before being injected into the water proper. This worked similarly to the boiler itself; the firetubes passed through the feedwater tank.

The experiment was decidedly unsuccessful, and the locomotives were rebuilt back to 2-10-2s during 1915–1918.

Specifications
Road numbers: 3000–3009
Driver diameter: 57 in (1.4 m)
Weight: 616,000 lb (279,400 kg = 279.4 t)
Tractive effort: 111,600 lbf (496 kN)
Boiler pressure: 225 psi (1.55 MPa)
Cylinder diameter: 28 in (710 mm) high pressure, 38 in (970 mm) low pressure
Cylinder stroke: 32 in (810 mm)

Virginian Railway class AE

This class of ten locomotives were built in 1918 by ALCO for the Virginian Railway. While suffering from the horsepower limitation of Mallets, which limited their speed, the locomotives had the highest tractive effort of any steam locomotives ever built. Due to size limitations en route, they were delivered without their cabs and the front, low pressure cylinders, which were installed on site. The low pressure cylinders and the boiler were both the largest diameter ever used on a US locomotive; the cylinders had to be tilted slightly upward to provide sufficient clearance.[1]

As can be seen in the photograph, the tenders fitted were unusually small; this so that they could use the Virginian's existing turntables.

This class were true Mallet locomotives, in that as well as being articulated between the forward, swinging engine unit and the rear fixed one, they were also compound locomotives; the rear, high pressure cylinders exhausted their steam via a long pipe into the huge front cylinders. Like many compound locomotives, they could be operated in simple mode for starting; high pressure steam could be sent straight to the front cylinders at low speed, for additional tractive effort.

Unlike some other giant locomotives of the period, the immense boilers could generate enough steam to make them a success on the slow (8 mph or 13 km/h) coal trains for which they were built. They remained in service until the railroad electrified in 1952 and could be considered the ultimate drag era locomotive.