In 1928, the Boston & Maine procured their first 20 Berkshire-type locomotives from Lima. This meant a leading axle, four driving axles and a two-axle bogie under the firebox. Thanks to the bogie, the grate area could be exactly 100 square feet. After the 20 locomotives of the class T-1a, another five were ordered in the following year and classed T-1b. These were slightly heavier than the T-1a, which were later upgraded to the same level.
Because the adhesive weight was relatively low compared to the power of the engine, the maximum cutoff was set at 60 percent. The actually achieved starting tractive force therefore deviates from the result of the formula usually used, as this assumes a cutoff of 85 percent. An additional 12,000 pounds of traction came from a booster driving the rear axle of the bogie. A special feature of the locomotives was the Coffin feedwater heater, which lay in a semicircle above the smokebox.
The locomotives were unpopular in operation, as the bogie was often the cause of problems. Because the weight of the firebox rested on it, high forces acted on the boiler when running through curves. In addition, the bogie tended to derail when reversing.
In view of the problems, the Boston & Maine was able to sell ten engines to the Southern Pacific and seven to the Santa Fe during World War II. The Santa Fé gave the locomotives a rebuild that increased boiler pressure to 270 psi and used smaller diameter, longer stroke cylinders. These were able to prove themselves in service until 1954, while the others had already disappeared in 1949.
