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.