Continuing it's tradition of fast passenger Pacifics, in December 1934 the Boston & Maine took delivery of five Lima-built Class P-4a 4-6-2s. The "Super" Pacifics were definitely in the Lima "Super-Power" mode. With a skyline casing, smoke deflectors, oversized sand dome and shrouded pilot-mounted air pump, a P-4a certaily looked it's part! The B&M named these locomotives, proudly displated on a running-board name plate. During the early 1940's the skyline casing and smoke deflectors were removed, and in 1944-45 a second pilot-mounted air pump was installed. The P-4a class was good enough to make the B&M order five more as Class P-4b, delivered in March 1937. These were delivered without skyline casings or smoke deflectors. All but #3713 were scrapped by 1955.

Lima-built (1934), Boston & Maine #3710-3714, Class P-4a 4-6-2 Pacific, 12,000-gal/18-ton tender, Coffin feedwater heater, Standard HT stoker, Elesco superheater, American multiple front-end throttle and 80" drivers.

Lima-built (1937), Boston & Maine #3715-3719, Class P-4b 4-6-2 Pacific