After the C, C-1 and C-2 class Pacifics, the Maine Central ordered the C-3 class machines. Three locomotives were delivered in 1917 and two more C-3Bs in 1924. Compared to their predecessors, they had larger cylinders and lower boiler pressure. To increase the traction they had a booster on the trailing axle. Usually they pulled express trains with ten to twelve cars.
They were rebuilt in 1933 and 1934 and received smaller cylinders which were compensated for by higher boiler pressure. They also received a new boiler, which showed changes especially in the firebox surface. Number 470 still exists today, owned by the New England Steam Corporation, which is having it restored in Ellsworth, Maine. It is scheduled to be completed in 2024.