They will be called upon to deal with freight trains of up to 900 tons over gradients considerably steeper than those of the Central Section—for example, the frequent stretches of 1 in 100 between Victoria and the Medway towns—and their running to fast schedules will include the haulage of the "Night Ferry", which may load up to as much as 700 tons, and fully-fitted trains of 30 or more heavy Continental train ferry wagons.
Source: wiktionary