In the days of sail
were armed with smooth-bored guns
firing shot weighing anything from 2.7 to 19.1 kg (6 to 42 pounds). These guns were fired through gunports cut into the ship's sides. If one ship was being chased by another, none of these guns could be brought to bear. But if a gun could be fired backwards, it might disable the other craft and stop pursuit.
To overcome this problem shipbuilders began to cut gunports in the rear of the ship. The design
of sailing warships did not permit many of these. The largest ships would mount only four guns. Because such guns were used during chases they were known as chasers. Those at the front were bowchasers, those at the rear were stern-chasers.