A tugboat or tug is a marine vessel that manoeuvres other vessels by pushing or pulling them, with direct contact or a tow line. These boats typically tug ships that cannot move well on their own, such as those in crowded harbors or narrow canals, or those that cannot move at all, such as barges, disabled ships, log rafts, or oil platforms. Some are ocean-going, some are icebreakers or salvage tugs. Early models had steam engines, and modern ones have diesel engines. Many have deluge guns, which help in firefighting, especially in harbors.