Horse traction was replaced early in the 20th century by the internal-combustion engine, which also was used to power the pump. The basic automotive hose carrier quickly assumed its modern form; it carries a powerful pump, a large amount of hose (usually about 1,000 feet, or 300 metres), and a water tank for use where a supply of water is not available. Specialized auxiliary vehicles were also soon developed, including water tank trucks for rural areas. The ladder truck (hook and ladder) mounts a ladder that may be capable of rapid extension to 150 ft, often with a large-capacity nozzle built into the top section. The older type of overlength ladder truck is equipped with steerable rear wheels for negotiating city streets. The main ladder is mounted on the truck's body; when it is to be raised into the air, the hinged main ladder and its sliding extensions are moved into place by a hydraulic pump. The ladder truck carries some 200 ft or more of ladders to be used from the ground. The snorkel truck, introduced by the Chicago Fire Department in 1958, is equipped with a hydraulically operated crane mounted on a turntable, for use in either fire fighting or rescue work. The rescue truck carries such specialized equipment as cutting and wrecking tools, gas masks and inhalators, portable lighting and smoke-ejection devices, chemical extinguishers, life nets, shortwave radios, and medical equipment.