A railroad car is a vehicle used for transporting cargo or passengers on a rail transportation system. Often, many railroad cars are grouped together; this grouping is called a train. Some kinds of railroad cars, usually passenger cars, can operate autonomously, but most need to be attached to a locomotive. A locomotive is a railroad car that provides movement to the train and usually has no payload of its own.
The passenger car is a common type of railroad car, as many people like to travel by rail because of the low price and convenience. Modern passenger cars often come equipped with internal heating, air conditioning, and toilets. For long-distance journeys, many trains with passenger cars also include dining cars and entertainment cars to make the journeys more bearable or even entertaining. Some even include sleeping cars that sometimes have small bedrooms for the convenience and comfort of their passengers.
Another common kind of railroad car is the freight car, which is used to carry a wide variety of different objects over land relatively quickly and cheaply. Freight cars are often used to carry components to various mechanical devices such as automobiles and aircraft. They are also commonly used to carry raw materials from the area they are extracted from to the factory or plant where they are refined or used to make products. Some cars, known as tank cars, are used to transport liquids and gases. Public and private militaries often use trains to transport military supplies where they are needed.
Almost every railroad car in a train is a "revenue car," meaning that it bears a cargo that makes money for the railroad. Railroad companies also have "non-revenue cars," which mostly include maintenance vehicles for use on the railway. Freight cars and passenger cars are both considered revenue cars, as passengers and companies pay for the use of the cars.
Militaries also use railway cars for defensive purposes, as well. Armored railway cars can be mounted with a wide variety of weapons such as machine guns, anti-air guns, and anti-tank weapons. Others are equipped with armored sleeping quarters for troops and are used for transporting them across distances. During the cold war, the Soviet Union even used train cars as mobile missile silos, effective for transporting missiles to optimal launch positions. Military use of trains resulted in the sabotage of railroad tracks by opposing military forces, as such sabotage could damage the transportation infrastructure of a military until the supplies needed to repair the tracks could be acquired.