The principle of continuous movement is perhaps the simplest and most obvious fact of an assembly line, dating back to Assyrian times, where there is evidence of a system of bucket elevators called the "chain of pots." Miners in medieval Europe also used these bucket elevators, and by the time of the Renaissance, engineers were becoming familiar with some form of the assembly line. In the fourteenth century, for example, the shipbuilding arsenal of Venice used moving lines of prefabricated parts to equip their war galleys. What may have been the first powered-roller conveyer system was introduced in 1804 by the British Navy's automatic production of biscuits or "hardtack." It used a steam engine to power its rollers. By the 1830s, the principle of continuous processing was starting to enter the consciousness of manufacturers, although it was by no means fully embraced until the 1870s in the United States. By then, the principles of division of labor and interchangeable parts had been successfully demonstrated by the American inventors Eli Whitney (1765-1825) and Samuel Colt (1814-1862).
The assembly line was first used on a large scale by the meat-packing industries of Chicago and Cincinnati during the 1870s. These slaughterhouses used monorail trolleys to move suspended carcasses past a line of stationary workers, each of whom did one specific task. Contrary to most factories' lines in which products are gradually put together step-by-step, this first assembly line was in fact more of a "dis-assembly" line, since each worker butchered a piece of a diminishing animal. The apparent breakthroughs in efficiency and productivity that were achieved by these meat packers were not immediately realized by any other industry until the American industrialist Henry Ford (1863-1947) designed an assembly line in 1913 to manufacture his Model T automobiles. Ford openly admitted using the meat-packing lines as a model. When the total time of assembly for a single car fell from 12.5 labor hours to 93 labor minutes, Ford was able to drastically reduce the price of his cars. His success not only brought automobile ownership within the grasp of the average person, but it served notice to all types of manufacturers that the assembly line was here to stay. The assembly line transformed in a revolutionary way the manner and organization of work, and by the end of World War I, the principle of continuous movement was sweeping mass-production industries of the world and was soon to become an integral part of modern industry.
The basic elements of traditional assembly line methods are nearly all the same. First, the sequence in which a product's component parts are put together must be planned and actually designed into the process. Then the first manufactured component passes from station to station, often by conveyor belt, and something is done or added to it. By the last station, the product is fully assembled and is identical to each one before and after it. This system ensures that a large quantity of uniform-quality goods are produced at a relatively low cost.
When manufacturers first implemented the idea of the assembly line, they enjoyed dramatic gains in productivity, and the consumer realized lower costs. However, the nature of work in a factory changed radically. Skilled workers were replaced by semi-skilled or even unskilled workers, since tasks had been minutely compartmentalized or broken down and each person was responsible only for assembling or adding one particular part. Manufacturers soon realized however, that not only were a great number of managers and supervisors required to oversee these laborers, but a high degree of preplanning on their part was absolutely essential. Overall operations had become much more complex and correct sequencing was essential. Thus, before actual assembly line production could begin, proper design of both the product and the assembly line itself had to be accomplished. Even the simplest tasks were critical to its overall success, and the apparently straightforward assembly line became a highly complex process when broken down and considered step-by-step.