The first bulldozers were adapted from farm tractors that were used to plow the fields. In order to dig water canals, raise earthen barriers, and do other earthmoving projects, the tractors were equipped with a large thick metal plates. This thick metal plate (it got its curved shape later) is called a "blade". The blade peels layers of soil and pushes the soil as the tractor advances. Sometimes a bulldozer is used to push another piece of earthmoving equipment known as a "scraper". The Fresno Scraper, invented in 1883 by James Porteous, was the first design to enable this to be done economically, at the same time removing the soil and depositing it in shallow ground.
Over the years, when engineers needed equipment to complete large scale earthmoving works, firms like the Caterpillar Tractor Company, Komatsu, Fiat-Allis, John Deere, International, Case, Leibherr, and JCB started to manufacture large tracked-type earthmoving machines. They were large, noisy, and powerful, and therefore nicknamed "bulldozer".
Through the years, the bulldozers got bigger, more powerful, and more sophistocated. Important improvements include more powerful engines, more reliable drive trains, better tracks, raised cabins, and hydraulic arms that enable more precise manipulation of the blade and automated controls. Some bulldozers are also equipped with a rear ripper claw in order to loosen rocky soils.
The most well known maker of bulldozers is probably the Caterpillar Tractor Company, which earned its reputation for making tough, durable, and reliable machines. Although these machines began as modified farm tractors, they became the mainstay for major civil construction projects, and found their way into use by military construction units throughout the world. Their best known model, the Caterpillar D9, was also used to clear mines fields and demolish enemy's structures.
Bulldozers have been further modified over time to evolve into new machines which are capable of working in ways that the original bulldozer can not. One example is that loader tractors were created by removing the blade and substituting a large volume bucket and hydraulic arms which can raise and lower the bucket, thus making it useful for scooping up earth and loading it into trucks. Other modifications to the original bulldozer include the reduction in size of the machine to permit it to operate in small work areas where movement is limited. There are also tiny wheeled loaders, officially called Skid-steer loaders but nicknamed "Bobcat" after the original manufacturer, which are particularly suited for small excavation projects in confined areas.
Nevertheless, the orginal earthmoving bulldozers are still irreplaceable as their tasks are concentrated in earthmoving, ground leveling and road carvings. The heavy bulldozers are mainly employed at the leveling of the terrain in order to make it fit to construction. The construction itself, however, is mainly done by small bulldozers and loader tractors.