Caterpillar D7

The Caterpillar D7 is a medium bulldozer manufactured by Caterpillar Inc.. The first D7 appeared in 1938. The D7C came next in 1955. The D7D came in 1959. The 160 hp  D7E in 1961. The 180 hp  D7F 1969.The 200 hp D7G in 1974.The 215 hp in 1986.The D7H was the first D7 to come with the exclusive elevated drive sprocket undercarriage.The D7R replaced the D7H in 1996 with the current D7R Series 2 replacing that.

In March 2008, at Conexpo 2008 held every 3 years in Las Vegas, Caterpillar introduced the D7E. This 235 hp D7E comes with an electric drive system powered by a 537cid C9.3 diesel engine. The C9.3 powers a generator that turns out electricity that will supply power to a pair of AC drive motors. Compared to the Caterpillar D7R Series II, the D7E is projected to deliver 25 percent more material moved per gallon of fuel, 10 percent greater productivity and 10 percent lower lifetime operating costs.

The D7R Series II at 240 hp power and an operating weight of 25 tons, is in the middle of Caterpillar's track-type tractors, which range in size from the D3 57 kW (77 hp), 7 t (8 short tons), to the D11 698 kW (935 hp), 112 t (124 short tons). It is primarily used to move material short distances or through challenging terrain. The vehicle is powerful, yet small and light 16 to 20 t (18 to 23 short tons) depending on configuration). This makes it ideal for working on very steep slopes, in forests, and for backfilling pipelines safely without risking damage to the pipe.

An agricultural version without the blade and rippers is commonly used by farmers.

The US Army used armored D7G to clear mine fields and unarmored D7G and D7H for earthworks. The armor was developed by the Israel Military Industries (IMI). Later, the US Army developed a remote controlled version of the D7G for mine-clearing applications.

The United States Marine Corps has replaced its fleet of D7Gs with John Deere's 850J MCT in 2009

The Egyptian Army operates an unknown number of armoured D7R II.

The current model is the D7R Series 2 Track-Type Tractor and will be replaced by the D7E in early 2009.

Dozer blades
The dozer blade on front of the tractor usually comes in 4 varieties: Various other blade types are used including landfill U-Blades, woodchip U-blades, and two-way blades for work inside the holds of ships.
 * 1) A Straight Blade ("S-Blade") which is short and has no lateral curve, no side wings, and can be used for fine grading.
 * 2) An Angle Blade: The most common type that is used on Canada and Bolivia. Angle Blade is held by an U shape frame that has 3 holes on each side, to set the blade to 3 positions: to the right, center and left.
 * 3) A Universal Blade ("U-Blade") which is tall and very curved, and has large side wings to carry more material.
 * 4) A "S-U" combination blade which is shorter, has less curvature, and smaller side wings.