In 1988, Caterpillar produced their 25,000th elevated-drive-sprocket track-type tractor, a D9N. The 405 hp (302 kW) D9R replaced the D9N in 1996. The 410 hp (310 kW) D9T replaced the D9R in 2004. The D9T has a low-emissions ACERT diesel engine. The current model is the D9T; however, older models such as the D9R, D9N, and D9L are still commonly used. The L, N, R, and T models of the D9 are visually very similar, differing primarily in the design of their internal systems.
The D9L was replaced by the 520 hp (390 kW) D10N in 1987. The 370 hp (280 kW) D9N replaced D8L in 1987. The main difference between the D9T and the D9R is the installment of the new Cat C18 ACERT inline-six engine in the D9T vs the V8 3408 HEUI in the D9R. The D9R has clutch and brake steering, while the D9T has differential steering. The D9L is the most powerful D9 in history, with a flywheel power of 460 hp. The D9L is also the heaviest D9 in history at 130,000 lbs.
The D9's primary working tools are the blade, affixed to the front and controlled by four hydraulic cylinders, and an optional ripper, which can be attached to the back. The blade is mainly intended for earthmoving and bulk material handling: pushing up sand, soil, and rubble. It also can be used to push other heavy equipment such as earthmoving scraper pans, and in military applications, main battle tanks. The dozer blade usually has three variants:
