The successor of the Mack B series,[2] the R was a heavy-duty truck (Class 8) with a conventional (bonneted) cab configuration.

As with its predecessor, the R was offered in a wide variety of configurations for a comprehensive array of vocational and transportation applications.

Though not the first truck to adopt a forward-tilting hood, the Mack R introduced several innovations, including an air-ride cab, an integral engine compression brake, and a drivetrain that reduced the need for an auxiliary transmission.

The U had an offset cab, coined the "Commandcab", that placed the driver's door in the same vertical plane as the side of the trailer.

To compensate for the offset cab the engine “doghouse” intruded into the passenger footwell but left the driver's position intact.

Like the RMM, the DMM was all-wheel-drive, but it had not only a short hood and offset cab but also a set-back front axle, requiring a model-specific fiberglass hood-and-fender arrangement.

With the introduction of the Maxidyne ENDT-675 in 1966, Mack offered a series of engines that provided better fuel economy and less driver fatigue.

[citation needed] The RL series was introduced in 1967, and in 1973 the R cab was given a makeover to include a deeper rear wall for more room and a new dashboard design.

These models, announced by Mack in 2003, included a special steering wheel, limited edition paint, badges chrome and embroidered seats.

This allowed operators to keep the mechanical portions of the older truck that may have not needed replacement and marry them with the much improved cab of the R. It is unclear of how many of these kits were sold and installed.

[citation needed] In conjunction with the US Air Force, Mack built a prototype heavy-duty hybrid electric av gas refueler in 2005.

According to the Air Force, "The vehicle operates with a diesel engine, an electric motor and a battery pack to optimize fuel efficiency.

Iran Kaveh established ties with Mack in 1963 to produce licensed built trucks including the R. Approximately 60% of the content being Iranian sourced.