The DRU-H-R is a positioning and orienting sub-system for use on weapon systems. Electronic odometer signals and GPS position and time data may optionally aid it. The DRU-H-R may be used in a variety of host system configurations.

The DRU-H-R covered by this specification is military unique. It is mounted to the gun trunnion of the M109A6 Self-Propelled Howitzer and must operate through the extreme levels of gunfire shock. It also must operate after exposure to the nuclear, biological and chemical warfare environments and subsequent decontamination. Commercial inertial navigation systems are not designed to withstand such extreme environmental conditions and would experience catastrophic failure. The DRU-H has extensive electronic data interchange requirements, which must be retained by the DRU-H-R for backward compatibility with the M109A6, AN/TPQ-36 and AN/TPQ-37. There is no commercial specification or standard covering the command and message formats.