The XRB class were built by Pacific National at its South Dynon Locomotive Depot.

They are mechanically similar to the XR class, but are B units without driving cabs.

[1] They were built to operate as booster units on standard gauge interstate freight trains between Melbourne and Perth, and has to be led by a locomotive with a conventional driving cab.

These units do not have hostler controls for moving them around yards and depots,[2] only being fitted with a dead engine device and park-brake button.

[1] As of October 2022, all three are stored at Progress Rail's Port Augusta Workshops.