It was a larger and modified version of the earlier, experimental, UR GC class.

[2] The first batch of GD class engines entered service on the UR in 1923.

[3] Heavier rail had been laid on the UR main line in preparation for their arrival.

[4] Further batches entered service progressively, including after the UR was renamed the Kenya-Uganda Railway (KUR) in 1926.

[4] Media related to UR GD class at Wikimedia Commons