For the U.S. Army in WW II, transportation of supplies, equipment and personnel was almost entirely based on motor vehicles. However mules continued to be used in certain circumstances for their ability to negotiate rugged terrain inaccessible by vehicles. Mules could negotiate jungle or mountainous terrain that no horse or vehicle could traverse. In North Africa, the mountains of Italy and jungles of Burma, mules made a significant contribution. Locally obtained donkeys and burros added capacity to Army mules shipped from the U.S.
Ed no note on this one but I am sure you are correct - Italy