The last mounted cavalry unit in US service to see action was the 26th Cavalry (Phillipine Scouts), a regiment of Filipino troopers with American officers in the Philippines, stationed at Ft Stotsenburg, Luzon. They fought both mounted and dismounted against Jap invasion troops, once attacking Jap tanks December 1941 to February 1942. According to a Bataan survivor interviewed in the Washington Post (10 Apr 1977) starving U.S. and Philippine troops ate all the regiment's horses.
In Italy, 3 ID captured enough German artillery horses to field a Provisional Recon Troop (Mounted)
In Burma, 1944-45, a Texas National Guard Cavalry Regiment of the Mars Task Force stayed in the bush for months supplied by air drops and a large mule train.
Last mounted cavalry unit...129th Cavalry Squadron, activated 1 May 1944 for tactical instruction at Cavalry School; deactivated 6 Feb 1945.
Last mounted (horse or mule) US Army unit...4th FA Bn & 35th QM Pack Co, both deactivated at Ft Carson, CO, 15 Feb 1957.
There are Mounted Color Guards and Demonstration Units of platoon size or less at Forts Riley, Carson and Huachuca. The Old Guard 3rd Infantry keeps a few horses to pull caissons carrying caskets to military funerals at Arlington National Cemetary
Grey's Scouts were a mounted infantry battalion of the Rhodesian Army which was very effective against terrorists in the late 1970's.
Our Green Beanies are carrying on a glorious tradition while making some history of their own. I hope some American T. E. Lawrence writes about it.