What US Horse Cavalry units served during World War 2?

Answer 1

None really, at least not as horse cavalry. The Army had two horse cavalry divisions when the war in Europe began in 1939. Two days after the war started, General Marshall took over as Chief of Staff of the US Army and began to modernize, and the horse cavalry divisions were deactivated in 1940. Their personnel, with accumulated skills and unique abilities, were distributed throughout the army. This was perhaps premature, because especially in Italy, the Army was forced to use mules and donkeys to haul supplies up the steep, roadless Italian mountains, and to bring the wounded down. But the skilled cavalry personnel were scattered beyond recovery.

But, the units were soon brought back to life, though not as horse cavalry. The First Cavalry Division fought in the Pacific, as "dismounted" cavalry (they had no horses). The unit continues in existence today, based at Fort Hood, Texas, as the "Air Cavalry", with liberal provision of helicopters. The unit is perpetuated largely to continue the existence of its storied regiments, the 1st, 5th and 7th Cavalry Regiments. The 1st Cav is the old 1st Dragoons, among the first regiments of the US Army, dating back to the 1790s. The 5th Cav is the old 2nd Cavalry (the mounted regiments were all redesignated Cavalry and renumbered after the Civil War), of which Robert E. Lee was the original Lieutenant Colonel, Albert Sidney Johnston the original commander, and in which four out of the eight men to become full, four-star Confederate generals served in the 1850s. The 7th Cavalry is Custer's Regiment of Little Big Horn notoriety.

The 2nd Cavalry Division was also reconstituted just after the US got into WWII. It was a black outfit, with white officers, containing the famed old 9th and 10th Cavalry regiments, the traditionally black "Buffalo Soldier" units of the Great Plains in the late 1800s. It too saw action in the Pacific. In its first contact with the enemy, on Los Negros Island, the Division performed probably no worse than many new US Division on first entering combat. But parts of it did break and run, and opponents of integration and black combat troops in the Army pointed to this as proof that blacks were not fit for combat. The 2nd Cavalry Division was soon again deactivated.