Some people deride the Poles for still having mounted cavalry units in WWII. The idea the these cavalry units charged tanks is a myth though. The cavalry charge was long out of practice by then, instead, they functioned as high-mobility infantry units.

In engagements, they performed much better than the German Panzer divisions they encountered, winning many of the engagements. Mechanized units got bogged down in the swamps and anywhere else that wasn’t hardtop road. They were less successful in engagements with German infantry.

Horse-mounted units would actually have been very useful in some engagements in Vietnam due to its terrain. And horses carried Green Berets into Afghanistan in the early invasion.