In World War III, several new Tech Structures were seen. One of these was the Veteran Academy.
Capturing a Veteran Academy causes all units produced afterward to be promoted by one rank. Multiple Veteran Academies have a greater effect (two Academies cause units to be produced at Elite level, and three Academies make units Heroic.) This effect even includes unarmed (and completely non-promotable otherwise) units such as Spies, Engineers, MCVs, and sky knights (except for Cryo Legionnaires in Uprising). This was anyways useful because these units could now auto-heal themselves (If they reach the Heroic level, of course).
If a commander captures this tech building, all units of his allies will receive the promotion as well. If the building is lost, new units will not start as veterans anymore.