In War of the Three Powers, 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 thus non-promotable) units such as Spies, Engineers and MCVs except for Cryo Legionnaires in Uprising. This is still useful because these units can last slightly longer and if three Veteran Academies are owned, they can heal themselves.
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.