Why can't I station the Quarter Master in the Barracks?

Combat heroes are placed in formation in the barracks to lead troops (not stationed via the station management building). To add heroes to the APC formations you must have completed the research items for each of the three placements. (3 rows of troops)

Each APC has a research tree, the first item unlocks the first hero position and then as you work your way though each tree you will unlock the other 2.