ff1cce19_Game_Manual___Achron_Wiki__Function
[Method] Alt Right Click [Description] Hold the Alt key and right click on a unit [Function] 
(Only works if the unit is a subordinate) The selected unit is added to the current selection: If the unit's commander is not selected then it is selected, else if the unit's commander is selected, the unit's top-level commander is selected
Game Manual - Achron Wiki
Function