(advance guard SUPPORT UNIT) says that UNIT plays the role of advance guard in the supporting a unit event SUPPORT. Specifically, there is a larger unit of which UNIT is a part, the larger unit has been assigned a task, and UNIT has been sent out ahead of the larger unit to ensure its ability to advance and carry out its task. SUPPORT is the event during which UNIT acts in this capacity, and temporally subsumes the instantiation of the larger unit's task (if there is such an instantiation). Note that it is incorrect to say that UNIT *supports* the larger unit directly; UNIT is either an support advance guard or an advance guard reserve, and the former class directly supports the latter class.