The rules that use the category "<unit-sing>" are:

<attach_detach_vehicle_command>

<attach_detach_vehicle_verb> <unit-sing>

<attach_detach_vehicle_verb> vehicle <unit-sing>

<basic_nl_command>

<unit-sing> <commander_phrase> <unit_command>

<unit-sing> <unit_command>

<zoomable_thing>

<unit-sing>