The rules that use the vocabulary item "direction" are:

<i_f_v-sing>

opfor artillery battalion fire direction center

opfor artillery battery fire direction center

<i_f_v-pl>

opfor artillery battalion fire direction centers

opfor artillery battery fire direction centers

<specific_vehicle_type-pl>

command post carrier fire direction centers

<specific_vehicle_type-sing>

command post carrier fire direction center

<i_f_v>

opfor artillery battalion fire direction center

opfor artillery battalion fire direction centers

opfor artillery battery fire direction center

opfor artillery battery fire direction centers

<specific_vehicle_type-not_creatable-pl>

command post carrier fire direction centers

<specific_vehicle_type-creatable-sing>

command post carrier fire direction center

<specific_vehicle_type-not_creatable-sing>

command post carrier fire direction center

<specific_vehicle_type-not_creatable>

command post carrier fire direction center

command post carrier fire direction centers