The category "<establish_base_of_fire_command>" can be expressed as follows:

<establish_base_of_fire_command>

<set_up_verb> <base_of_fire_phrase>

<set_up_verb> <base_of_fire_phrase> <location_prep> <engagement_loc>

<set_up_verb> <base_of_fire_phrase> <location_prep> <engagement_loc> <open_fire_verb> <on_order>

<set_up_verb> <base_of_fire_phrase> <location_prep> <engagement_loc> targeting <on_prep> <enemy_loc>