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

<hmmwv>

hmmwv with a tow

hmmwvs with a tow

<i_f_v-sing>

brdm with a t

lar with a mortar

lav a t

lav with a mortar

<i_f_v-pl>

brdms with a t

lar with a mortars

lav a ts

lav with a mortars

<hmmwv-pl>

hmmwvs with a tow

<winged_aircraft_type-sing>

f and a eighteen

<defensive_position_phrase>

a <basic_defensive_position_phrase-sing>

<concealed_position>

a <concealed_position-not_det-sing>

<hmmwv-sing>

hmmwv with a tow

<winged_aircraft_type>

f and a eighteen

f and a eighteens

<firing_rate_measure>

rounds a minute

<i_f_v>

brdm with a t

brdms with a t

lar with a mortar

lar with a mortars

lav a t

lav a ts

lav with a mortar

lav with a mortars

<scale_number-gapsout_null-gapsin_null>

a thousand

a hundred thousand

<winged_aircraft_type-pl>

f and a eighteens