▁and ▁supplies . ▁The ▁C ủ ▁Chi ▁t unn els ▁were ▁used ▁particularly ▁during ▁the ▁T ế t ▁Off ensive ▁in ▁the ▁Vietnam ▁War ▁between ▁ 1 9 6 8 ▁and ▁ 1 9 6 9 ▁by ▁Commun ist ▁V iet cong ▁guer illas , ▁who ▁made ▁these ▁in h osp itable ▁but ▁st ur dy ▁t unn els ▁their ▁home , ▁and ▁transport ed ▁supplies ▁for ▁the ▁Off ensive ▁that ▁were ▁assemble d ▁through ▁them . ▁The ▁t unn els ▁contained ▁sleep ing ▁ch amb ers , ▁k itch ens , ▁class rooms , ▁well s , ▁and ▁medical ▁facilities . ▁In ▁order ▁to ▁maintain ▁the ▁flow ▁of ▁o xygen ▁from ▁the ▁surface , ▁the ▁V iet cong ▁would ▁clever ly ▁dis gu ise ▁air ▁v ents ▁as ▁seem ingly ▁natural ▁objects ▁like ▁term ite ▁m ounds . ▁However , ▁the ▁t unn els ▁were ▁far ▁from ▁home y ; ▁the ▁V iet cong ▁suffered ▁from ▁many ▁of ▁the ▁elements , ▁such ▁as ▁disease ▁and ▁ven om ous ▁insect s ▁and ▁animals . ▁Part icular ly ▁n erve - rack ing ▁to ▁the ▁V iet cong ▁were ▁the ▁massive ▁aer ial ▁bomb ard ment ▁from ▁B - 5 2 ▁bom bers , ▁which ▁could ▁usually ▁cave ▁in ▁port ions ▁of ▁the ▁t unn els ▁depending ▁on ▁their ▁depth s . ▁Non eth eless , ▁the ▁t unn els ▁stood ▁up ▁to ▁almost ▁everything ▁the ▁American ▁military ▁threw ▁at ▁them . ▁ ▁Rec ent ▁uses ▁ ▁North ▁Korean ▁t unn els ▁North ▁Korea