ers ▁borrow ed ▁elements ▁and ▁ideas ▁from ▁the ▁British ▁V ick ers - C arden - Lo yd ▁light ▁tank ▁and ▁the ▁American ▁International ▁Har v ester ▁T A - 4 0 ▁agricult ural ▁tra ctor . ▁Their ▁design ▁goal ▁was ▁to ▁achieve ▁a ▁vehicle ▁capable ▁of ▁acting ▁as ▁a ▁military ▁( t ow ing ) ▁tra ctor ▁and ▁a ▁civil ian ▁agricult ural ▁tra ctor . ▁They ▁developed ▁two ▁vehicles ▁on ▁the ▁same ▁ch ass is ▁and ▁engine , ▁the ▁ST Z ▁NAT I ▁ 1 TA ▁( ST Z - 3 ) ▁agricult ural ▁tra ctor ▁and ▁the ▁ST Z ▁NAT I ▁ 2 TB ▁( ST Z - 5 ) ▁military ▁transport . ▁The ▁vehicles ▁were ▁submitted ▁for ▁trial ▁in ▁ 1 9 3 5 ▁and ▁were ▁approved ▁however ▁design ▁ref in ements ▁for ▁mass ▁production ▁were ▁continued ▁until ▁ 1 9 3 7 ▁when ▁mass ▁production ▁began . ▁ ▁Oper ational ▁notes ▁▁ ▁The ▁ST Z - 5 ▁was ▁designated ▁to ▁to w ▁division ▁level ▁to ▁corps ▁level ▁guns , ▁how itz ers ▁and ▁anti - air craft ▁guns . ▁ ▁This ▁prime ▁m over ▁was ▁pra ised ▁for ▁its ▁reli ability ▁and ▁good ▁cross ▁country ▁ability . ▁It ▁was ▁critic ized ▁for ▁having ▁low ▁power , ▁a ▁narrow ▁track ▁and ▁high ▁ground ▁pressure , ▁which ▁would ▁have ▁led ▁to ▁poor ▁performance ▁in ▁snow ▁and ▁mud . ▁ ▁A ▁small ▁number ▁of ▁these ▁vehicles ▁had ▁the ▁ 1 3 2 mm ▁ro cket ▁launch er ▁system ▁attached ▁( B