ighth ▁of ▁approximately ▁ 5 , 0 0 0 ▁Hol t ▁vehicles ▁used ▁by ▁all ▁Al lied ▁forces . ▁ ▁US ▁tank ▁pro tot ypes ▁▁ ▁In ▁Washington , ▁Pl iny ▁Hol t ▁super vised ▁the ▁design ▁and ▁building ▁of ▁ 1 0 ▁Ton , ▁ 5 ▁Ton , ▁and ▁ 2 . 5 ▁Ton ▁art illery ▁tra ctors ▁based ▁on ▁the ▁C ater p ill ar ▁craw ler ▁tra ctor ▁design , ▁at ▁the ▁request ▁of ▁the ▁Naval ▁Cons ult ing ▁board , ▁which ▁work ▁was ▁finally ▁completed ▁in ▁conj unction ▁with ▁the ▁engine ers ▁of ▁the ▁West ing house ▁company . ▁The ▁first ▁tank ▁Hol t ▁built ▁was ▁the ▁Hol t ▁Gas - E lect ric , ▁a ▁prototype ▁util izing ▁a ▁combined ▁gas oline - elect ric ▁prop ulsion . ▁A ▁Hol t ▁ ▁four ▁cyl inder ▁engine ▁produced ▁power ▁for ▁a ▁G . E . C . ▁generator , ▁which ▁in ▁its ▁turn ▁provided ▁current ▁to ▁drive ▁two ▁electric ▁mot ors , ▁one ▁motor ▁for ▁each ▁track . ▁It ▁did ▁not ▁progress ▁beyond ▁the ▁prototype ▁stage . ▁ ▁Hol t ▁also ▁produced ▁track ed ▁gun - car riers . ▁The ▁first ▁prototype ▁was ▁the ▁" C ater p ill ar " ▁Mark ▁I ▁Gun ▁Mount , ▁which ▁carried ▁an ▁ ▁how itzer , ▁we ighed ▁ ▁and ▁had ▁a ▁road ▁speed ▁of ▁ ▁to ▁. ▁Add itional ▁pro tot ypes ▁were ▁produced , ▁including ▁the ▁" Mark ▁II " ▁and ▁" Mark ▁III ", ▁and ▁the ▁" Mark ▁IV