", ▁which ▁depart ed ▁slightly ▁from ▁the ▁prior ▁models . ▁Pl iny ▁completed ▁a ▁pre lim inary ▁study ▁of ▁a ▁one - man ▁tank ▁which ▁was ▁later ▁built ▁by ▁the ▁Ford ▁company . ▁The ▁pro tot ypes ▁were ▁rejected ▁after ▁tri als ▁found ▁that ▁their ▁size ▁and ▁man eu ver ability ▁did ▁not ▁offer ▁the ▁relative ▁ag ility ▁required ▁by ▁a ▁tank ▁for ▁cross - country ▁travel . ▁ ▁Hol t ▁also ▁produced ▁a ▁ 7 5 mm ▁self - prop elled ▁gun ▁that ▁could ▁travel ▁at ▁, ▁exceed ing ▁the ▁military ▁requirement ▁of ▁, ▁and ▁clim b ▁a ▁ 4 5 ˚ ▁slope . ▁Before ▁the ▁work ▁could ▁be ▁completed , ▁the ▁Arm ist ice ▁was ▁signed ▁and ▁the ▁war ▁ended . ▁Self - prop elled ▁art illery ▁did ▁not ▁gar ner ▁attention ▁again ▁until ▁the ▁end ▁of ▁the ▁ 1 9 3 0 s , ▁just ▁before ▁World ▁War ▁II . ▁ ▁During ▁ 1 9 1 9 , ▁Pl iny ▁Hol t ▁returned ▁to ▁Stock ton ▁and ▁the ▁Hol t ▁company ▁where ▁the ▁" Mark ▁VII " ▁was ▁designed ▁and ▁built . ▁It ▁had ▁a ▁ ▁gun ▁mounted ▁and ▁ran ▁at ▁a ▁top ▁speed ▁of ▁. ▁In ▁ 1 9 2 1 , ▁the ▁company ▁finished ▁the ▁" Mark ▁VI ", ▁which ▁achieved ▁spe eds ▁of ▁up ▁to ▁ ▁on ▁a ▁test ▁run ▁from ▁Stock ton ▁to ▁San ▁Francisco ▁and ▁back . ▁ ▁British ▁acknowled g ement ▁▁▁ ▁In ▁April ▁ 1 9 1 8 , ▁British ▁Colonel ▁Ernest ▁Sw