▁I . ▁ ▁Some ▁t anks ▁had ▁already ▁picked ▁up ▁names , ▁either ▁nick names ▁or ▁from ▁project ▁names , ▁but ▁in ▁June ▁ 1 9 4 1 ▁the ▁Prime ▁Minister ▁W inst on ▁Church ill ▁asked ▁that ▁all ▁t anks ▁be ▁named . ▁ ▁The ▁number ▁can ▁be ▁used ▁for ▁up gr ades ▁to ▁the ▁tank ▁( syn onymous ▁with ▁a ▁second ▁Mark ▁design ation ), ▁but ▁can ▁also ▁be ▁used ▁for ▁different ▁cap ability ▁packages , ▁for ▁instance ▁the ▁fitting ▁of ▁a ▁different ▁gun ▁or ▁engine . ▁ ▁This ▁isn ' t ▁necessarily ▁a ▁ref in ement ▁or ▁improvement , ▁it ' s ▁simply ▁adapted ▁to ▁a ▁different ▁need ▁or ▁manufact uring ▁technique . ▁ ▁They ▁are ▁all ▁based ▁on ▁the ▁same ▁design ▁of ▁tank ▁however , ▁whereas ▁the ▁mark ▁of ▁tank ▁is ▁applied ▁to ▁evolution s ▁of ▁the ▁tank ▁design / spec ification . ▁ ▁For ▁example , ▁Valent ine ▁and ▁Church ill ▁both ▁mounted ▁a ▁series ▁of ▁different ▁tur rets , ▁some ▁of ▁which ▁were ▁improvements , ▁while ▁others ▁were ▁different ▁methods ▁of ▁manufact uring . ▁ ▁Valent ine ▁was ▁fitted ▁with ▁both ▁pet rol ▁and ▁dies el ▁engines ▁determined ▁by ▁avail ability ▁and ▁manufact urer . ▁ ▁C rom well ▁and ▁Church ill ▁t anks ▁mounted ▁the ▁ 7 5 mm ▁gun ▁and ▁ 9 5 mm ▁how itzer ▁for ▁different ▁purposes . ▁ ▁All ▁were ▁given ▁different ▁numbers ▁to ▁identify ▁the ▁different ▁variants . ▁ ▁T ank ▁production ▁by ▁model ▁ ▁T ank , ▁Infantry , ▁M