Tuhia he haere tonu mo tenei whitianga - Ko te Mark 3 he waahanga waenga taapiri i hoatu ki a ia te roa me te nekehanga o te 640 tana. Ahakoa tenei taumaha taapiri, he tere ake te kaipuke i te Tohu 1. I whakaaetia te Mk.3 i te 8 Paenga-whawha 1941, a i hangaia i roto i nga waahanga e rima. Ko te Mark 4 he poto ake, he maama ake i te Mk.3, engari he nui ake te rama () ana i hangaia mo nga mahi whakawhiti whakawhiti i te mea kaore i te whakamahi i te moana. I te whakamātautau i ngā mahi whakaeke o mua, pēnei i te whakaekenga kino a te kaihautū o Kanata ki Dieppe
I te 1942, ko te korenga o te kaha o te mahi i arahina ai ki te hiahia mo te roa o te roa i roto i nga waahanga o muri mai, ko te nuinga i hangaia i te United States.