BL 8-inch Howitzer Mk. IV, Canadian War Museum, Ottawa, Ontario. The Breach-Loading 8-inch Howitzer in various Marks was a British artillery siege Howitzer mounted on a mobile carriages introduced in the First World War. These guns fired a 200 lb shell to 12,300 metres. Canada had two 6-gun batteries equipped with this Howitzer at the end of the First World War.