In World War II, equipment was needed to combat against heavily armoured tanks and tank destroyers. This came in the form of small, wheeled, and easily portable guns. At the start of World War II these were small calibre guns designed to tak eout lightly armour vehicles. But as the war progressed the guns increased in size and calibre. This developed into Anti-Tank guns to penetrate the frontal armour plates. Anti-aircraft guns were needed  to protect cities like London from German bombers.