From verso of card: "An Anti-Aircraft Gun must have a high rate of fire and be capable of following the movements of the fastest bombing aircraft. The 3-inch gun shown . . . is mounted on a mobile platform for use with the Field Army. It can throw a 16-lb. shell to 20,000 ft. in 23 seconds and can fire 20 rounds in a minute. This gun has a crew of 8. It is towed by a tractor and has a road speed of 20 miles per hour. Territorial Units for Home Defence are equipped with this gun on a fixed platform. For some purposes it is being replaced by a new type, the 3.7 in., which has been in production for some months. Its 'ceiling' is considerably higher, and it throws a somewhat heavier shell."