QF 13 Pounder 9 Cwt
The 13 pounder 9 cwt anti-aircraft gun became the standard mobile British anti-aircraft gun of the World War I era, especially in theatres outside Britain. 13 pounder referred to the weight of the shell, 9 cwt referred to the weight of the barrel and breech (9 x 112 lb = 1008 lb), to differentiate it from other varieties of "13 pounder".
Read more about QF 13 Pounder 9 Cwt: History, Combat Use, Performance