As World War I progressed, it was replaced in the home air defence of England (against German heavy bombers) by the more powerful QF 3 inch 20 cwt gun, but continued in all other theatres. It was usually deployed mounted on medium lorries such as the Thornycroft Type J with a speed of 18 miles per hour, in sections of 2 guns.
On the Western Front they were typically used to protect troop columns, airfields, bases, supply dumps and observation balloons.
As important as the raw performance of the gun itself was the new technology being developed to allow fast calculation of aircraft height and predict where it would be when the shell arrived near it. Modern aircraft could fly at over 100 miles per hour and to 20,000 ft (much lower over the battlefield) by 1918, which made the old reliable artillery shooting techniques obsolete. The shell took 10.1 seconds to reach 5,000 ft (1,500 m) fired at 25° above horizontal, 15.5 seconds to reach 10,000 ft (3,000 m) at 40°, 22.1 seconds to reach 15,000 ft (4,600 m) at 55°. Hence the aircraft position had be calculated 10–22 seconds in advance and fuzes needed to be set to explode at the correct height.
By the end of World War I, a 13 pounder AA Section was accompanied by 2 Wilson-Dalby Trackers with a rudimentary electronic computer to provide tachymetric prediction, a UB2 rangefinder, a Height/Fuze Indicator (HFI) and an Identification telescope. German fighters countered by attacking at low level—a few hundred feet. AA guns would continue to fire but the shells would then explode over the heads of those they were defending. But it brought attacking aircraft within range of defensive machine guns. Few aircraft were actually directly shot down, each requiring an average 4,000–4,500 shells, but guns were often employed in aerial barrages to deny an airspace to aircraft rather than to simply shoot down individually targeted aircraft. Brigadier Routledge notes that "in the BEF [i.e. on the Western Front] stress was laid on long-range deterrent fire; indeed in Fourth Army this was the BRA's stated policy. 'Kills' were therefore less common. Moreover, gun and fighter zones were not separated, as in Britain, and this made set plans for action less workable".
Routledge further comments that in World War I British cooperation between infantry and anti-aircraft sections was generally rudimentary. However, he points out a successful integration in the Allied advance on the Piave in Italy in late 1918, where S and V Batteries of 4th AA group used their 13 pdr 9 cwt guns to provide mobile air and ground fire in close support of infantry. This tactic later became common in World War II.
At the end of World War I, a total of 306 were in service worldwide, 232 of these on the Western Front (out of a total 348 AA guns there).