With World War II being the largest air war in history, it is not surprising that it also saw the greatest deployment of anti-aircraft artillery. In mid 1944 the combatants fielded about 300,000 anti-aircraft guns of varying kinds ­ between seven and eight guns for every front-line aircraft. The crews for these guns amounted to about one and a half million men, and a further two million played supporting roles in anti-aircraft units. Within this total are weapons in dedicated anti-aircraft units; anti-aircraft and dual-purpose armament on warships, support vessels and merchant ships; and weapons with a primary or secondary anti-aircraft role held by army units or attached to armored vehicles and small craft.

Figure 1 shows the number of anti-aircraft guns in use in each country in mid 1944. The total includes manually-loaded cannons, automatic cannons and heavy machine guns, but excludes rifle-caliber machine guns which, while of limited practical value against aircraft, were nevertheless held by many army units for anti-aircraft purposes. The total also excludes anti-aircraft rocket launchers. The 300,000 weapons can be divided into classes based on their caliber as shown in figure 2, while figure 3 shows the characteristics of each class.