Introduced in 1935, the German 88 mm gun became perhaps the most feared artillery weapon of the war. Widely used as a tank gun, it was also a powerful antitank gun and a coast defense and antiaircraft weapon. With a practical ceiling of 35,000 ft, the 88 posed a great threat to enemy bombers. A 105 mm gun also saw widespread use, and in 1942, with Allied bombing intensified, Germany fielded a 128 mm gun as an interim system (pending development of a superheavy 150 mm gun, which, however, never entered service). Lighter German antiaircraft guns ranged from 20 mm to 55 mm. Germany used 20 mm and 37 mm antiaircraft guns in a variety of configurations on several motorized platforms. The effectiveness of German antiaircraft defenses was reduced by a lack of precision radar control (RPC) systems and the fact that its antiaircraft projectiles lacked proximity fuses. The Italians also used a wide range of antiaircraft guns up to 90 mm in size.
Beginning in 1938, the British produced a 3.7-inch gun, which many came to believe was their best gun of the war. It had a ceiling of 28,000 ft. Its effectiveness was greatly increased by the introduction of RPC in 1944. This combination of radar, predictors, and proximity-fused ammunition gave it a high rate of success against German V-1 flying bombs. The U.S. Army began to replace its 3-inch gun with a 90 mm gun in 1940.
The Soviets also employed a wide range of antiaircraft weapons. They reproduced both the Swedish Bofors 25 mm and 40 mm guns, retooling the latter to fire a 37 mm projectile. The largest Soviet field antiaircraft weapon was the 76.2 mm gun; for home defense the Soviets relied on the 85 mm gun. Produced in large numbers, it was the principal Soviet antiaircraft gun of the war. As was the case with the smaller 76.2 mm gun, the 85 mm piece saw widespread service as main tank armament. The Soviets claimed that antiaircraft guns shot down 2,800 Axis aircraft, 40 percent of the total downed.
Operating on the generally held belief in the 1930s that bombers would always get through, the British focused their aviation efforts on developing a strategic bomber force at the expense of air defense. At war's outbreak, antiaircraft artillery was directed by predictors that followed the path of aircraft mechanically; they were useless at night or in poor visibility. Although all major powers experimented with new detection devices, the British made the primary strides in the field of operational radar. This interception device established the height, course, and speed of enemy aircraft. Throwing up shell barrages through which aircraft flew was no more successful as a tactic in World War II than it had been in World War I, but ground-fire threats increased substantially when the speed and height of a bomber stream could be ascertained by radar.
In the autumn of 1939, Britain still had only 540 antiaircraft guns larger than 50 mm. During the Battle of Britain, antiaircraft artillery took second place to fighter aircraft. Most sources place the number of aircraft shot down by antiaircraft artillery at fewer than 300 of the nearly 1,800 Luftwaffe planes destroyed. Yet ground fire forced aircraft to higher elevations, unnerved aircrews, and diminished bombing accuracy.
Flak was the principal defense against night attack. Night fighters were still being developed, although the requisite technology would evolve rapidly. Artillery sighting was largely visual until October 1940, when the British began to equip their forces with gun-laying radar, which increased the accuracy of artillery fire in all weather.
Reliance in Britain on lesser-trained territorial forces for antiaircraft defense foreshadowed personnel difficulties the Axis powers would later encounter in the war. Experienced men usually deployed to distant fronts or to sea, and so air defense depended on women, those too old to qualify for military service, or the physically restricted. During the war about 70,000 women served in British antiaircraft units.
When the Royal Air Force (RAF) and U.S. Army Air Forces (USAAF) strategic bombing campaigns gained impetus in 1942, German flak posed a serious threat. Aircraft coming in below 8,000 ft often suffered grievous losses from ground fire. Damage from flak continued to rise in the air war, and gunfire from the ground shot down more Allied bombers than did fighter aircraft.
Technological developments moved at a staggering pace as the fighting continued. By 1941, German flak units began deploying incendiary shells, gun-laying radar, and grooved projectiles that fragmented into small pieces, causing dreadful damage to aircraft. By 1943, most antiaircraft artillery shells had been converted from powder to mechanical fuses. Flashless propellants augmented the efficiency of the guns, as did automatic fuse-setters that improved accuracy and amplified the rate of fire two or three times. Use of electric predictors became fairly common. In 1944, the Germans introduced double fuses, both contact and timed, that boosted the efficacy of guns severalfold. By then, the Allies were customarily installing the U.S. Navy–developed proximity fuses in their shells, a technology the Germans never successfully employed.
For all that, the Germans put to trial several innovative antiaircraft techniques, such as squeeze-bore and sabot mechanisms designed primarily to increase the muzzle velocity of guns. During the course of the war, Germany developed four types of flak rockets, some guided, some not. The effect of flak rockets was in the main psychological, though, since German forces lacked operational proximity fuses, and radio-controlled guidance systems were rudimentary and subject to degradation.
In several urban areas, such as Berlin, Vienna, and the "flak alley" around Köln, Germany constructed large flak towers to serve as gun platforms. Some covered an entire city block and were more than 130 ft high (corresponding in size to a 13-story building) with reinforced concrete walls up to 8 ft thick. Batteries sited on the roofs mounted heavy antiaircraft artillery and multiple-barreled pom-pom cannon in the structures' turreted corners.
As the war progressed and Allied air raids occurred almost daily, German antiaircraft defenses faced challenges in growing measure. The quality of flak personnel plummeted as youngsters, women, disabled veterans, foreigners, and even prisoners of war serviced the artillery. At war's end, nearly half of all German gun crews were auxiliaries or civilians. Ammunition shortages manifested themselves in a big way in 1944, necessitating firing restrictions during air raids. Shortages would eventually reduce firing potential by more than one-half.
Nonetheless, German flak units caused about one-third of Allied aircraft losses and inflicted at least two-thirds of total aircraft damage through 1944. As German fighter protection became weaker, antiaircraft artillery invariably took on a larger role, continuing to impair Allied aircraft and to degrade bombing accuracy. According to U.S. reports, the USAAF lost 18,418 aircraft in European combat, 7,821 of them downed by flak. Follow-on studies credited antiaircraft artillery for as much as 40 percent of bombing errors.
After the June 1944 Allied invasion of Europe, Germany launched its V-1 buzz-bomb campaign in earnest. These low-altitude weapons, flying at nearly 400 mph, were tricky to locate and even harder to down. Fighters had little time to spot and destroy a buzz bomb. Antiaircraft artillery constituted the final line of defense against the V-1s.
Increasing motorization of land forces fostered a need for self-propelled antiaircraft artillery. Although U.S. ground forces used the .50 caliber Browning machine gun in various configurations for basic air defense, these were frequently mounted with the 37 mm antiaircraft gun, so the latter could aim with the Browning's tracer fire. After 1943, the army's chief heavy antiaircraft artillery piece, the 90 mm gun, was often mounted on a multipurpose carriage for antiaircraft or field artillery use. In early 1944, the army adopted the 120 mm antiaircraft stratosphere gun, which was nearly twice the size and weight of the 90 mm fieldpiece.
Beginning in 1940, the U.S. Navy devoted considerable attention to improving its antiaircraft defenses. Experience showed that 20 mm cannon of Swiss design were many times more effective against aircraft than machine guns. By 1945, the navy had deployed about 13,000 20-mm artillery tubes aboard ship and had inflicted nearly one-third of all Japanese aircraft losses with these weapons. In due course, the navy deployed some 5,000 40-mm guns of Swedish design in single, dual, and quad mounts. Also widely used shipboard was the 5-inch/38-caliber dual-purpose—that is, antiaircraft and antiship—gun, and some 3,000 were eventually mounted on ships. Proximity fuses in the 5-inch weapon greatly increased antiaircraft effectiveness.
Throughout the war, technological constraints and manufacturing hindrances beset Japanese antiaircraft-artillery capabilities. In 1941, the Japanese deployed just 300 guns in defense of the home islands, and by 1945, even in the face of the American air onslaught, Japan had only 2,000 guns earmarked for homeland defense. The standard Japanese antiaircraft gun throughout the war was the 75 mm type that first saw service in the 1920s. In the Japanese navy, the 25 mm was the standard light antiaircraft gun, and the 5-inch was the standard heavy. Some 500 heavy artillery pieces were committed to the defense of Tokyo by 1944, but fire control and radar capabilities for most weaponry remained inadequate.
Compared with that of the Germans, Japanese flak was far less effective against Allied air attack. During the entire war, Japanese antiaircraft artillery was credited with destroying just 1,524 American aircraft. Japanese naval vessels, perennially lacking in shipboard antiaircraft defense, suffered accordingly.
In sum, during the war, flak was often quite lethal and cost-effective, downing many enemy aircraft and complicating air missions. It made low-altitude bombing and strafing operations a risky business. Evolving technology—above all, radar—increased gun efficacy exponentially. David M. Keithly
Chamberlain, Peter, and Terry Gander. Anti-Aircraft Guns of World War II. New York: Arco, 1976; Hogg, Ian V. The Guns of World War Two. London: MacDonald and Jane's, 1976.; Hogg, Ian V. Anti-Aircraft: A History of Air Defense. London: MacDonald and Jane's, 1978.; Werrell, Kenneth P. Archie. Flak, AAA, and SAM. Maxwell Air Force Base, AL: Air University Press, 1988.
David M. Keithly