Counter-Uncrewed & Low-Altitude Defence

During the American Civil War the Union Army's use of balloons compelled Confederate troops to devise means of combating them, including artillery, rifle fire and sabotage. The attempts were unsuccessful, but they mark the earliest recorded efforts at countering aerial platforms over a battlefield.

During the siege of Paris in the Franco-Prussian War, the French used balloons to communicate out of the city, and Krupp mounted a modified 1-pounder gun on a carriage specifically to shoot them down. This is the earliest known weapon purpose-made for the anti-aircraft role, the ancestor of all ground-based air defence.

By 1910 only Krupp, Erhardt, Vickers Maxim and Schneider had released details of guns for the anti-balloon role, covering calibres from 47 mm to 105 mm, together with proposals for tracer, shrapnel and incendiary ammunition and impact or time fuzing. The French balloon gun of the same year was an 11-pounder on a vehicle mounting. Sights remained simple because balloons were slow, but the problem of faster aeroplanes was already recognised.

Twining's 1-pounder concept was drawn up against the perceived threat of airships. It became the basis for the US Navy's first operational anti-aircraft cannon, the 3-inch/23 calibre gun.

During the Italo-Turkish War, Turkish forces lacking any anti-aircraft weapons brought down an aeroplane with rifle fire. Lieutenant Piero Manzini's machine, shot down on 25 August 1912, was the first aircraft to crash in a war as a result of ground fire.

By 1913 only these two powers had both developed guns able to engage balloons and aircraft and addressed the attendant questions of military organisation. Britain's Royal Navy soon followed with the QF 3-inch and QF 4-inch AA guns alongside Vickers 1-pounder pom-poms.

Reported on 8 July 1914, weeks before war broke out, the plan was to dot the British Isles with towers each mounting two quick-firing guns of special design, with a complete circle around naval installations and other vulnerable points. It is an early statement of homeland air defence as a national undertaking.

By December 1914 the RNVR was manning AA guns and searchlights at some nine ports, while the RGA took responsibility for AA defence in the field with motorised two-gun sections first formed in November 1914. Initial equipment was the QF 1-pounder pom-pom, a 37 mm version of the Maxim gun.

The British height/range finder, beginning with the Barr & Stroud UB2 optical coincidence instrument, and the height/fuse indicator solved the fuse-length problem, while tachymetric devices tackled deflection. The French electrical Brocq system and the British Wilson-Dalby gun director produced vertical and horizontal deflection angles so guns could be aimed at a target's future position. These instruments established fire control as the heart of air defence.

On 30 September 1915 enemy aircraft bombed Kragujevac; Ljutovac fired a modified Turkish cannon captured in 1912 and brought one down, killing both crew. It was the first occasion in military history that a military aircraft was destroyed by artillery fire from the ground.

The 13-pounder QF 6 cwt Mk III of 1915 was followed by 18-pounders lined down to take the 13-pounder shell with a larger cartridge, the more satisfactory 13-pounder QF 9 cwt. Most armies' earlier ad hoc expedients of propping field guns on embankments had proved largely useless without means of measuring range, height or speed.

German air attacks on Britain grew in 1915 and existing AA efforts were deemed ineffective, prompting the appointment of a Royal Navy gunnery expert to improve them. Defences were expanded with 75 mm and 3-inch guns in place of the ineffective pom-poms, and searchlights and acoustic detection were introduced for night attacks. By December 1916 there were 183 AA sections defending Britain.

The gun entered service in 1915 as a refit to USS Texas and was subsequently mounted across many ship types as the need for anti-aircraft protection became recognised. In the Second World War it was the primary armament of destroyer escorts, patrol frigates, submarine chasers and minesweepers.

The naval 3-inch gun was adopted by the army and given a new field mounting in 1916, becoming the standard British heavy AA weapon of the war. Most of the 183 AA sections defending Britain by December 1916 were equipped with it.

Drawing on data gathered by the wartime Anti-Aircraft Experimental Section and extensive post-war analysis, the two-volume text set out five key recommendations for heavy AA equipment: better ballistic shells with mechanical time fuses, automated higher rates of fire, long-base optical height finding, centralised tachymetric fire control, and more accurate sound location. It codified the doctrine of aimed predicted fire that shaped inter-war air defence.

Adopted by Britain in 1925, the predictor took target height and tracking input and produced bearing, quadrant elevation and fuse setting, transmitted electrically to repeater dials at the guns for 'pointer matching'. Similar systems were adopted elsewhere, including the Sperry M3A3 used by Britain as the Predictor AA No 2.

ADGB, established in 1925, is probably the first use of the term 'air defence'. It provided the organisational frame under which British ground-based guns and fighters were later unified.

Formed in 1925, the Corps reported hostile aircraft flying over Britain, supplying the human sensor layer of the national air defence picture. It complemented optical and acoustic detection until radar matured in the late 1930s.

From the early 1930s radar development advanced far enough that by the late 1930s work on acoustic sound locators was generally halted. Initially used for airspace surveillance, radar soon produced gun data: Britain's Radar, Gun Laying, Mark I was in use by 1939 and the German Würzburg entered service in 1940.

In the late 1930s Britain linked radar, observers and the British Army's Anti-Aircraft Command under ADGB in a single command and control network. It made layered air defence a coordinated system rather than a collection of guns, though field-deployed air defence relied on far less sophisticated arrangements.

Ordered by the Swedish Navy in the late 1920s, the light, rapid-firing and reliable 40 mm soon gained a mobile four-wheel carriage. Adopted by some 17 nations just before the Second World War, it became the archetypal short-range air defence gun and remains in limited use today.

Germany had been barred from AA weapons by the Treaty of Versailles, with Krupp designers moving to Bofors and only covert training resuming in the late 1920s. The 8.8 cm FlaK 18 of 1933, followed by the 36 and 37 models, became the backbone of German heavy air defence and proved formidable against armour as well.

Trials in 1935 showed the minimum effective round against low-flying aircraft was an impact-fused 2 lb HE shell, ending reliance on World War I machine guns. In 1936 Britain chose the Bofors 40 mm, licensed for UK production, along with a twin Vickers 2-pounder; the air-cooled Bofors proved vastly superior on land. The Predictor AA No 3, the Kerrison Predictor, was introduced with it.

Preferred since 1928 but delayed six years for funding, the 3.7-inch entered production in 1937 in mobile carriages for the field army and transportable guns for static sites. It became the backbone of British ground-based heavy air defence in the Second World War.

Browning's dual-role automatic 37 mm was standardised in 1927 as the T9 but proved worthless in the ground role; an AA carriage was developed and the weapon entered service in 1939. Prone to jamming, it was eventually replaced in AA units by the Bofors 40 mm.

Drones available in quantity from 1939 allowed realistic testing against flying, manoeuvring targets for the first time, and the results were sobering: high-level manoeuvring drones were virtually immune to shipboard AA, while simulated dive bombing showed the dire need for autocannons. Other powers largely did not test this way, possibly leading them to underestimate the threat and overrate their own systems.

In October 2023 a 40 mm railgun fired 320-gram projectiles at over 2,000 metres per second from a vessel. It is the first demonstration of the technology at sea, relevant to cheap high-volume interception of low-altitude threats.

During the Battle of Mosul dedicated counter-drone systems were fielded against uncrewed aircraft used by ISIL. It marks the operational arrival of counter-UAS as a distinct branch of low-altitude defence against cheap, numerous threats.

The September 2012 Camp Bastion raid illustrates what the article identifies as the most effective insurgent method of countering aircraft: penetrating an airbase perimeter to destroy aircraft individually, or engaging them by indirect fire such as mortars. It frames base defence as part of the counter-air problem.

Started in 2005, the project achieved a world-record 33 MJ muzzle energy in December 2010, launching a 10.4 kg projectile at 2.5 km/s, with planned rates of ten rounds a minute and self-guided projectiles out to 200 nautical miles. Funding was pulled in mid-2021, though projectile development continued for conventional guns, and power requirements remain a limiting factor despite renewed interest for defence against anti-ship ballistic missiles.

In 2004 responsibility for ground-based air defence passed out of Royal Air Force control, ending a long-standing division of the UK's integrated system. It reflects recurring institutional contest over who owns low-altitude defence.

The newest surface-to-air missiles claim the ability to detect and engage stealth targets, the S-400 reportedly detecting a 0.05-square-metre radar cross-section target at 90 km. Such claims shape assessments of which airspaces can be contested.

During the 1993 Battle of Mogadishu rocket-propelled grenades were used against helicopters, a tactic repeated during Operation Anaconda in Afghanistan in March 2002. RPG rounds are fused to detonate automatically at 920 m, which makes them usable in an improvised air defence role.

During the first Gulf War Patriot batteries were deployed with the objective of covering populated areas rather than individual military targets. It demonstrated missile defence as an extension of air defence over civilian populations.

In 1990 Pakistan constituted air defence as an arm of its own, in contrast to the British Army where it remains part of the artillery. The structural choice reflects differing views of air defence's institutional weight.

Argentina deployed 35 mm Oerlikon GDF-002 twin cannon and Roland missiles, while Rapier was the primary British ground-based system alongside a few new FIM-92 Stingers; both sides used Blowpipe. British naval defence layered Sea Dart and Sea Slug with the shorter-range Seacat and new Sea Wolf. The war was an early test of layered missile and gun air defence in combat.

Optical and acoustic sensors of the First World War were superseded by radar, which was in turn supplemented by optoelectronics in the 1980s. Multi-sensor detection became standard in modern air defence.

Man-portable air defence missiles appeared in the 1960s and have since supplanted or replaced even the smallest guns in most advanced armies. Smaller missiles mounted on armoured cars and tank chassis began replacing gun-based SPAAG systems in the 1960s and had displaced almost all of them by the 1990s.

The wartime command, which at its peak comprised three AA corps and 12 AA divisions, was disbanded in March 1955. During the 1960s and 1970s RAF Fighter Command instead operated long-range air defence missiles to protect key areas of the UK.

NADGE linked European national air defences into a single ground environment and later became the NATO Integrated Air Defence System. It extended integrated command and control from the national to the alliance scale.

After years of post-war development, guided missiles matured into viable weapons: the US upgraded its defences with Nike Ajax and the USSR with the SA-2 Guideline, after which the larger anti-aircraft guns disappeared. By 1955 the US deemed the Bofors 40 mm obsolete against jets, having briefly pursued the automated 75 mm Skysweeper. The shift from ballistic guns to guided missiles is the central transition in 20th-century air defence.

Batteries of four 90 mm guns firing radio proximity-fused shells, with targets automatically tracked by gun-laying radar feeding an electronic analogue computer, defended Folkestone-Dover and then Antwerp in the 'Antwerp X' project. In a single week in March 1945 close to 90 per cent of V-1 missiles on track for the Antwerp defence zone were destroyed. It is the first mass defeat of cheap flying munitions by an automated engagement chain.

Two-inch and three-inch unguided rockets developed from 1930s solid-fuel work were fired in large numbers from Z batteries and fitted to warships, being used for barrage fire against low-level and dive bombing attacks. The firing of one during an air raid is suspected to have caused the Bethnal Green disaster in 1943.

Prompted by the Dambusters raid of 1943, the Germans sought a system able to kill any low-flying aircraft with a single hit; a 50 mm proved inaccurate and was replaced by a 55 mm. Search and targeting radar fed a centralised computer that corrected for windage and ballistics and drove hydraulic gun laying, leaving operators only to load and select targets. It was in late development when the war ended.

British imperial-measurement drawings were supplied to the Americans, who copied the 40 mm unlicensed before moving to licensed production in mid-1941, with the design reworked for mass production. The Oerlikon 20 mm was adopted in exchange for M2 machine guns and by the end of 1942 accounted for 42 per cent of all aircraft destroyed by US Navy shipboard AA.

Created in 1941, the Regiment took responsibility for defending airfields against air attack, eventually equipped mainly with Bofors 40 mm guns. It established the principle of dedicated ground troops protecting air bases.

The Strategic Air Defence Service was created in 1941 to defend the homeland and became an independent service in 1954, alongside PVO SV covering the ground forces. The split institutionalised air defence as a separate arm of a national military.

Of 1940 origin, the quad-20 mm autocannon mount became one of the most widely seen German air defence weapons on both land and sea. The American Maxson M45 Quadmount of four .50 calibre machine guns, often carried on a half-track as the M16 Multiple Gun Motor Carriage, was a direct answer to it.

QF 3.7-inch guns formed the backbone of ground-based defences, with Anti-Aircraft Command under the operational command of RAF Fighter Command growing to 12 AA divisions in three AA corps at its 1941–42 peak. Fixed HAA and LAA defences were also established at Malta, the Suez Canal and Singapore.

Work begun on a 105 mm static mounting in 1924 was overtaken by the 90 mm, designed with mobile carriages and static mountings able to engage air, sea and ground targets. Approved in 1940, it became the standard US heavy AA gun and, like the German 88, an excellent anti-tank weapon.

German wartime rocket research was the most advanced of the war, yielding the unguided Fliegerfaust shoulder launcher, described as the first man-portable air defence system, and radio, wire and radar-guided missiles such as Wasserfall. Severe war conditions limited all of them to small numbers used mainly by training or trial units, but they defined the post-war direction of air defence.