Warfare is often said to be 'the engine of invention' and it might be supposed that anti-aircraft measures were first developed during the Great War. But not long after Orville and Wilbur Wright proved both the possibility and the practicability of controlled powered flight in their 12 horse-powered aeroplane at Kitty Hawk, North Carolina, USA in 1903, quite a lot of serious thought had been given to the potential threat that aircraft might pose on the battlefield.
In 1909, the German Army demonstrated a converted field gun for anti-aircraft use. These were intended for deployment against aerial reconnaissance, or gun battery spotting aircraft. By 1914 a few had been commissioned and were in service.
The French Army went a bit further and commissioned purpose built anti-aircraft armoured cars carrying the famous 'soixante-quinze' (seventy-five millimetre) M1897 field artillery gun.
At the outbreak of war in August 1914, the British had also produced some tractor mounted anti-aircraft guns using the standard British 3-pounder field artillery piece.
It may be assumed that the mounting of these field guns on mobile platforms was to facilitate the manoeuvrability of the guns around the battlefield. But, in fact, there was also an element of wanting to chase the aircraft as they flew along on their missions. Such was the low speed of the aircraft at the outbreak of the war this was at least a theoretical possibility. As the speed of the aircraft quickly improved during the war, even the potentiality of this idea disappeared, like the over-flying aircraft, into the aether.
Post-August 1914 innovations
Almost as soon as the war on the Western Front began, there was a quite an unanticipated increase in aerial operations, particularly when the fighting became static and trench-bound. Any other sort of battlefield reconnaissance became increasingly difficult and hazardous, so 'directed fire' co-ordinated by aircraft, became a very important factor. This meant that more efficacious and widespread anti-aircraft artillery - AA. (also AAA.) or 'Archie' as it became known - had to be found.
Obviously, the first choice was the modification of the existing artillery guns to enable them to fire in a more vertical orientation, and, as far as possible, to track the aircraft in flight. Indeed, some of these modifications to the existing standard artillery guns were so successful that they remained in use throughout the war. Meanwhile, the race was on for more effective purpose made models.
As seen at the time, the required operational characteristics of these guns were:
- Mobility on the battlefield.
- Light shells with a high range using standard propellants.
- Standard calibre shell to facilitate manufacture and supply.
- Standard mass production design.
- Readily adjustable shell fuses to facilitate height settings.
- Rapid firing rate to facilitate the 'tracking' of the aircraft.
In the event, the British went largely for the British standard 3-pounder guns and suitable modifications and variations were made to it as the war went on. It was left to the Germans in 1918 to come up with the much more successful cannon-shell firing gun. Their rapid firing 20mm cannon proved to be so successful that it became the forerunner of the standard light anti-aircraft guns of the Second World War, and after.
Types of projectiles
In the early days of the war, when the aircraft were of a very light construction and inherently unstable, almost any kind of damage to the airframe could be critical, be it by shrapnel balls or by high explosives (H.E.).
However, it was quickly realised that whilst a hit with shrapnel could have deleterious effect on both the aircraft and the pilot, a hit with a H.E. shell would almost always be very serious indeed.
Accordingly, despite the fact that shrapnel had a much greater chance of a strike, the more certainty of H.E., if and when it did hit, meant that as the war progressed and the planes became much sturdier, the standard shrapnel-ball shell was less and less used against aircraft.
A variation of the shrapnel-ball shell came with the development of the Thermite Shell that was specially developed for use against the highly flammable Zeppelin airships. Ordinary bullets could simply pass through the airship without causing crippling damage. The Thermite Shell produced a flaming shower of incendiary shrapnel that was highly efficient against the Zeppelins. It was also found to be highly effective against other aircraft and became a standard AA. shell by the end of the war.
An inherent problem with firing anti-aircraft shells against an aircraft in flight is the three dimensional problem of the determination of height, direction and the speed in the forward movement of the aircraft. Assuming the problem of estimating the height, direction and speed of the aircraft can be resolved, there still remains the problem of either getting the shell to explode on contact with or, much more feasibly, to explode in close proximity to the target.
In the absence of the 'close proximity fuse' in the Great War, (i.e. fuses that are activated when the target comes within a pre-determined distance) the only solution was a very judicious cutting the length of the shell fuse to give the necessary accuracy. And this method was used throughout the war. So it can be appreciated what a really skilful task anti-aircraft artillery became. Of course, even close 'flak' (as anti-aircraft shelling became known) was a very effective deterrent to enemy aircraft. But, actual 'Kills' required a high degree of skill or luck.
Batteries and maximisation of effect
It was quickly realised that in view of the problems of aircraft height, direction and speed, efficacy could only be achieved if anti-aircraft artillery worked in co-ordinated way with batteries of guns.
The minimum set-up was two guns: one gun to fire ranging shots, whilst the other followed up sufficiently quickly to hit the plane before it flew out of range.
It also quickly became apparent that having a large number of small gun batteries scattered over the battlefield, on the chance than an aircraft would fly by, was highly inefficient. This role of random search for, and interdiction of reconnaissance or spotter aircraft planes, gradually became the province of the specialised 'fighter' aircraft.
However, large concentrations of AA guns became imperative around large vulnerable targets such as ports, airfields, military rear assembly areas and civilian production and residential areas.
Another use of large batteries was to put up 'walls of fire' or 'box protection barrages' to interdict aircraft from a limited area for a limited period - say, during an offensive. To further enhance the effectiveness of these barrages at night, searchlights and flares were also widely used to illuminate any aircraft intruders.
The Barrage Balloon Companies of the Western Front were primarily concerned with their own battlefield observation role. The balloon companies treated enemy aircraft as a threat to the balloons rather than using the balloons themselves as an anti-aircraft defence measure.
As the war progressed, the observation balloons were often grouped and had skeins of wires suspended between them to protect themselves against the aircraft sent to shoot them down. As an off-spin of this tactic, the presence of the connected balloons often have deflected the flight path of the enemy aircraft and made them more vulnerable to the anti-aircraft guns that were increasingly sited close to the balloon sites for their protection.
With the entry of military aircraft in the Great War, anti-aircraft artillery became an essential component of the protection measures on the Western Front.
Due to the lack of proximity fuses, the efficacy of the AA. was, at best variable, and rather unpredictable.
The technical progress in telescope ranging, improvements and refinements in ballistics and new patterns of the deployment of the AA guns, did not really keep up with the galloping development of all kinds of aircraft. Consequently, while the anti-aircraft artillery comprised a fair proportion of the British artillery pieces on the Western Front, which rose to a maximum of 6,000 guns and employed 25% of the troops, the number of kills that could be definitely attributed to anti-aircraft artillery was low. Indeed, ground-fire from small arms - rifles and machine-guns - was much more effective against low flying aircraft. The recent disclosures that the German air-ace Rittmeister Baron Manfred von Richthofen was almost certainly the victim of an unknown Australian rifleman, or machine-gunner, being a good case in point.