Preventing the enemy from seizing command of or penetrating vital airspace, has always posed problems for war planners. Modern fighter aircraft evolved from those early WW1 machines sent up to dissuade enemy observation aircraft from photographing troop positions, their armament evolving from pistols to machine guns, then eventually multiple guns synchronized to fire through the propeller disk. With the advent of the strategic bomber the fighter's role became even more vital, eventually leading to such classic air defense campaigns as the Battle of Britain. Here fighters played a vital role in preventing the Luftwaffe gaining air superiority over Britain. If the Luftwaffe had achieved Reichmarschall Goerring's boast of "sweeping the RAF from the sky in a few weeks", the way would have been clear for Operation Lion - Hitler's invasion of Britain - to proceed.

Without air superiority, Hitler knew that the cross channel invasion force would have severely mauled by both the RAF and the Royal Navy. Even if they'd managed to land on British soil, without air superiority, he knew from his experiences in the invasion of Poland and France where the Luftwaffe played a vital role in the Blitzkrieg tactics, that his forces would face a tough battle to gain a beachhead and an even tougher battle to break out and capture targets of strategic importance. (see also the author's article on Close Air Support)

In the Battle of Britain, the fighter plane was the key weapon. Statistics on how many aircraft were destroyed by either side vary, however, the kill ratio of fighter vs fighter appears to have been around one to one. Whilst this might not appear to be a war winning ratio in the RAF's favor, it was sufficient to convince the Luftwaffe that they hadn't achieved air superiority as the British aircraft industry was still relatively intact and replacing machines as fast as they were shot down. (Unfortunately this can't be said for experienced pilots, however many pilots who were shot down were rescued to fight again)

Another essential factor in the success of Britain's defense in this battle, one which the Lufftwaffe at first failed to fully appreciate, was the extensive radar network deployed along Britain's coast. Linked to command centers and supported by the Observer Corps, it enabled RAF squadrons to be deployed more effectively - often being able to be in the right place at the right time, at higher altitude which enabled them to break up the bomber formations and inflict maximum casualties. This radar network would now be termed in modern military parlance a "force multiplier" as it allowed inferior RAF numbers to tackle superior Luftwaffe numbers, by giving them the tactical advantage of position, height and surprise.

After the Battle of Britain, although England remained under regular bombing attack by the Luftwaffe it never again faced an air assault of such magnitude - at least not one with the intention of achieving air superiority. By early 1944, however, Britain's air defenses were again put to the test.

The invention of the first operational cruise missile, the German V-1 Buzz Bomb, in many ways posed even greater problems than the Battle of Britain. Here was a cheap, quick to build weapon that was hard to catch and even harder to shoot down, requiring a total rethink of the island's air defenses. Certainly fighter aircraft were an essential part of the defense equation, however something more was needed to combat this tiny explosive packed robot. Guided missiles were in their infancy, with the first workable systems being at least five to ten years distant. Anti-aircraft artillery had proved that given the right circumstances (adequate warning, correct target data etc) it could be very effective.

Possibly one of the greatest technical advances of World War Two, and probably one of the least known, the proximity fuse was by any measure a remarkable achievement. The concept was based on a simple premise - approximately 99% of all artillery shells fired at aircraft missed their target completely, however a significant proportion of these were "near" misses, ie they passed close enough to the target to cause fragment damage if they exploded. What was needed was some way of detecting an aircraft's presence and detonating the shell. For high flying aircraft, part of the answer was using predicted fire, which directed shells into an area calculated the aircraft would soon occupy. A fuse set on the ground using data calculated from the predictors exploded the shell at a predetermined time after firing.

Although this increased the effectiveness of AA fire by theoreticaly creating a barrier of steel fragments through which the aircraft had to fly (if the calculations by the predictor were accurate) often slight errors in calculations, or changes in altitude by the aircraft, meant the "barrier" often exploded at an altitude or position other than that of the aircraft. If shells could be made to detect the proximity of nearby aircraft and then detonate, the chances of scoring a kill would be greatly increased.

Since the 1930s scientists in England and the USA had worked on the idea of a proximity fuze, however the technology wasn't available. One concept tried with only moderate success was using a series of photocells mounted in a shell's nose to detect the shadow or changes in light from an aircraft as the shell approached an aircraft. This was found to work only under very favorable circumstances - usually when the target was between the shell and the sun, a position which required the co-operation of the enemy. It was also found that these photo-fuzes detonated in cloud, so with the concept proven in principle, but being impractical to apply, the photo cell idea was dropped.

What was needed was radar detection - a tall order at a time when radar was in its infancy and a typical installation filled several large rooms, plus it needed enough electrical power to run about 200 homes. Cramming all this inside a space that was less than a housebrick and having it survive the shock of firing seemed impossible. Yet in the space of two years it was done. Development commenced in the USA by the Crosley Radio Corporation in late 1941, and by early 1943, the first models were being tested in action against the Japanese.

The proximity fuze was essentially a miniature radar transmitter and receiver, built into the fuze section of an artillery shell. Using vacuum tubes, (actually a single tube containing several vacuum tubes) this device was activated by the g-forces of the gun being fired - around 20,000Gs for a fraction of a second. On firing, the G-forces ruptured a phial of acid, which was then distributed through the surrounding plates of the battery by the spinning of the shell caused by the barrel rifling. Current immediately flowed to the electronic components and the transmitter began radiating signals. A mechanical safety device, (essentially a clockwork revolutions counter which moved aside a sliding plate which closed a circuit to the explosive) prevented the fuze from arming itself until the shell had travelled a fixed distance from the gun, usually around 3-5000 meters depending on the design, or on some models a setting made prior to firing. Once this distance was passed, the fuze was fully active and when it approached close enough to an object to receive a reflected radar signal of a certain intensity, it detonated the shell.

The first recorded hit against aircraft was reported by the cruiser USS Chicago, when it was attacked by three low flying "Betty" bombers. The ship's aft battery of five inch guns engaged the approaching aircraft, the shells exploding among the formation, knocking down one and damaging the others, which promptly broke off the attack. Other successes were soon reported and the US Navy requested immediate priority for the production and development of fuzes for other calibre weapons.

In Britain, anti-aircraft defences were being prepared for the expected onslaught of the V-1 Flying Bomb (also known as the Buzz Bomb due to the sound of its pulse jet engine). The existence of the weapon had been gleaned by aerial recon in early 1943. Knowing the V-1 was coming, and observing the results already being obtained by the US Navy with early fuzes, the British sent a development team to the USA, to help adapt the fuze to their existing AA weapons - primarily the 3.7inch gun (similar in may ways to the German 88mm) This meant considerable redesign and further miniaturisation of the fuze to adapt it to the smaller calibre weapon, however by early 1944, the first fuzes were being shipped to Britain.

The British had expanded their AA units to cope with the V1 - creating a huge network of guns linked by phone, radio and with mobile radar stations spread along the channel coast. The first line of defence were fighters - which soon found that catching the tiny jet powered missile was no easy task. Flying at over 400mph at around 2000ft, the Buzz Bomb's speed was about equivalent to that of the fastest propellor driven fighters of the day. Those fighters which did close on the missile, soon learned that shooting it down involved considerable risk - the Buzz Bomb had a warhead which contained around 2000lbs of high explosive, which when it exploded would often destroy the attacking aircraft before it could take evasive action. Many fighters were lost this way and many others suffered severe damage from flying through the exploding fireball.

At first the British concentrated their AA gun defences around major cities such as London, however within a few weeks they decided it would be more effective if they moved the entire network to the coast. This was done in a remarkably short time and was a significant achievement involving the transporting of thousands of guns, their ammunition, crews, accomodation, plus the huge task of laying thousands of kilometres of communications cables to interconnect the system with their radars, command centres and observer crews. The move was worth the effort. With uncluttered observation areas for both visual sighting and mobile gun radar, clearer lines of fire out to sea, target detection and engagement became deadly efficient. Those V-1s that did manage to slip thought the first line of fighter defences were met by some of the most concentrated and accurate fire of the war. A key element in the success of these defenses was the proximity fuze - anti aircraft artillery accounting for more than fifty percent of V-1s destroyed. By August 1944, at the peak of the V-1 assualt, less than 10 percent of missiles launched were getting through the combined fighter-AA gun defences. In all from the start off the offensive on 13 June 1944, more than 8500 V-1s were launched at targets in Britain.The proximity fuze accounted for the greater proportion of those destroyed by the defenses.

Eventually special tactics were devised by the fighters to deal with the V1 - some of these included formating on the robot missile and slipping a wing under the V1's wing thereby distrupting the airflow, causing it to roll and dive into the ground (or sea). This proved marginally less hazardous than shooting it down. The first jet fighters to enter Allied service - Gloster's Meteor - were also used to catch the elusive V1, their superior speed enabling it to close on the V1 relatively easily - however the problem of destroying it without self destructing in the process, remained. It was quickly realised that in future conflicts the gun equiped fighter would need extra "reach" to deal with weapons of this nature.

Fortunately the Germans never developed a proximity fuze, although experiments were being carried out towards the end of the war to duplicate the US invention. Instead the Wermacht placed their hopes on the development of guided missiles, several designs being placed in production. These showed potential, however there were too few and their guidance technology needed further development to make them effective.

The modern proximity fuze now has the benifit of solid state technology which gives it increased flexibility - including programmable and in-flight up-date functions. Now fitted to most ground to air and air to air missiles, their principle of operation remains almost the same - which has lead to some interesting and cunning developments in electronic countermeasures.

Recommended reading. History of the Second World War by Sir Winston Churchill.