An Effective Air Defence System
It was quickly recognised a century ago that the basic requirement for effective air defence was a system comprising several constituent parts. The first, the observation element, identified and located the enemy aircraft, while the second, an efficient communications system, sent the information as rapidly as possible to an air defence operations centre. At the operations centre, the information could be displayed in an understandable form quickly enough to enable the air defence commander to react accordingly by alerting anti-aircraft gun batteries and despatching fighter aircraft to intercept and shoot the enemy down. All parts of the system, identification and location, dissemination and display, command and control, fighter interception or anti-aircraft fire control, had to function efficiently and in concert to achieve the desired end result – the destruction of the enemy.
The system developed in the First World War involved observation by military observers (some using concrete “acoustic mirrors” for sound detection of aircraft), police and railway officials. Curious as this latter arrangement might appear, it was in fact a sensible and imaginative innovation. The railway network at the time was an important strategic asset to the country and also boasted station masters and dense patchwork of stations extending across large parts of the country. Justas important, these were linked together by telephone and telegraph, which provided that most vital component – rapid communication.
Operations Rooms with map tables and other communications equipment were established in London, one being located at Liverpool Street Station. Eventually, a central control room was set up in Horse Guards and twenty-five sub-controls around the country passed details of “plots” on raiders. There were ten “plotters” seated at the map table, each with a headset connecting him to several sub-controls. Colour-coded counters with arrows were placed on the map tables to depict the tracks of hostile aircraft and airships and there were indicators to show where bombs had been dropped. The colours on the counter corresponded to five-minute coloured segments on the operations room clock, which thus indicated how old the “plot” was. “Stale” plots more than ten minutes old were removed from the table. The air defence commander, General EB Ashmore, sat in a raised gallery giving him an unobstructed view of the map table and could talk directly to any sub-control.
Ashmore and his team had thus more or less solved the organisational problems associated with air defence by the end of the War. The foundations of the later air defence system, which came to be known as the Dowding System, had their origins in Ashmore’s organisation, known as the London Air Defence Area [LADA]. The technological issues that LADA faced were less easily addressed. The acoustic mirrors were not particularly successful, and the limited results of enemy air attacks owed as much to the technical shortcomings of German aircraft as to the rapid improvement of UK air defences. However, the acoustic mirrors were the focus for some of the earliest attempts at co-operation between scientists and the military in the air defence field. This relationship, although not without its difficulties, would bear far more significant fruit in a later conflict.
In the 1920s, as now, defence spending came under intense pressure. However, this did not mean that UK air defences were entirely neglected. Under the Treaty of Versailles, Germany was forbidden military aircraft, leaving Franceas the only major power theoretically capable of threatening the From the air. The 1920s air defence system was therefore designed to address that potential, if unlikely, eventuality. A number of committees investigated various aspects of the air defence problem and produced recommendations for a new approach, drawing on the experience of the LADA and creating separate zones for anti-aircraft guns and fighters (to avoid friendly fire incidents). The Aircraft Fighting Zone originally extended from Duxford, near Cambridge(now part of the Imperial War Museum),to Devizes in Wiltshire. The outer edge of this Zone was about 35 miles inland from the coast, a distance dictated by the amount of warning expected of an incoming raid combined with the time it took the contemporary biplane fighters to climb up to 14,000 feet – the height at which it was anticipated that the bombers would fly.
There was an Outer Artillery Zone in front of the Aircraft Fighting Zone, and an Inner Artillery Zone behind it, mainly covering London. The Aircraft Fighting Zone was sub-divided into ten Sectors, each with a front of about fifteen miles. The four Sectors to the south and east of London were to be defended by two fighter squadrons, and the others would have one squadron. A further three squadrons would be stationed near the coast to intercept and harass the incoming raids as early as possible. Observer posts were to be established across southern England linked to Observer centres and those on the coast were to be equipped with acoustic mirrors. In October 1925, an Observer Corps [later the Royal Observer Corps] was established, utilising volunteer civilians to man the observer posts.
In the 1930s, following Hitler’s rise to power in Germany and the establishment of the Luftwaffe, the air defence system was progressively re-oriented from south to east and extended to cover the whole country. Of course, it was anticipated that France would be allied with Britain in the event of war and that the threat from Germany would come from across the North Sea. However, the rapid development of aviation during the 1920s and 1930s served to complicate the issue. The German Gotha biplane bombers of 1917 had flown at a stately 70 mph but, by the 1930s,their sleek monoplane Dornier and Heinkel descendants could reach nearly 200mph. With enemy bombers flying at such speeds, there would be less time to mobilise the air defence system against them.
Photo: Major General Edward Bailey Ashmore qualified as a pilot On September 3 1912. In 1917, having commanded 4th Brigade, RFC during the Battle of the Somme (1916), he was appointed to set up an air defence system for London, establishing a balloon barrage and a gun belt 25 miles to the east of the capital, with fighters patrolling inside it. White arrows on the ground directed the fighters to incoming enemy aircraft. Ground observers were used as well as wireless-equipped tracker aircraft.
RAF Museum. © UK MOD Crown Copyright 2015.