Radar, the Wizard War
Radar, standing for radio detection and ranging, relies on the fact that most kinds of 'targets' reflect radio signals, producing so-called 'radar echoes'. In order to detect these echoes we must first generate radio signals or waves. Generating these signals was made possible by the invention of the thermionic valve by the American engineer, Lee de Forest in 1906.
A second requirement was an instrument that could measure the time between the transmission and return of reflected high frequency pulses, from which could be calculated the target's distance from the observation point. This requirement was fulfilled by the oscilloscope, which displayed the waveform and timing of electrical signals on a cathode ray tube not unlike a television screen. Similar instruments are used in hospitals for measuring heartbeats and pulses.
Oscilloscopes became available in the early 1920s when serious consideration began to be given to the possibility of determining distance by radio.
Thus the thermionic valve, the oscilloscope and the cathode ray tube became components of radar equipment able, firstly, to project radio waves against an object and receive an echo and, secondly, able to measure the time taken by the echo to travel from the reflected object to an observer who is watching it.
It was, however, in Britain that the first operational radar system for providing early warning of hostile aircraft was developed.
In 1932, faced with the possibility of rearmament in Germany and recalling the attacks by bombers and airships in the First World War, Prime Minister Stanley Baldwin, made the alarming declaration that 'the bomber will always get through'. His fears reflected the reality of Britain's system for early warning which, at that time, depended on an unreliable system of sound locators, the most sophisticated of which were pointing, not across the North Sea, but in the direction of France.
In this climate H.E. Wimperis, Director of Scientific Research at the Air Ministry, wrote to R.A. Watson-Watt, head of the Radio Research Laboratory of the National Physical Laboratory, and asked if it would be possible to direct sufficient energy in electromagnetic waves to form a 'death ray'.
At the time, this did not appear to be an unreasonable or far fetched question. The possibility of disabling vehicles or aircraft in this way had been circulating in science fiction writing and the popular press for some years. Watson-Watt's assistant, A.F. Wilkins, quickly calculated that a death ray was impractical but his figures also suggested that reflections of radio pulses from aircraft might be detectable. On 26 February 1935, Watson-Watt and Wilkins used a receiver installed in a caravan to detect signals at a range of eight miles (thirteen kilometers) from a metal-clad bomber flying up and down the short wave beam of the BBC's Empire Radio Station, built by Marconi, at Daventry in the Midlands. This was the first successful ground to air test involving radio detection.
The previous month, quite independently, Marconi had asked the company's factory in Genoa to build him a small transmitter of 50-centimetre wavelength, with a receiver to match. In April, while testing them at Torre Chiaruccia outside Rome, he bounced radio waves off his car, driven back and forth by his chauffeur, and then off a circling aircraft. Although the Italian military authorities were made aware of this development, they failed to realise the great potential of radiolocation.
The Chain Home Network
May 1940, Germany crushed French forces conquering the country in a matter of weeks. Hitler rode triumphantly into Paris, he was on the verge of completing his lightning conquest of Europe. Only Britain protected by its age-old natural barrier the English Channel stood in his way. Defying the odds Britain refused to surrender.
Summer 1940, the Nazi Blitzkrieg swept across Europe. Countries from Poland to France fell before the German war machine. Britain was on the verge of collapse. In Liverpool a loan physicist smuggled a trunk across the Atlantic to the United States. That case contained Britains greatest military secret.
Britain was under constant air attack the purpose of which was to knock-out the Royal Air Force as a prelude to invasion of the British Isles & Hitler knew he had the military strength to invade Britain but had to establish air superiority first. The Luftwaffe had 2,400 planes; four times that of the RAF. Once Hitler captured Britain his hold on the continent would be secure. Even the United States might not be able to challenge his domination. The fate of Europe hung in the balance. One hope for British survival was the new & top-secret technology of Radar.
Radar was more discovered than invented. By the 1930s radio waves were everywhere, conveying entertainment and information to millions. In the course of transmission radio technicians noticed that large objects reflected their signals. The phenomenon was dubbed radar for Radio Detecting & Ranging. The word radar is spelt the same forward or backward reflecting the process it describes. When the radar antenna sends out its pulses they bounce back from the unknown target & the result is seen as a peek on the radar screen. Reading this pattern the distance & speed of an approaching plane are charted.
Britain and the United States saw radar as one of many technologies worth pursuing. Britains leaders faced with Hitlers threats gave air defence top priority. Their radar pioneers worked from a remote gothic mansion, Bawdsey Manor, on the Suffolk coast 90 miles (145 km) from London. They developed a national radar system, The Chain Home Network. By 1940 the eastern coastline of Britain was ringed with twenty-one radar towers. These electronic sentries provided early warning of enemy attacks from up to 100 miles (161 km) away. Hitler and his generals had built the most awesome fighting machine ever but they were unprepared for this new technology. Radar was entirely unanticipated and when the strategists of air power developed their ideas in the 1920s & 30s what they imagined was free access to aerial attack on the enemys homeland. Radar had not been accounted for.
Herman Göring chief of the Luftwaffe suspected that the huge towers bordering Britain were a radar network. A zeppelin was dispatched to search for radio waves. It detected none possibly because of scanning the wrong wavelengths. The Germans compounded their intelligence failure by a tactical error. With the swift fall of France German leaders seemed to believe their own propaganda of Nazi invincibility. The German forces in France gave themselves a holiday. They were in France with wonderful summer weather, good food, excellent wine, beautiful women & that cost them dear because it gave the British an extra few weeks to prepare for the inevitable onslaught.
The Chain Home Radars reached across the English Channel detecting enemy aircraft as they massed in attack formations over French airfields. Data on the location and speed of the Luftwaffe squadrons went to underground operation centres, where giant maps of the coastline were marked to reflect the current situation. Generals relayed their orders to four RAF command centres where fighter planes were scrambled to intercept. In World War I airborne planes were on their own but now RAF ground centres maintained control over their squadrons using radar to direct them on intercept courses. Only when enemy planes were spotted would command pass to the pilots.
Radars early warning would allow the RAF to conserve its limited resources of planes, fuel & pilots & by surprising the enemy at the right place with the right number of aircraft they downed two Luftwaffe planes for every RAF one lost. As the Battle of Britain stretched over the summer of 1940 radar denied Hitler what he needed to launch an invasion. For the first time the Nazi blitzkrieg had been slow, proof that Germany was vulnerable which gave British civilians the courage to withstand the constant bombardment. Radar had kept Britain alive but time was running out. Even with a hit ratio of two to one the Royal Air Force would soon succumb to the far greater resources of the Luftwaffe. Constant daily raids of British airfields by the Luftwaffe were taking their toll & for Hitler complete victory was in sight but his ignorance of radar & a tactical blunder would sabotage his dreams.
In August 1940 Churchill ordered the first attacks on German territory. Although the strikes caused little damage in Berlin they enraged Hitler. Already furious with British resistance he ordered massive aerial attacks on London. Instead of concentrating on knocking-out British radar stations, aircraft & airfields the Luftwaffe was ordered to carry out retaliatory raids against London & the civilian population, which was a waste of German strategic airpower. Had Hitler not made this tactical blunder the RAF would not have been able to prevail. The summer long struggle culminated in an epic air battle on 15th September 1940. By late in the day the Luftwaffe had lost 60 aircraft to the Royal Air Forces 26. Unknown to the Germans the British had exhausted their reserves of fighter planes. Britain was defenceless. Of this day Churchill later wrote, The odds were great, our margins small, the stakes infinite. Germany, counting its own losses finally decided to call off further attacks. Two days later Hitler cancelled his invasion plans of the British Isles. Guarded by newfound technology & old-fashioned tenacity Britain had survived its darkest hour.
Hands across the Sea
Even as the Battle of Britain raged British scientist turned their thoughts to long-term survival. Faced with few options they decided to share their most vital military secrets with the United States. America possessed the scientific & industrial capacity to support a long war. Radar pioneer Taffy Bowen collected his countrys scientific bounty in a single black box & carried it on the Underground to the Ministry of Supply & from there by taxi to a hotel. The box was to large to fit in the hotels safe deposit box so he slept with Britains most precious secret wedged under his bed! Of all the blue prints, diagrams & devices in Bowens trunk none mattered more than a small radio transmitter called the Cavity Magnetron. Existing radars transmitted at low frequency or long wavelengths with each radio wave measuring one (3.28 feet) to ten (33 feet) metres. The Cavity Magnetron could generate shorter or microwaves only 10 centimetres long (4 inches). Microwaves produced a narrower beam, much more accurate in pinpointing a targets location. While previous systems required large transmitters microwaves offered the promise of sophisticated radars compact enough to fit on a plane. The prospect of airborne radar took on added urgency when Hitler switched to night raids on English cities. Thousands took to sleeping in the Underground. On a single October night London was bombed for nine straight hours leaving hundreds dead.
Aboard the Canadian Liner Duchess of Richmond Taffy Bowen carried the precious Cavity Magnetron to the United States. Americas first radar research centre was hastily established on the M.I.T. campus in Cambridge, Massachusetts and named the Radiation Laboratory or Rad Lab. Americas top physicists were recruited in secret to this project more than a year before the United States entered the war. Among them were ten future Nobel laureates, several university presidents, two science advisers to presidents- the best of the best were involved in this secret project often with nothing more than someone they knew telling them to come to Cambridge or Boston to do secret war work. American scientists were new to war work & untutored in the ways of secrecy for example at that time there was no distinction between internal or external calls at the Rad Lab! The Nazis apparently never took advantage of the lax security but by late 1940 they had belatedly realised radars importance and sent their best scientific minds to match allied technology but an unprecedented series of partnerships would keep the Rad Lab a step ahead. Physicists accustomed to working alone joined in teams to develop ideas. Civilian & military leaders who had clashed in World War One co-operated freely. American physicists delighted in collaborating with their English cousins.
The Rad Lab expanded with astonishing speed; by the end of the war over 4000 people were involved. Building after building was turned over to the lab, strange domes appeared on M.I.T. rooftops. Experimental radars bounced test signals off the Boston skyline. Despite this effort developing airborne radar for use took time. In Britain the Luftwaffes rein of terror continued unabated to into 1941. Frustrated in his attempt to crush British resolve in June 1941 Hitler launched a surprise invasion of Russia. At the Rad Lab scientist turned their attention to developing ground to air radar for hunting ships & submarines. Soon no vessel would escape radar. With the United States still officially at peace its naval officers were slow to realise radars importance. All that would change on 7th December 1941. At 7 in the morning local time radar sites at Pearl Harbour detected a massive incoming airborne force. The information was passed up the chain of command where it was promptly ignored. This strange new gadget called radar it was decided must be malfunctioning. At dawn the Japanese struck. The assault on Pearl Harbour left approximately 2,400 dead, 300 planes destroyed and the entire U.S. Pacific Fleet in chaos. Never again would radars early warning power be ignored.
The war had become truly global. Allied leaders agreed that their top priority was maintaining supply lines to Britain. If Hitler starved Britain into submission there would be no base from which to liberate Europe. The demands of war drove radar research at a fantastic pace compressing decades of basic advances into just five years. At the Rad Lab physicists knew that only constant innovation would keep them ahead. One of the toughest challenges was directing planes to targets thousands of miles away. In 1943 the allies began massive air strikes inside Germany where the skies were cloudy 3 out of 5 days particularly in winter reducing the bombers visibility. Dr. George Valley experimented with converting anti sub-radars into directional beacons. His new system was called the H2X.
The H2X though only accurate to within a few hundred yards got the job done. It allowed bombing through clouds & darkness overcoming Germanys natural defences. The H2X was installed in a select group of B-17s that acted as aerial pathfinders. One radar-equipped aircraft would lead up to 750 Flying Fortress on bombing raids. When the leader dropped his bombs the rest followed suit leaving a swathe of destruction larger than a square mile (3 sq kilometres). There was a complete reversal of fortune where pilots who once feared taking off in bad weather where now afforded a degree of protection. They could still find their targets because radio waves penetrate cloud cover where visible light cannot. Now able to fly in all conditions allied planes doubled their sorties ravaging Germany. Just as the war created unleashed weapons unthinkable when it began it revolutionised the concept of acceptable military tactics. The advent of aerial bombing lead directly to the intentional destruction of civilian populations-a policy the allies insisted they would never sink to. The Royal Air force under Arthur (Bomber) Harris actually pursued a policy called de-housing. De-housing was the use of strategic bombing to eliminate the housing of the industrial workers. By dislocating the workers it was hoped this would interfere with the industrial productivity & war fighting capability of the German state but this was a euphemism for attacking civilians.
Germanys use of its radar against the invading allied planes at the beginning of the war was very successful but by 1943 to counter ground to air radar allied aircraft dropped bundles of aluminium strips known as chaff. When these strips were dropped in front of a radar image they scattered the image and sent back a false image so attacking aircraft would use these as a counter measure against an enemys defensive radar. This was enormously effective.
After the war is over Im going to buy myself a British radio set as a token of my regard for their high frequency work. Reichsmarschall Hermann Göring.
By pounding German cities American bombers drew the Luftwaffe into the skies in self-defence, this lead to the destruction of German airpower paving the way for the liberation of the continent. D Day was met by almost no German aircraft. Had the Luftwaffe been in tact on D Day the Normandy landings might have failed. The D Day invasion of France became the culmination of an elaborate electronic chess match. During the Battle of Britain defensive radar had allowed Britain to manage its limited resources. Now Germany was in the same position hoping that radar would protect its frontiers from a vastly more powerful foe. The Nazis only chance to repel the assault was to concentrate their defences. Hitler & his generals would have to guess where the invasion force would land. Tired of losing the radar war Germany had assembled six hundred radars at two hundred sites along the coast from Denmark to Spain. Allied airmen embarked on a series of low altitude high-risk missions to bomb the radars. All but a few were destroyed and those still operational were intentionally left in tact to see what the allies wanted them to see. In the pre-dawn darkness of 6th of June 1944 twelve hundred combat vessels and four thousand landing craft converged on the beaches of Normandy. Meanwhile two phantom invasion forces headed north of the Seine river code named Glimmer & Taxable these small groups of ships carried a series of nine-foot (3 meters) radar reflecting dishes each dish mimicking the echo of a ten thousand tonne ship. Above the phoney fleets planes dropped barrels of chaff as if supporting an actual invasion. They flew in giant rectangular patterns 4 x 16 miles (6.4 x 26 km) and proceeded east giving the illusion of the size & speed of a giant sea borne force. The deception worked. Glimmer caused a full-scale alert in Dunkerque detaining German troops there. By the time the invasion force landed at Normandy the Nazis were so confused they thought this was another decoy. Not until the afternoon of the 6th did they commit their full defences to Normandy. By then it was too late. Before nightfall one hundred and fifty thousand allied troops had landed and secured the beachheads. Within a year of D-Day Hitler would be dead, his Third Reich in ruins. In Boston & Cambridge, Massachusetts the men & women who had done so much to defeat Hitler faced the end of the Rad Lab with mixed emotions. By the end of the war the Rad Lab had designed one hundred and twenty two different radar systems. America had manufactured over one million sets. With the dropping of the first atomic bomb public attention turned to Los Alamos but insiders knew the truth. There was a favourite Rad Lab saying, The atomic bomb ended the war, radar won it.
Even in the darkest days of World War II Americans never faced the treat of attacks on their homes & families. In 1949 that sense of security would vanish forever. August 1949, American sensors detected unusual amounts of radioactive dust in the atmosphere. Analysis confirmed that Russia had exploded its first nuclear device. For many in the free world the thought of Stalin with The Bomb posed a more terrifying threat then Hitler. The Atlantic & Pacific Oceans no longer shielded America from foreign attack. Other international upheavals quickly followed. On the 1st of October 1949 Mao Tse Tung proclaimed the peoples republic of China. The following year the United States & Russia faced off through their client states in South and North Korea. In December 1950 President Truman responded to Chinese involvement in the war by declaring a national emergency.
Radar & the Cold War
In the days before Satellites radar offered the only hope of early detection of enemy bombs. Called Sage (Semi Automatic Ground Environment) the new defence network sought to link massive amounts of information from radar rays spanning the continent. Sage depended on digital computers doing real time calculations allowing information to be collected, collated, analysed and presented at command headquarters in a matter of seconds. Sage was a multi-billion dollar research and development effort to create the first truly national scale network to computerised information gathering and manipulation system. In many ways it is the first model for the Internet. Just as in World War II the ever-changing dynamics of the cold war propelled radar to even greater heights of sophistication. When the Russian launched Sputnik ushered in the Satellite age in 1957 radars began scanning Satellites for their military potential- a process that continues. Modern radars have become very adept at scanning an unknown satellite and determining its shape and its function. The details of how this is done are classified but radar can now produce an image of that satellite. If you had a Volkswagen and a Toyota in orbit modern radar technology could probably tell which was which.
Beginning in the 1960s Intercontinental Ballistic Missiles offered radar a new challenge. An ICBM may carry many warheads each one either a decoy or a live nuclear weapon. It costs an enormous amount of money to fire a 1000 to 1500 pound warhead intercontinental distances. The enemy puts most of his money into the warhead neglecting other items. With modern radar its a matter of reaching out across large distances with an electromagnetic beam and scanning an object to determine its function or functions and capabilities.
In the last sixty years radar has come a long way from accidental echos off passing ships to reflecting the wake of an earthbound ballistic missile, sixty years as a pivotal tool in war & peace. Without radar Hitler might have defeated Britain and with the loss of that last outpost in Europe history might have been very different.