Tag: radar

RADAR winning the Battle of Britain

Plaque commemorating the Birth of RADAR
Image Kintak, CC BY-SA 3.0 via Wikimedia Commons

The traditional story of how World War II was won is that of inspiring leaders, brilliant generals and plucky Brits with “Blitz Spirit”. In reality it is usually better technology that wins wars. Once that meant better weapons, but in World War II, mathematicians and computer scientists were instrumental in winning the war by cracking the German codes using both maths and machines. It is easy to be a brilliant general when you know the other sides plans in advance!. Less celebrated but just as important, weathermen and electronic engineers were also instrumental in winning World War II, and especially, the Battle of Britain, with the invention of RADAR. It is much easier to win an air battle when you know exactly where the opposition’s planes. It was down largely to meteorologist and electronic engineer, Robert Watson-Watt and his assistant Arnold Wilkins. Their story is told in the wonderful, but under-rated, film Castles in the Sky, starring Eddie Izzard.

****SPOILER ALERT****

In the 1930s, Nazi Germany looked like an ever increasing threat as it ramped up it’s militarisation, building a vast army and air force. Britain was way behind in the size of its air force. Should Germany decide to bomb Britain into submission it would be a totally one-sided battle. SOmething needed to be done.

A hopeful plan was hatched in the mid 1930s to build a death ray to zap pilots in attacking planes. One of the engineers asked to look into the idea was Robert Watson-Watt. He worked for the met office. He was an expert in the practical use of radio waves. He had pioneered the idea of tracking thunderstorms using the radio emissions from lightening as a warning system for planes, developing the idea as early as 1915. This ultimately led to the invention of “Huff-Duff”, shorthand for High Frequency Direction Finding, where radio sources could be accurately tracked from the signals they emitted. That system helped Britain win the U-Boat war, in the North Atlantic, as it allowed anti-submarine ships to detect and track U-Boats when they surfaced to use their radio. As a result Huff-Duff helped sink a quarter of the U-Boats that were attacked. That in itself was vital for Britain to survive the siege that the U-Boats were enforcing sinking convoys of supplies from the US.

However, by the 1930s Watson-Watt was working on other applications based on his understanding of radio. His assistant, Arnold Wilkins, quickly proved that the death ray idea would never work, but pointed out that planes seemed to affect radio waves. Together they instead came up with the idea of creating a radio detection system for planes. Many others had played with similar ideas, including German engineers, but no one had made a working system.

Because the French coast was only 20 minutes flying time away the only way to defend against German bombers would be to have planes patrolling the skies constantly. But that required vastly more planes than Britain could possibly build. If planes could be detected from sufficiently far away, then Spitfires could instead be scrambled to intercept them only when needed. That was the plan, but could it be made to work, when so little progress had been made by others?

Watson-Watt and Wilkins set to work making a prototype which they successfully demonstrated could detect a plane in the air (if only when it was close by). It was enough to get them money and a team to keep working on the idea. Watson-Watt followed a maxim of “Give them the third best to go on with; the second best comes too late, the best never comes”. With his radar system he did not come up with a perfect system, but with something that was good enough. His team just used off-the shelf components rather than designing better ones specifically for the job. Also, once they got something that worked they put it into action. Unlike later, better systems their original radar system didn’t involve sweeping radar signals that bounced off a plane when the sweep pointed at it, but a radio signal blasted in all directions. The position of the plane was determined by a direction finding system Watson-Watt designed based on where the radio signal bounced back from. That meant it took lots of power. However, it worked, and a network of antennas were set up in time for the Battle of Britain. Their radar system, codenamed Chain Home could detect planes 100 miles away. That was plenty of time to scramble planes. The real difficulty was actually getting the information to the air fields to scramble the pilots quickly. That was eventually solved with a better communication system.

The Germans were aware of all the antenna, appearing along the British coast but decided it must be a communications system. Carrots also helped fool them! You may of heard that carrots help you see in the dark. That was just war-time propaganda invented to explain away the ability of the Brits to detect bombers so soon…a story was circulated that due to rationing Brits were eating lots of carrots so had incredible eye-sight as a result!

The Spitfires and their fighter pilots got all the glory and fame, but without radar they would not even have been off the ground before the bombers had dropped their payloads. Practical electronic engineering, Robert Watson-Watt and Arnold Wilkins were the real unsung heroes of the Battle of Britain.

– Paul Curzon, Queen Mary University of London

Postscript

In the 1950s Watson-Watt was caught speeding by a radar speed trap. He wrote a poem about it:

A Rough Justice

by Sir Robert Watson-Watt

Pity Sir Watson-Watt,
strange target of this radar plot

And thus, with others I can mention,
the victim of his own invention.

His magical all-seeing eye
enabled cloud-bound planes to fly

but now by some ironic twist
it spots the speeding motorist

and bites, no doubt with legal wit,
the hand that once created it.

…

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HMS Belfast: destroying the destroyer

by Paul Curzon, Queen Mary University of London

HMS Belfast

On the South Bank of the Thames in the centre of London lies the HMSBelfast. Now a museum ship, it once took part in one of the most significant sea battles of the Second World War. It fought the Scharnhorst in the last great sea battle based on the power of great guns. The Belfast needed more than just brilliant naval tactics to stand a chance. It needed help from computer science and electronic engineering too. In fact, without some brilliant computer science the battle would never have been fought in the first place. It came about because of the work of the code crackers at Bletchley Park.

Getting supplies across the Atlantic and then round to Russia was critical to both the British and Russian’s survival. By 1943 the threat of submarines had been countered. The battleship Tirpitz had also been disabled. However, the formidable battle cruiser Scharnhorst was left and it was the scourge of the Allied convoys. It sank 11 supply ships in one operation early in 1941. In another, it destroyed a weather station on Spitzbergen island that the Allies used to decide when convoys should set off.

By Christmas 1943 something had to be done about the Scharnhorst, but how to catch it, never mind stop it? A trap was needed. A pair of convoys going to and from Russia were a potential bait. The Nazis knew the target was there for the taking: the Scharnhorst was in a nearby port. Would they take that bait though, and how could the British battle ships be in the right place at the right time to not only stop it, but destroy it?

The Allies had an ace up their sleeve. Computer Science. By this point in the war a top secret team at Bletchley Park had worked out how to crack the Enigma encryption machine that was used to send coded messages by the German Navy. It was always easy to listen in to radio broadcasts, you just needed receivers in the right places, but if the messages were in code that didn’t help. You had to crack the day’s code to know what they were saying. Based on an improved approach, originally worked out by Polish mathematicians, the Brits could do it using special machines that were precursors to the first electronic computers. They intercepted messages that told them that Scharnhorst was preparing to leave. It was taking the bait.

The British had two groups of ships. The Belfast, the Norfolk and the Sheffield were coming from Russia protecting the returning convoy. The HMS Duke of York was tracking the new convoy heading to Russia. Both were keeping their distance so the convoys looked unprotected. They needed to know when and where the Scharnhorst would attack. Bletchley Park were listening in to everything though, and doing it so well they were reading the messages almost as soon as the Germans. At 2am on Boxing Day morning the Belfast got the message from Admiralty Head quarters that SCHARNHORST PROBABLY SAILED AT 1800 25 DECEMBER. A further radio signal from the Scharnhorst asking for a weather report allowed the spies to work out exactly where the ship was by picking up the signal from different listening stations and triangulating: drawing a line on a map from each station in the direction the radio signal came from. The point they meet is the ship’s location. This is an example of meta-data (information about a message rather than the message itself) giving vital information away. The spies had done their job. It was enough to tell Vice Admiral Burnett on the Belfast where the Scharnhorst was aiming to attack the convoys. They could lie in wait. At this point, electronic engineering mattered. The Belfast had better radar than the Scharnhorst. They detected its approach without the Scharnhorst having any idea they were there. The first the Captain of the Scharnhorst knew was when they were hit by shells from the Norfolk. The Belfast ended up out of position at the critical point though and couldn’t join in. The faster Scharnhorst turned tail and ran. The Brits had had their chance and blown it!

Burnett now needed luck and intuition. He guessed the Scharnhorst would try another attack on the convoy. They took up a new waiting position rather than actively trying to find the Scharnhorst as others wanted them to do. By midday the radar picked it up again. The trap was reset, though this time the initial surprise was lost. An all out battle began, with radar helping once again, this time as a way to aim shells even when the enemy wasn’t in sight. Having failed to reach the convoy undetected a second time the Scharnhorst retreated as the battle continued. What they didn’t know was that they were retreating deeper into the trap: heading directly towards the waiting Duke of York. The chasing Belfast stopped firing and dropped back, making the Scharnhorst crew think they were safe. In fact, they were still being followed and tracked by radar once more, though only by the Belfast as the other ships had actually been partially disabled. Had the Scharnhorst known, they could have just stopped and taken out the Belfast. After several hours of silent shadowing, the Belfast picked up the Duke of York on the radar, and were able to communicate with them. The Scharnhorst’s radar had been crippled in the battle and thought it was alone.

The Belfast fired shells that lit up the sky behind the Scharnhorst as seen from the Duke of York, then largely watched the battle. Luck was on their side: the Scharnhorst was crippled and then sunk by torpedoes. Over a thousand German sailors sadly died. The crew of the Belfast were well aware that it could just as easily have been them, sealed in to a giant metal coffin, as it sank, and so held a memorial for the dead Germans afterwards.

The Belfast didn’t fire the torpedoes that finally sank the Scharnhorst and was not the key player in the final battle. However, it was the one that was in the right place to save the convoy, thanks to the Enigma decrypts combined with the Vice Admiral’s intuition. It was also the one that pushed the Scharnhorst into the deadly trap, with its superior radar then giving it the advantage.

It is easy to under-estimate the importance of the Bletchley Park team to the war, but they repeatedly made the difference, as with the Scharnhorst, making Allied commanders look amazing. It is much easier to be amazing when you know everything the other side says! The Scharnhorst is just one example of how Computer Science and Electronic Engineering help win wars, and here, in the long run at least, save lives. Today having secure systems matters to everyone not just to those waging war. We rely on them for our bank system, our elections, as well as for our everyday privacy, whether from hacking newspapers or keeping our health records secret from ruthless companies wanting to exploit us. Cyber security matters.

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