Tag: World War II

Sea sounds sink ships

A shoal of silvery blue fish densely packed and swimming together
Shoal of fish in the Galapagos image by Christopher Chilton from Pixabay

You might think that under the sea things are nice and quiet, but something fishy is going on down there. Our oceans are filled with natural noise. This is called ambient noise and comes from lots of different sources: from the sound of winds blowing waves on the surface, rain, distant ships and even underwater volcanoes. For undersea marine life that relies on sonar or other acoustic ways to communicate and navigate all the extra ocean noise pollution that human activities, such as undersea mining and powerful ships sonars, have caused, is an increasing problem. But it’s not only the marine life that is affected by the levels of sea sounds, submarines also need to know something about all that ambient noise.

In the early 1900s the aptly named ‘Submarine signal company’ made their living by installing undersea bells near lighthouses. The sound of these bells were a warning to mariners about the impending navigation hazards: an auditory version of the lighthouse light.

The Second World War led to scientists taking undersea ambient noise more seriously as they developed deadly acoustic mines. These are explosive mines triggered by the sound of a passing ship. To make the acoustic trigger work reliably the scientists needed to measure ambient sound, or the mines would explode while simply floating in the water. Measurements of sound frequencies were taken in harbours and coastal waters, and from these a mathematical formula was computed that gave them the ‘Knudsen curves’. Named after the scientist who led the research these curves showed how undersea sound frequencies varies with surface wind speed and wave height. They allowed the acoustic triggers to be set to make the mines most effective.

– Peter McOwan, Queen Mary University of London

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Navajo Code Talkers

Three Navajo Code talkers in WWII
Navajo Code Talkers, Image from National Archives at College Park, Public domain, via Wikimedia Commons

Bletchley Park, the British code cracking centre helped win World War II, but it is not just breaking codes and ciphers that wins wars, creating unbreakable ones to keep your own secrets safe matters too. Bletchley Park wasn’t the first or only time a secret cryptography team helped win battles or even wars. In World War I secret messages had been successfully sent using Choctaw, the language of a tribe of Native Americans, including to help organise a surprise attack. It worked with their messages left un-cracked. This led to an even more successful code-creating team in World War II based on Navajo. The Navajo “Code Talkers” as they were called, could encode, transmit and decode messages in minutes when it would take hours using conventional codes and ciphers.

In World War II, the US forces used a range of Native American languages to communicate, but a code based on a native Indian language, Navajo, was especially successful. The use of a Navajo-based code was the idea of Philip Johnston after the attack on Pearl Harbour. His parents were missionaries so he had grown up on a Navajo reservation, speaking the language fluently despite how difficult it was. Aged only 9, he acted as an interpreter for a group who went to Washington to try to improve Indian rights.

He suggested using Navajo as a secret language and enlisted in the marines to help bring the idea to fruition. He thought it would work as a secret code because there was no written version of Navajo. It was a purely a spoken language. That meant he was one of very few people who were not Navajo who could speak it. It was also a complex language unlike any other language. The US marines agreed to trial the idea. 

To prove it would work, Johnston had Navajo transmit messages in the way they would need to on the battlefield. They could do it close to 100 times faster than it would take using standard cipher machines. That clinched it. 

Many Navajo had enlisted after Pearl Harbour and a platoon soley of Navajo were recruited to the project, including a 15 year old, William Dean Yazzie. However, they didn’t just speak in Navajo to transmit messages. The original 29 Navajo recruited worked out the details of the code they would use. Once deployed to the Pacific a group of them also met to further improve the code. None of it was written down apart from in training manuals that did not leave the training site, so there was no chance the code book could be captured in battle. All those involved memorised it and practiced sending messages quickly and accurately. Messages were also always spoken, eg over radio and never written down, making it harder for the code to be cracked based on analysing intercepted messages.

Commonly needed words, like ‘difficult’ or ‘final’ had direct Navajo code words (NA-NE-KLAH and TAH-AH-KWO-DIH). However for critical words (countries, kinds of planes, kinds of ships, etc) they first swapped English words for other English words using one code. They then translated those words into Navajo. That meant even a Navajo speaker outside their trained group wouldn’t immediately understand a message. The code, for example, used birds names in place of kinds of planes. So the English code word for a bomber plane was Buzzard. But then the Navajo for Buzzard was actually used: (JAY-SHO). 

Another part of the code was to use Navajo words for letters of the alphabet, so A is for ant translated to WOL-LA-CHE in Navajo. However, to make this more secure two other words stood for A too (apple: BE-LA-SANA and axe: TSE-NILL). Each letter had three alternatives like this and any of the three could be used.

Finally the way that it was used meant a message would always just be a series of unconnected words making no sense even to a Navajo speaker.

The code talkers played a key part in many battles including the iconic battle of Iwo Jima, capturing the heavily defended Japanese controlled island of that name. The US Major responsible for communications said of the battle, “Were it not for the Navajos, the Marines would never have taken Iwo Jima.”

Not only did it make communications much faster than they would have been, unlike other US codes and ciphers, the code talker’s code was never cracked … all thanks to the Navajo team who devised it.

– Paul Curzon, Queen Mary University of London

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Front cover of CS4FN issue 29 - Diversity in Computing

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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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