Tuesday 10th March 11:13 am
Science of war 1: how to spot enemy guns using ancient geometry
Tuesday 3rd March 2015 1:20 pm
In the First World War, the most effective weapon system was artillery — the big guns. And, as a countermeasure, the most effective way to locate enemy artilleries so you could find then destroy it was sound ranging, which gave you the enemy’s guns’ exact location.
This technology was developed by a team led by 25-year-old Australian Nobel Prize winner and serving soldier William Lawrence Bragg, and his inspiration was that his bare bottom would get lifted off his toilet seat whenever a nearby artillery piece would fire even when he couldn’t hear the gun being fired.
The First World War, or The Great War, ran from mid-1914 to around late 1918, about four and a half years. Nine million military personnel and seven million civilians died in that bloody conflict. Furthermore over 22 million military were injured or seriously disabled.
The artillery was not particularly efficient. Over a 100 shells had to be fired to kill just one soldier. But it was terribly effective. Millions of dead people. Overall, during the course of World War 1 exploding shells and shrapnel fired by artillery killed more soldiers than any other weapon system.
At the beginning of The Great War neither side had effective methods that could pinpoint the location of enemy artillery. Sure they had flash spotters — brave men who would put themselves in locations where they could see the flash from the tip of the barrel as the big gun fired. Though, often the big guns were hidden out of sight.
Another method was to use the recently developed aircraft for spotting, but that didn’t work well in bad weather or at night. No, the solution lay in an ancient geometry technique called triangulation.
About 2500 years ago, the Greek mathematician and philosopher Thales was using the technique called ‘similar triangles’ to estimate the height of the pyramids of Egypt.
Around 250 AD, the Chinese scientist Pei Xui was using triangles to make accurate maps. Now the Romans didn’t ever seem to use triangulation, but around 1000 Arabian scholars were very familiar with triangulation to measure distances make maps and even measure the size of the Earth.
However, it took a few centuries for this Arabian mathematics to slowly percolate across to the West. So, in 1533, it was the cartographer Gemma Frisius who wrote about using triangulation to work out the exact locations of faraway places.
The principle is simple: suppose there is a mountain peak clearly visible in the distance directly in front of you. You accurately mark out a baseline, say two kilometres long. You walk to one end of your baseline and measure the angle to your mountain peak, you then walk to the other end of your baseline and measure a different angle to the mountain peak. Then, with these two angles and the baseline, use simple millennia-old geometry to give you the exact location of your mountain peak.
But then it gets messy on the battle field. The big problem is that you can’t reliably see where the enemy artillery is. However, you can almost always hear it.
Sound travels at around 300 metres in each second. You can easily pick up the sound with a microphone. However, because you usually can’t see the gun’s muzzle at the exact time it fired, you have no idea of the distance.
But there is a way around this.
Suppose you have lots of microphones located four kilometres back from the frontline and spread along the baseline, say nine kilometres long. The sound from the big artillery piece firing off would arrive at different microphones at different times. If you had enough microphones along a big enough baseline all you needed was some run-of-the-mill maths and you would know the exact location of the military regardless of the weather and the time of day.
That all sounds fine. But there was yet another fundamental problem. This problem was that often they couldn’t hear the enemy artillery firing off because of its location and the general din of war.
That problem was solved after the 25-year-old Australian Nobel Prize winner who was serving at the front got lifted off the toilet seat by the firing of the big guns just once too often. I’ll talk about that next time …
This blog first appeared on Dr Karl's Great Moments in Science
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