Before Radar: How The Hearing of "Aircraft Listeners" Saved Lives

SPEAKER_00 0:00 If you've ever been told you're a good listener, today you might be encouraged to become a therapist. But just a hundred years ago, being a good listener took a far more literal sense.

SPEAKER_01 0:10 Yeah, that's right. So instead, you could find yourself working for the military with enormous metal trumpets or domes strapped to your head. Yeah. It might look like some Kanye West-esque fashion statement, but this was deadly serious. Because before radar, this was genuinely somebody's job. Wearing some of the most bizarre looking headgear ever created, these so-called aircraft listeners would spend hours listening to the sky, trying to detect the faint sound of an enemy bomber before anyone could see it.

SPEAKER_00 1:01 What they were doing was incredibly important. So some had four enormous horns, others looked like giant metal ears, and Britain even built enormous concrete structures along the coast designed to listen across the English Channel. And this was because, you know, somewhere in the darkness, enemy bombers might be approaching, and they had to hear them before they arrived.

SPEAKER_01 1:26 So, did these ridiculous-looking machines actually work? And how did people whose job was simply to listen become a vital part of the country's air defences? Only to then find themselves virtually obsolete almost overnight. This is what we did before.

SPEAKER_00 1:47 I'm Matt. And I'm Ollie, and today we're exploring what it was actually like to be an aircraft listener, the bizarre equipment they used, the conditions they worked in, and how one new invention made an apparently vital job disappear almost as quickly as it started.

SPEAKER_01 2:06 So to understand why anyone thought giant ears were a good idea, we need to go back to the first world war because aircraft had suddenly created a completely new military problem. For basically all of human history, if if an enemy wanted to attack your city, they generally had to approach you on the ground or by sea, which gave you at least some chance of seeing them coming.

SPEAKER_00 2:31 Yeah, but by the time the war arrives, you've got aircraft which can fly over at at high speed, right?

SPEAKER_01 2:38 Yeah, exactly. And in in the First World War, aircraft weren't initially the terrifying bombers we'd later associate with the Second World War, and beyond that, they were mainly used for reconnaissance.

SPEAKER_00 2:50 And Britain soon found itself facing attacks from German airships, later bombers. And the the problem was this was well, this was a brand new problem to have. Airplanes in warfare were a new concept, and there was no radar as we have it today to detect them.

SPEAKER_01 3:06 Yeah, the concept of radar didn't exist. So if an enemy aircraft approached at night or through cloud, you couldn't necessarily see it, but you could hear it. Aircraft engines at the time were incredibly loud. So in a world without radar or other advanced technologies to detect them, the initial solution was basically let's get people to listen out for them. Yeah, so the initial technology was basically just people's ears. Yeah, pretty much, yeah. Observers would listen for aircraft and try to work out where the sound was coming from.

SPEAKER_00 3:43 But that's quite a challenge. I'm trying to imagine myself doing that. So sometimes I can hear that there's a plane overhead, right? Like during the red arrows displays or something, or even you know, in in the vast distance, if you're on a in a quiet field or something. But I don't think I can use my ears to accurately know where the aircraft is coming from, like what direction it's going. I know it's near, probably if I can hear it, but I would have to scan the sky visually to actually pinpoint where it's coming from, especially if it's already flown by and I'm hearing it because of the delay of the speed of sound. So there's a lot of problems there.

SPEAKER_01 4:21 Yeah, exactly. That those are problems, especially as well if you can't then see it because it's out of your visual line of sight. Your brain is actually pretty good at locating sounds because you have two ears, or most of us do. Generally, if a sound comes from your left, it reaches your left ear slightly before your right, so your brain can estimate from the tiny differences in timing and volume that it probably came from that direction. So conceptually it can work well, but engineers thought they could do better than biology. By making massive ears. Yeah, obviously.

SPEAKER_00 4:58 Yeah, and that's where things start to look quite ridiculous. Um, so during the First World War, several countries began experimenting with acoustic locators, and these came in all sorts of shapes. But one of the most recognizable British designs had enormous horns mounted on a rotating frame. So you can kind of imagine four gramophone horns, except each one is roughly the size of a human being, and there's a soldier sitting underneath them with tubes running from the horns into his ears.

SPEAKER_01 5:32 So the the aircraft listeners' job was literally just to move the horns around and listen out. And if they heard something, they would slowly rotate like the entire machine, and as the aircraft sound became louder or quieter in each ear, they could adjust them, the horns, until the sound seemed kind of balanced to them.

SPEAKER_00 5:55 But but it wasn't always enough just to have one person on these uh systems, right? There on some of the four-horn systems, you had multiple people operating them.

SPEAKER_01 6:05 Yes. Um, sometimes the configuration and each country, and also over time, this was different. Each country had their own uh way of doing things, but there was a means where two people would use two horns each.

SPEAKER_00 6:21 So one listener was effectively responsible for left and right, and then the other one was responsible for up and down, so they could sort of share the cognitive load, I guess.

SPEAKER_01 6:30 Yeah, yeah, exactly. Um two human beings were basically acting as part of one giant mechanical ear.

SPEAKER_00 6:38 I wonder how mu how quickly this all had to happen. Um, the moving the giant dishes and uh communicating to each other, whether it's up, whether it's down, whether it's left, whether it's right. Because, you know, you can imagine if it takes too long, the plane's sort of gone and your opportunities disappeared.

SPEAKER_01 6:54 Yeah, yeah. And um we'll get into it a bit later, maybe, but there's you you did have to factor in that time, of course, because um when you're trying to pinpoint where something that's moving is, especially when you have to factor in the speed of sound, you also have to factor in the time it takes for the crew to do their job and to relay that information and everything else. So it actually gets pretty complicated. Because yes, once they have done this, they then have to pass that information to searchlight crews or anti-aircraft batteries, and then you're just more prepared than just relying on your mushy human ears. Yeah, uh although presumably you needed like pretty good hearing to do this job. Yeah, you you'd think so. I think I'd struggle with this one after going to a few too many gigs. Um but but but interestingly, being a good military listener wasn't actually just about having really good sensitive ears, it was also a skill that they trained. During the First World War, specialist military listeners, sometimes described as military auditors, were actually trained to identify the direction and position of sounds. They didn't just turn up to an interview and say, My wife says I'm a good listener, and get the job based on their natural skill alone.

SPEAKER_00 8:19 Yeah, I wonder how many people's wives would have said um they were good listeners anyway. Yeah, that's true. And the more you think about it, it sounds deceptively easy, or maybe even boring, but imagine what you're actually trying to do. You're sitting outside, probably at night, you've got wind vehicles, if there's an active war going on, you might have artillery, the sound of explosions, gunfire, people shouting, you know, loads of noise. There could be multiple aircraft. And somewhere amongst all of that, you need to identify the low drone of one particular aircraft, then work out exactly where it's coming from.

SPEAKER_01 8:57 Yeah, and while that aircraft is moving, not to mention remaining focused during the inevitable hours of not much happening. I think it would be incredibly difficult, to be honest. And sound doesn't arrive instantly, particularly notable when you're listening at longer distances like they were. And that's one of the biggest problems that these systems faced.

SPEAKER_00 9:20 And I wonder if they got so sophisticated at this that they could detect the actual exact aircraft that was flying through the sky. Because as an audio editor, uh, I can just look at a waveform and I can uh see an um without listening to the um. And you know, once you've developed and refined a skill, you start to be able to pick up things the ordinary person wouldn't. And I imagine for for them they could determine whether it was a certain type of aircraft.

SPEAKER_01 9:45 Yeah, I I think so. I mean, I this is a bizarre kind of comparison, but I'm I'm quite a fan of Formula One, and I've seen um I've seen a few things where they've shown drivers, like they just play an engine from an era of F1, and it and the driver goes, Oh yeah, that's a Ferrari V10. Like that's amazing. But it's a Ferrari V10. So I suspect if your job is to listen for aircraft, you're like, Oh yeah, that's one of those German biplanes, or you know, so yeah, I imagine so. I'm I'm not sure there must be research on this, or there must be some some further information on that one, but I imagine so.

SPEAKER_00 10:28 But back to your point, Matt, about the speed of sound and the fact that you know often it's delayed, of course. Yes. Um so how did they get around this?

SPEAKER_01 10:38 So sound travels at roughly 340 meters per second, but light travels about 300,000 kilometers per second. So the 340 meters per second for sound sounds fast until you're trying to shoot down an aircraft. And this problem gets bigger the further away the the aircraft is. So imagine it's 3.4 kilometers away. That means that the sound that you hear is 10 seconds old. So it could have moved quite a lot. By the end of World War I, some of these planes could travel up to 240 kilometers an hour, so it could have moved over half a kilometre in that time. You know, the further away it it is, the more it would have moved. And to your point before, about then you have to factor in the time it takes for the operators to say it's over there and everything, the aircraft has probably already moved quite quite significantly in some cases.

SPEAKER_00 11:34 Yeah, so they eventually applied something called sound lag corrections, which could sort of um you know make accountances for the fact that this lag existed. And they got really clever with this. So, according to the Wallsdorp Museum, there were some mechanical systems for predicting where the aircraft actually was, and they would need multiple operators for this. So, one to listen, one to plot a likely flight path, and then use tables to determine where it is based on the aircraft's estimated speed, altitude, and even the time to process the observations, the time it took for them to process it all. So, you know, you could say you heard the aircraft there, so it's probably here right now.

SPEAKER_01 12:16 So on the surface, it sounds in some ways like it could have been a fairly safe or easy job compared to some military jobs. But there's another fairly obvious problem with being an aircraft listener. If you're close enough to detect enemy bombers in a place that matters to detect them, you may be somewhere the enemy wants to bomb.

SPEAKER_00 12:39 Yeah, because here we're we've just discussed proximity does matter. And these weren't people listening from a safe control room hundreds of miles away. Acoustic locators formed part of air defense systems. So their job was to provide warning or help searchlights and anti-aircraft crews find enemy aircraft, which meant doing your job during air attacks and often in the darkness as well. Yeah, not to mention there was also another danger, your hearing. Yeah, that's right. And military researchers, uh, historians, theorists of sound like Gasha Uzunyan recognized that intense noise could cause listener fatigue and hearing damage. And that's slightly unfortunate when your entire military usefulness depends on your ears. And there are accounts from the first world war of soldiers suffering sudden deafness during battle, and even gunners whose ears bled from the noise.

SPEAKER_01 13:35 Which must have made the job of listening for a quiet noise in the distance pretty difficult. But like many innovations, it did keep developing, not just in terms of the complex calculations that they were able to do to determine location. Engineers went bigger, much bigger. Because they thought if a horn could collect sound, why not build something enormous to collect even more? And this led to one of the strangest pieces of Britain's early warning system, the sound mirror. It kind of sounds like something from sci-fi. Yeah, and it looks like it as well. Along parts of the British coast, I wasn't aware of this actually. There are these enormous curved concrete structures, and some of them look like giant satellite dishes or you know, big curved walls, but their purpose was the same. It was to capture the distant sound of approaching aircraft and to focus that onto like a microphone or a listening device positioned in front of it. So it was essentially a gigantic concrete ear. So how big are we talking with this giant concrete ear? Well, some of these uh sound mirrors were around 20 to 30 feet across. And in Kent, they eventually built an enormous curved concrete wall that was around 200 feet long. The idea was that the aircraft approaching Britain from continental Europe could potentially be heard before they reached the coast.

SPEAKER_00 15:08 Yeah, and you can imagine that those extra minutes of warning were incredibly valuable because every minute meant more time to prepare anti-aircraft defences. But the obvious question, I think, is did any of this actually work? The answer is yes.

SPEAKER_01 15:22 Well, sort of. Ear trumpets as hearing aids, they they weren't a new concept. I think they were around even from the 17th century or something.

SPEAKER_00 15:32 And as we mentioned, this was happening all around the world, so you know, it they must have worked. There's actually a famous photograph from the 1930s showing Japanese soldiers operating enormous acoustic locators with huge curved horns, and these were nicknamed sometimes uh war tubers. But clearly, we don't have people sitting around airports with enormous trumpets on their ears anymore. So what happened?

SPEAKER_01 15:57 Well, the obvious answer is that radar made them redundant. But the the reason for this really is that, well, aircraft got better and acoustic detection just couldn't keep up.

SPEAKER_00 16:10 Yeah, because during the first world war, aircraft were relatively slow, but through the 1920s and the 30s, they became dramatically faster and they could fly higher. So it was a real problem at that point to start listening out for them.

SPEAKER_01 16:23 Yeah, yeah. As as aircraft got faster and higher, it made it harder for people, and of course, the limitations of the speed of sound to keep up with it. It's it was just as simple as that.

SPEAKER_00 16:36 Yeah, so what air defence really needed was something that could detect aircraft much further away and a lot faster without relying on someone having extremely good ears. So the answer to that, of course, was radar. Exactly. Um, during the 1930s, Britain began rapidly developing radar. So instead of waiting for sound produced by an aircraft to reach you, radar transmitted radio waves, and those waves travel outward, reflecting from objects like aircraft and then returning to a receiver.

SPEAKER_01 17:07 Yeah, and since radio waves travel at roughly the speed of light, suddenly you could detect aircraft at far greater distances and far greater accuracy than relying on the speed of sound. Yeah, which sadly makes giant ears kind of redundant. Yeah, and very quickly too, Britain constructed the chain home radar network along its coast before the second world war.

SPEAKER_00 17:33 Although sound locators didn't disappear instantly, so some continued to be used alongside searchlights and anti-aircraft units, including during the Second World War, because they could still provide an initial bearing for searchlights. But technologically, their time was up.

SPEAKER_01 17:51 Yeah, so in the space of only a few decades, aircraft listening went from cutting-edge super important military technology to basically obsolete.

SPEAKER_00 18:03 Yeah, and that's what makes it such an interesting job because there was a period of time where they dedicated a lot of time, effort, money training their ears, learning to distinguish aircraft sounds, and then suddenly it was gone. They even took lifelong hearing damage potentially as a cost for this great service. And I don't know, it has some bearing on the modern age, in my opinion. You know, as we see various jobs fall by the wayside, uh, thanks to advances in technology and artificial intelligence, all these things that people have trained their whole lives to do suddenly become obsolete. And it's very much the same for the aircraft listener. And in some ways, I imagine for them it would have been quite devastating at radar coming in and this job that they had done all their life suddenly wasn't needed anymore. Yeah, definitely.

SPEAKER_01 18:49 I think it's the it's the same thing uh for anyone, right? Like people will have dedicated their lives and trained, you know, they know that this is their career, and almost overnight, something better and inhuman really has replaced them. So it must have been pretty brutal for them. Well, thank you so much for listening. This is what we did before. I'm Ollie. And I'm Matt. If you enjoyed this journey into one of history's strangest forgotten jobs, please let us know in the comments and please do like and subscribe, it really helps us out.