It is widely believed that hostages in Gaza are being held by Hamas in a system of tunnels underneath the territory. This subterranean network is known to exist, but its size and interconnectedness remain unclear.
Drew Craig is a consultant geologist and a member of the International Working Group on subterranean warfare, based in England. He was on The Decibel to tell us what is known about the tunnels and how they’ve made the strategy of this war even more complicated.
This transcript has been edited and condensed for clarity and accuracy.
Menaka Raman-Wilms: So let’s talk about these tunnels. Hamas claims that this tunnel system stretches over 500 kilometres underground. The IDF – the Israel Defense Forces – they say the system is used to store weapons and includes military headquarters. But these tunnels do remain a bit of a mystery. So I guess, how do we know that they actually exist?
Drew Craig: They’re a mystery to the extent that we don’t really understand where they are. But Hamas themselves have been very open about bringing reporters down to these tunnel systems and effectively showing them around. A quick look on any one of these video platforms will show innumerable interviews and guided tours, showing a range of underground features. There are tunnels of – standard communication tunnels, we’d call it, to move from A to B. And then there are functional spaces that may have been for command and control or weapons engineering, or storage; they are also shown and are significant in size. So there’s a lot of information out there already to demonstrate the fact that these tunnels are there. What we just don’t understand is the true extent of how far they sit throughout the Gaza area, or indeed their orientation and sort of the overall scale and size of what the network looks like. What you may have is lots of smaller zones of networks, how interconnected those sort of little zones are, we don’t yet know.
Raman-Wilms: Let’s talk a little bit more about what we do know. Can you paint us a bit of a picture about what we have learned about these tunnels?
Craig: A lot of the footage you will commonly see will be a very narrow tunnel, about the width of a person, about the height of a person. Typically, with concrete panels along the sides, and an arched concrete cover over the ceiling. And these are concrete pre-forms that are effectively inserted into the tunnel once they’ve been dug. Now, these tunnels are actually constructed with relative ease, the underlying geology that [Hamas] has gone through is quite soft. It’s effectively marine sediments, sort of beach-like sediment. It’s poorly consolidated and by that, I mean you can dig and dig away quite easily. You don’t need to drill and blast, which is what you’d see in much harder rock. So, the tunnelling is relatively easy in that regard.
Raman-Wilms: How deep do these tunnels go?
Craig: You’re talking potentially, tens of metres [underground]. The geology will dictate that to some degree. The other factor that comes into play is the level of the water table. So the closer you are to the coast, or the closer you are to some of the water features, the drainage features that run through the terrain, the higher the water table will sit within the rocks. And what you don’t want to be doing is digging a tunnel then having it flood. But certainly the indications are that they’re, you know, tens of metres or getting down towards tens of metres deep, but some of the tunnels equally will be quite shallow. And we’ve seen tactical tunnels being used that have enabled troops to effectively pop up, to effect a quick attack of some sort and then to retreat back into the tunnel to get away. So let’s look at those as being tactical tunnels. And you compare those with the deeper communication tunnels that would interconnect to the mission spaces.
Raman-Wilms: What about the entrances to the tunnels? Do we know what they usually look like?
Craig: Wide and varied. So the tactical tunnels are potentially just an open hole, more in the rural areas, just covered over with scrub. But certainly there are indications that there are tunnel entrances that are within buildings. There was one video that came out about a week or so ago that showed an abandoned car in a car park. And the tunnel entrance actually came up inside the car. The concealment of these access points can be called a bit of an art form. But they are fixed points. So once they’re identified, they can then be closed off or exploited.
Raman-Wilms: What about things like communication power sources down there? What do we know about that?
Craig: Most of those tunnels will have power, or they will have communication cables running through them. If you’re underground and you’re in this confined space, you need to be turning the air over. So there will be some form of air conditioning involved as well. And so to that extent, [the tunnels] are relatively sophisticated, in that they have been fitted out with what we define as what’s called the umbilicals.
Raman-Wilms: So Hamas is thought to have begun digging these tunnels potentially in the mid-1990s. Maybe even before that – we don’t exactly know. But why were they built in the first place?
Craig: The original tunnels in Gaza, it goes back probably a couple of decades, if not longer. They were originally along the Egyptian border and they were predominantly for smuggling. And their scale and depth varied. And in some cases, you’re able to drive a car through a tunnel. Clearly, we’ve seen political changes in Gaza over the years as well. And now with Hamas, those tunnels are being dug exclusively for military means.
Raman-Wilms: I know that you’ve been in military tunnels before, not in Gaza but at the border between Lebanon and Israel. Can you tell us what that was like? What was it like being down there?
Craig: The one thing I was most struck about was the scale of what had been done. And I was there in December, 2019. Unlike in Gaza, you have hard-rock geology up in the north of Israel on the border of Lebanon – it’s dolomite and limestone. But the scale of some of those tunnels was rather incredible. There’s running water again, communication cables, telephones, power and the like, in order to build those tunnels in. So really quite dramatic, and impressive. It’s tight, it’s claustrophobic. I’ve been very lucky to visit a number of tunnels related to warfare around the world, ranging from the tunnels of Cu Chi in Vietnam, through to some of the tunnels within the Dolomites, which were used during World War I. And it’s incredibly claustrophobic, which I guess leads to the conclusion that underground warfare is not suited to everybody. It means both psychological conditioning and physical conditioning, plus the right equipment in order to be able to, you know, operate within that environment. The level of engineering was what I was particularly struck by.
Raman-Wilms: I guess I’m curious, because we’ve had major advances in technology. We can find things underwater, we can detect things in space. So why is it that tunnels, especially these ones under Gaza, why are they so hard for us to detect?
Craig: There’s lots of technology out there. I work in the mining sector. And we’ve got a myriad of systems that we can use from aircraft to satellites to systems that are on the ground. But sometimes you physically need to be above [the site], boots on the ground, in order to use a particular geophysics system. If you take that and put that into a military context, that requires securing a piece of ground and having the freedom of manoeuvre, to go about utilizing a piece of geophysical equipment in order to try and identify a target. But you don’t necessarily know what that means because we can’t quite X-ray down to the earth yet. That technology may be in our future but we don’t have it right now.
And then very much as we saw with the Israelis in 2018, on the Lebanese border, having identified targets through a variety of means, including traditional intelligence gathering as well, to then try and target those tunnels to intercept them. And what they did there was initially drill down to see whether they could intercept the tunnels, put CCTV cameras and other systems down there to then work out what was going on. In one case, the tunnels were destroyed through explosive means. The Israeli Defense Force gave a certain amount of verbal warning to what was going on through loudspeakers. They very overtly said, we’re going to blow this tunnel up and then they did so. And then the other means through which they denied access to the tunnels was pumping them full of concrete to block them. Anecdotally, if you go back, the Egyptians actually denied access through the tunnels between Egypt and Gaza a number of years ago by flooding them with sewage. But clearly, the presence or the potential presence of hostages is probably playing heavily on most people’s minds right now. And therefore, anything that’s being done is having to be thought through very, very carefully.
Raman-Wilms: I’m glad you brought up the hostages. Israel has stated, of course, that its goal is to destroy Hamas. And part of that mission has included targeting those tunnels. But we do believe that a lot of these hostages, if not all, are being held in these tunnels, right? Is it possible to destroy these tunnels without harming the hostages?
Craig: I used the term ‘denial’ earlier on. Most people, if you say I’m going to ‘deny’ that tunnel, will think are you going to fill it in or you’re going to destroy it through explosive means. And that might not necessarily be the case. You can deny at least partial use of a tunnel or the broader system, just by blocking off an entrance. And there’s been a bit in the media about the Israeli Defense Force using ‘sponge bombs’ – which effectively is a two part chemical that mixes and generates a foam that then hardens. So there are various other ways that you can deny access or deny utilization of a system without necessarily causing damage to the people who may be in that system.
Raman-Wilms: There is anticipation that fighting in this Israel-Hamas war will eventually go underground into these tunnels. What would it be like to fight down there?
Craig: Well, again, incredibly challenging. I think the approach so far from the IDF, appears to be ‘don’t engage in the tunnels.’ Hamas want to draw people in. And therefore, the IDF appears to be very reticent to do so. They’re leveraging drones via ground drones or aerial drones. They appear to be using military working dogs, using anything but putting a human being down into a tunnel. We’re seeing the tip of the iceberg in terms of what’s going on down there.
Raman-Wilms: With all this being said, will we ever actually have a full picture of these tunnels? Will we ever have the full extent of what’s down there?
Craig: No, I don’t think we will. But I think we will have a good idea of where those tunnels are. We have seen that there are hundreds of access points that are being identified [by the IDF]. So, I think we’ll get an idea of the distribution of the tunnels from those access points. As to what the web of tunnels potentially looks like? I don’t know. It very much depends on how much of the tunnels are actually destroyed. How much of that has been surveyed prior to destruction? And I guess that information will sit with the IDF and maybe we’ll learn in due course.