I think a crucial factor that is missing from your analysis is the difficulties for the attacker wanting to maneuver within the tunnel system.
In the Vietnam war and the ongoing Israel-Hamas war, the attacking forces appear to favor destroying the tunnels rather than exploiting them to maneuver. [1]
1. The layout of the tunnels is at least partially unknown to the attackers, which mitigates their ability to outflank the defenders. Yes, there may be paths that will allow the attacker to advance safely, but it may be difficult or impossible to reliably distinguish what this route is.
2. While maps of the tunnels could be produced through modern subsurface mapping, the defenders still must content with area denial devices (e.g. land mines, IEDs or booby traps). The confined nature of the tunnel system forces makes traps substantially more efficient.
3. The previous two considerations impose a substantial psychological burden on attacking advancing through the tunnels, even if they don’t encounter any resistance.
4. (Speculative)
Imagine a network so dense that in a typical 1km stretch of frontline, there are 100 separate tunnels passing beneath, such that you’d need at least 100 defensive chokepoints or else your line would have an exploitable hole.
The density and layout of the tunnels does not need to be constant throughout the network. The system of tunnels in regions the defender doesn’t expect to hold may have hundreds of entrances and intersections, being impossible for either side to defend effectively. But travel deeper into the defenders territory requires passing through only a limited number of well defended passageways. This favors the defenders using the peripheral, dense section of tunnel to employ hit-and-run tactics, rather than attempting to defend every passageways.
(My knowledge of subterranean warfare is based entirely on recreational reading.)
As a counterargument, the destruction of tunnels may be primarily due to the attacking force not intending on holding the territory permanently, and so there is little reason to preserve defensive structures.
Thanks! I don’t think the arguments you make undermine my core points. Point by point reply:
--Vietnam, Hamas, etc. have dense tunnel networks but not anywhere near dense enough. My theory predicts that there will be a phase shift at some point where it is easier to attack underground than aboveground. Clearly, it is not easier for Israel or the USA to attack underground than aboveground! And this is for several reasons, but one of them is that the networks aren’t dense enough—Hamas has many tunnels but there is still more attack surface on land than underground. --Yes, layout of tunnels is unknown to attackers. This is the thing I was referencing when I said you can’t scout from the air. --Again, with land mines and other such traps, as tunnel density increases eventually you will need more mines to defend underground than you would need to defend aboveground!!! At this point the phase shift occurs and attackers will prefer to attack underground, mines be damned—because the mines will actually be sparser / rarer underground! --Psychological burden is downstream of the already-discussed factors so if the above factors favor attacking underground, so will the psychological factors. --Yes, if the density of the network is not approximately constant, such that e.g. there is a ‘belt of low density’ around the city, then obviously that belt is a good place to set up defenses. This is fighting my hypothetical rather than disagreeing with it though; you are saying basically ‘yeah but what if it’s not dense in some places, then those places would be hard to attack.’ Yes. My point simply was that in place with sufficiently dense tunnel networks, underground attacks would be easier than overground attacks.
My reply definitely missed that you were talking about tunnel densities beyond what has been historically seen.
I’m inclined to agree with your argument that there is a phase shift, but it seems like it is less to do the fact that there are tunnels, and more to do with the geography becoming less tunnel-like and more open.
I have a couple thoughts on your model that aren’t direct refutations of anything you’ve said here:
I think the single term “density” is a too crude of a measure to get a good predictive model of how combat would play out. I’d expect there to be many parameters that describe a tunnel system and have a direct tactical impact. From your discussion of mines, I think “density” is referring to the number of edges in the network? I’d expect tunnel width, geometric layout etc would change how either side behaves.
I’m not sure about your background, but with zero hours of military combat under my belt, I doubt I can predict how modern subterranean combat plays out in tunnel systems with architectures that are beyond anything seen before in history.
I didn’t think through carefully what I mean by ‘density’ other than to say: I mean ‘# of chokepoints the defender needs to defend, in a typical stretch of frontline’ So, number of edges in the network (per sq km) sounds like a reasonable proxy for what I mean by density at least.
I also have zero hours of combat experience haha. I agree this is untested conjecture & that reality is likely to contain unexpected-by-me surprises that will make my toy model inaccurate or at least incomplete.
I think a crucial factor that is missing from your analysis is the difficulties for the attacker wanting to maneuver within the tunnel system.
In the Vietnam war and the ongoing Israel-Hamas war, the attacking forces appear to favor destroying the tunnels rather than exploiting them to maneuver. [1]
1. The layout of the tunnels is at least partially unknown to the attackers, which mitigates their ability to outflank the defenders. Yes, there may be paths that will allow the attacker to advance safely, but it may be difficult or impossible to reliably distinguish what this route is.
2. While maps of the tunnels could be produced through modern subsurface mapping, the defenders still must content with area denial devices (e.g. land mines, IEDs or booby traps). The confined nature of the tunnel system forces makes traps substantially more efficient.
3. The previous two considerations impose a substantial psychological burden on attacking advancing through the tunnels, even if they don’t encounter any resistance.
4. (Speculative)
The density and layout of the tunnels does not need to be constant throughout the network. The system of tunnels in regions the defender doesn’t expect to hold may have hundreds of entrances and intersections, being impossible for either side to defend effectively. But travel deeper into the defenders territory requires passing through only a limited number of well defended passageways. This favors the defenders using the peripheral, dense section of tunnel to employ hit-and-run tactics, rather than attempting to defend every passageways.
(My knowledge of subterranean warfare is based entirely on recreational reading.)
As a counterargument, the destruction of tunnels may be primarily due to the attacking force not intending on holding the territory permanently, and so there is little reason to preserve defensive structures.
Thanks! I don’t think the arguments you make undermine my core points. Point by point reply:
--Vietnam, Hamas, etc. have dense tunnel networks but not anywhere near dense enough. My theory predicts that there will be a phase shift at some point where it is easier to attack underground than aboveground. Clearly, it is not easier for Israel or the USA to attack underground than aboveground! And this is for several reasons, but one of them is that the networks aren’t dense enough—Hamas has many tunnels but there is still more attack surface on land than underground.
--Yes, layout of tunnels is unknown to attackers. This is the thing I was referencing when I said you can’t scout from the air.
--Again, with land mines and other such traps, as tunnel density increases eventually you will need more mines to defend underground than you would need to defend aboveground!!! At this point the phase shift occurs and attackers will prefer to attack underground, mines be damned—because the mines will actually be sparser / rarer underground!
--Psychological burden is downstream of the already-discussed factors so if the above factors favor attacking underground, so will the psychological factors.
--Yes, if the density of the network is not approximately constant, such that e.g. there is a ‘belt of low density’ around the city, then obviously that belt is a good place to set up defenses. This is fighting my hypothetical rather than disagreeing with it though; you are saying basically ‘yeah but what if it’s not dense in some places, then those places would be hard to attack.’ Yes. My point simply was that in place with sufficiently dense tunnel networks, underground attacks would be easier than overground attacks.
My reply definitely missed that you were talking about tunnel densities beyond what has been historically seen.
I’m inclined to agree with your argument that there is a phase shift, but it seems like it is less to do the fact that there are tunnels, and more to do with the geography becoming less tunnel-like and more open.
I have a couple thoughts on your model that aren’t direct refutations of anything you’ve said here:
I think the single term “density” is a too crude of a measure to get a good predictive model of how combat would play out. I’d expect there to be many parameters that describe a tunnel system and have a direct tactical impact. From your discussion of mines, I think “density” is referring to the number of edges in the network? I’d expect tunnel width, geometric layout etc would change how either side behaves.
I’m not sure about your background, but with zero hours of military combat under my belt, I doubt I can predict how modern subterranean combat plays out in tunnel systems with architectures that are beyond anything seen before in history.
OK, nice.
I didn’t think through carefully what I mean by ‘density’ other than to say: I mean ‘# of chokepoints the defender needs to defend, in a typical stretch of frontline’ So, number of edges in the network (per sq km) sounds like a reasonable proxy for what I mean by density at least.
I also have zero hours of combat experience haha. I agree this is untested conjecture & that reality is likely to contain unexpected-by-me surprises that will make my toy model inaccurate or at least incomplete.