“Mr. President, we cannot allow a mineshaft gap!” exclaimed General “Buck” Turgidson, in the 1964 film “Dr. Strangelove”. 

The public was not prepared. The casual observer of news videos showing relentless Israeli bombing in Gaza can readily wonder if it is disproportionate to the military goals.  Tens of thousands of civilians killed because of a bunch of tunnels?  There was little attention focused on the Hamas threat, especially the tunnel threat in the period before Hamas attacked.  In contrast, Prime Minister Netanyahu has spun up the world about the Iran nuclear threat and the potential necessity for Israel to conduct a massive air attack against Iran’s underground nuclear facilities.  But the threat of Hamas and especially its tunnels was not highlighted.  If you asked students of the Middle East last year to list the major military threats to Israel—few if any would have noted tunnels.

Yet, Hamas constructed a huge maze of tunnels throughout the Gaza Strip.  How or why did this happen without drawing broad attention?  Tunnels have been an implement of warfare forever.  They were built offensively to attack castles in the Middle Ages. Defensively they have been used to conceal personnel or weapons, and to transport material clandestinely. East Berliners escaped to the West by tunnelling under the Berlin Wall.  American forces were vexed by tunnels employed by the Viet Cong. And in the Middle East there is recent experience of tunnel warfare in Syria where Al Nusra used them in urban areas.  ISIS used them in the battle for Mosul. 

In military and security studies, there is little focus on Tunnel Warfare, or “Subterranean operations”.  I include myself in overlooking their import—and I spent substantial effort investigating underground facilities in Iraq as potential concealment locations for WMD while directing the Iraq Survey Group in 2004.  The US national security establishment hasn’t focused on a subterranean mission.  Maybe we needed a General Buck Turgidson to draw attention a Tunnel capability gap. 

Proportionality.  The fact that Hamas initiated this war is readily understood.  What’s harder to grasp is why the underground network is so important and requires continuous bombing for months to destroy?  Even more critical is the magnitude of destruction to civilian surface inhabitants to get at the subterranean enemy.  Endless videos of the horrors endured by surface civilians combined with no publicly understandable image of the underground threat leaves Israel struggling to justify their military response.   The vague objective of “destroying Hamas” is not compelling when there are vivid videos of above ground despair and little to no imagery of the subterranean threat.

The rationales do not resonate with average audiences.  Older Americans will recall the hollow rationale during the Tet Offensive during the Vietnam war, “We had to destroy the village in order to save it.”   Huh?

Again, the public was not prepared in advance for the magnitude of the war that surprised Israel and the world on October 7, 2023.  This is one key consequence of the policy and intelligence failures prior to October 7.

Simple questions present themselves.  How can you dig 500 km of tunnels without anyone knowing?   Where did they put all the dirt?  Nothing showed up in overhead imagery?  Hundreds of workers were involved in digging, pouring concrete, running conduits, air ventilation systems, creating entrance and egress points. Israel must have received reports on such activity. And, if they did know, didn’t they appreciate the threat?   

Few have focused on subterranean warfare in the United States, but in Gaza, it’s on a par with other established military domains: Air, Land, Sea, Cyber, and Space.  Didn’t Israel?

Well, they must have “turned a blind eye” to it as the saying goes because there was a dress rehearsal of this attack in July-August 2014.  Americans who do not follow the middle east closely would probably not recall this prior Hamas-Israel conflict—especially since it occurred in the middle of the horrific ISIS war which dominated headlines.

The Dress Rehearsal.  In July 2014, Hamas used tunnels from Gaza to attack Israel. In many ways, this was a test run of the techniques witnessed in the current conflict.  Hamas virtually repeated all the same tactics on October 7, but amped up the scale and the horror.  Israel’s limited objective in the 2014 conflict was to destroy the tunnels that crossed the Israeli border.  Maybe world attention was focused on the ISIS war in Syrian and Iraq, but the 2014 Israel-Hamas conflict should not have been taken lightly. 

There is a fascinating analysis of Hamas’ 2014 tunnel networks detailed by Dr. Eado Hecht (an Israeli defense analyst specializing in military theory and military history) in a 45-page report he presented to the UN Commission of Inquiry on the 2014 Gaza Conflict titled, “The Tunnels in Gaza” in February 2015 (https://www.mideastdig.com/wp-content/uploads/2017/01/testimony.pdf).

Dr. Hecht identified all the military challenges presented by Hamas’s tunnel network.  He even described many of the locations and their collocations with civilian infrastructure (including under the Shiva Hospital).  Nothing that happened on October 7, 2023 would have surprised anyone who read Dr. Hecht’s report.  For example, he said the following concerning the Hamas actions in 2014:

“In May 2014 the Israel Security Agency published an alert that the Hamas was preparing to conduct a massive terrorist attack probably sometime in the summer or autumn of 2014. Hamas fighters captured and interrogated during the Israeli ground forces operation in Gaza in late July – early August 2014 revealed that the final plan was to simultaneously attack a number of Israeli villages, each one with 10 to 15 terrorists. Had this plan been successfully realized it would have resulted in hundreds of Israel civilian casualties.” 

Dr. Hecht was correct. 

(Note: At end of this piece I have copied some segments of the Hecht report that illuminate the tunnel dangers and challenges.  It’s sadly fascinating reading.) 

Maybe it’s just too hard. Israel also had experience with tunnel threats in the 2006 war with Hezbollah.  If anyone has expertise in the offensive threat of tunnels, it’s Israel.  And yet, it seems to have eluded sufficient attention.  There is not a great body of doctrine or academic literature on subterranean warfare—even in Israel.  There are no large organizations or procurement programs in the (US) military for the conduct of offensive or defensive subterranean warfare.  It has been viewed as an adjunct to other combat missions, not a unique specialty. Partly, I suspect, this is because it is very difficult.  

Israel knew about the existence of tunnels but did not, or could not, develop good technological or doctrinal methods for operating in a battlefield prepared by Hamas years in advance.  Hamas was probably as savvy at subterranean operations as anyone.  They doubled down after their 2014 war.  Israel has been addressing tunnels as a security issue in various components, e.g. border security, smuggling, weapons caching, command and control functions, etc. 

However, in the current conflict is the battle is being taken to Hamas inside Gaza, not responding to border transgressions.  It does not appear, to an outsider, that Israel had a strategy or technical capacity to operate in a battlefield prepared by the enemy in advance for subterranean operations.  What else can explain the lack of any better concept for conducting subterranean warfare in an urban environment than brute force bombing of the tunnels and any co-located civilian structures?  Moreover, that bombing seems to reveal very little detailed knowledge of underground facilities. Precision guided munitions can reduce collateral damage only if you have precision knowledge of target location.  Clearly, the IDF does not.

Some belated attention, has been drawn to subterranean warfare in light of October 7.

USA Today ran a very good summary of the Israeli Tunnel problem on 30 October 2023 by Rick Jervis—early in the massive Israeli bombing campaign (https://www.usatoday.com/story/news/investigations/2023/10/30/hamas-tunnels-israel-ground-invasion/71373315007/).  He quoted American military officers who had been aware of tunnels as a military problem and the paucity of good solutions.

There are at least three prescient academic articles foreshadowing the military challenges of operating in and holding territory in a conflict on ground prepared by an enemy expert in tunnel warfare.  

IDF Colonel (Res.) Ati Shelah published an article dated 15 July 2014 titled “Maneuvering in the Underground”, in “Israel Defense”.  (https://www.israeldefense.co.il/content/תמרון-בתת-הקרקע) This later is in Hebrew but a google translation yields a pretty comprehensible English translation.

Raphael Marcus of the Insurgency Research Group, Department of War Studies, King’s College London, UK authored a piece dated 12 April 2017 (after the 2014 conflict) titled, “Learning ‘Under Fire’: Israel’s improvised military adaptation to Hamas tunnel warfare”. (https://www.tandfonline.com/doi/full/10.1080/01402390.2017.1307744?src=recsys)

Daphne Richemond-Barak and Stefan Voiculescu-Holvad published, “The Rise of Tunnel Warfare as a Tactical, Operational, and Strategic Issue”, in Studies in Conflict and Terrorism published 23 August 2023. (https://www.tandfonline.com/doi/full/10.1080/1057610X.2023.2244191)

But is the action proportionate?

Part of the crisis facing the US from the Israeli war with Hamas comes from the apparent disproportionate military collateral civilian casualties.  On the surface, the costly damage is apparent and broadcast real-time around the world.  Below the surface, the importance of the target is obscure, indeed, invisible to global audiences.   On the surface there are thousands of horror stories endured by civilians born in the wrong place.  In contrast to the broadly socialized Iran nuclear threat, the Hamas tunnel threat is not obvious.  The argument about denying a sanctuary to an enemy dedicated to your destruction was not made in advance.  

Syrian tactics.  Syrian confronted the problem of urban enemy tunnels with chlorine gas.  International condemnation of this was swift.  It was, of course, a blatant violation of the Chemical Weapons Convention.  Yet, in a very perverse way, chlorine—which is heavier than air and sinks–or noxious gases could be used to flush enemy out of urban tunnels with much less collateral damage. I am in no way advocating this.  But, perhaps Hamas considered this as one of their reasons for taking hostages.  One wonders if Israel ever considered this as a way of reducing civilian casualties.  

Subterranean conflict is a massive challenge.  To understand and judge the proportionality of Israel’s campaign in Gaza it’s important to have some knowledge of this subject. Just watching television videos is insufficient.  The above (and below) is intended to offer an introduction. There may be no good answers.

Note:  I have copied below some selected excerpts from the 2015 Eado Hecht Report(https://www.mideastdig.com/wp-content/uploads/2017/01/testimony.pdf). They provide some details on the IDF challenges in conflict involving subterranean structures from eight years ago.

“33. The typical cross-border tunnel was dug at a depth of 15 to 25 meters underground. It was approximately 1.5 meters wide and nearly 2 meters high – a few were wider to enable moving heavier equipment through them (as noted above, in one tunnel the Israeli forces found motor-cycles the Hamas intended to use on exiting the tunnel inside Israel). The sides and roof were lined with concrete. It had electricity for lighting and other uses and telephone wires. In some there were rooms for storing equipment or allowing personnel to stay under ground for extended periods. Some tunnels had more than one branch. In addition to the entrance (usually approximately a meter or slightly more across) there were ventilation shafts dug every few hundred meters.” 

“Detecting the tunnels is a very very difficult task. 

36. To date there is no trustworthy detection technology for tunnels of this size at this depth. All attempts to use radars etc. have proven insufficiently reliable or total failures. The only partially reliable technology that does exist is the use of sensitive microphones inserted into the ground to listen for sounds of digging. However, to hear the digging the microphones have to be fairly close to the location of the tunnel so you have to know in advance where to put them and this requires other sources of intelligence. Also, the sound of digging can be muffled by working slowly with specifically designed manual tools and other sounds in the vicinity can interfere too. Furthermore, once the tunnel is complete the microphones have nothing to hear. 

37. Given the lack of technology the only way of detecting the tunnels is to acquire intelligence from other sources – either listening in to Hamas communications in case they talk about the locations; or stealing documents on the plans of the tunnels from Hamas headquarters; or infiltrating a spy into the digging operations. Hamas is fully aware of these intelligence capabilities and took especial care to maintain the secrecy of the tunnel projects. For example: discussions on the project were not allowed on telephone communications, the diggers were taken to the sites in completely closed vehicles so they could not see where they were and kept underground for a few days at a stretch, building materials taken to the sites and earth removed from the sites were camouflaged, the entrances were all inside buildings and ventilation shafts were camouflaged, etc.” 

“Tunnels inside Gaza

43. The tunnels dug inside Gaza are the most varied in use (and therefore also in location, shape and style of building). The different uses are: 

1. Underground mortar and rocket-launcher positions. 
2. Command centers 
3. Safe-havens for Hamas forces to avoid Israeli fire and to rest. 
4. Hidden fighting positions from which small-arms fire can be directed onto Israeli troops in their vicinity. 
5. Storage tunnels for weapons and equipment. 
6. Tactical maneuver tunnels for moving troops or equipment between different locations inside Gaza while hidden from Israeli observation. 
7. The last type of tunnels is useful also to conduct surprise attacks on Israeli troops from unexpected directions and especially to attempt to kidnap Israeli soldiers.”

“44. There is absolutely no information available from which one can deduce how many tunnels all together there are in Gaza – but there were at least several hundred such tunnels of all the above categories and probably more than a thousand – most of them belonging to the last three categories!Of the approximately 5,000 targets attacked by the Israeli air force, approximately 200 were reported to be storage tunnels. Again it must be reiterated – most of Hamas’ combat power is located above ground, hidden in buildings in residential areas, often in multi-storey apartment buildings in which a few apartments, scattered randomly on all floors, are set aside for Hamas use (command posts, weapons stores, etc.)” 

46. The locations of the tunnels in general and of the entrance and exit points of tunnels in particular, of the non-cross-border tunnels inside Gaza are much more varied than those of the cross-border tunnels: 

1. Some are located underneath open fields with the entrances and exits camouflaged under huts supposedly built by farmers for resting or storing their tools. 
2. Others are located underneath the residential areas. Most of the entrances and exits are from the ground floors or basements of residential homes or of public buildings – including Mosques (for example the above-mentioned Khuza’a Mosque), hospitals (The chief headquarters of the Hamas is believed to be under the Al-Shifa hospital^[1]), medical clinics, schools and other public service buildings. Some entrances, exits and ventilation holes are located outside buildings and camouflaged to appear to be ‘innocent’ civilian locations, covered by vegetation etc. or even disguised to resemble merey pot- holes in the street. 

47. It should be noted that many tunnels had multiple entrances so that even if the Israelis found and destroyed one entrance the Hamas could often still use that tunnel or even redig the destroyed entrance. 

48. Here too it should be noted that most of the entrances were surrounded by explosive devices – some to be triggered by booby-traps and some to be triggered by Hamas observers watching from adjacent buildings. Also, Hamas placed great emphasis on camouflaging the openings of the tunnels. Therefore, finding a tunnel entrance was a slow dangerous process to avoid enemy fire, avoid booby-traps and recognize the camouflage. An Israeli unit could be inside a building on the same floor as the tunnel entrance, searching for it and still be surprised by a Hamas team ‘popping out’ of the floor or wall. An Israeli unit could be in the street and suddenly be attacked from behind by a Hamas team ‘popping up’ out of the ground or shooting at it from a building the Israelis had previously searched and thought they had cleared. In one incident in Shujayia, the entrance to a tunnel was discovered only 6 days after it had been used to attack an Israeli unit and therefore the building it was in had been searched a number of times.” 

“61.   Over the years the Israelis turned a blind eye to the activities in these tunnels except when they had explicit information on the transfer of a weapons shipment through a specific tunnel. During the war in the summer the Israelis completely ignored these tunnels. Egypt on the other hand, angered by Hamas’ assistance to the Salafist Jihadi terrorists attacking Egyptian civilians and soldiers, began searching for and shutting down the exits to the tunnels on its side of the border. Over the past year and a half, with complete and free access (this is Egyptian territory) the Egyptian forces located and destroyed more than 1,800 tunnels. This was done by house to house searches in the Egyptian town of Raffa where all the tunnels have active entrances – many of them very large and impossible to hide once the right building is entered. The search was conducted without need for combat as the house owners are mostly Egyptian civilians working for profit and have no motivation to fight. Some months ago the Egyptian authorities decided that the only solution is to evict the population and raze all the houses within 500 meters of the border with Gaza and then dig a deep ditch and fill it with sea-water. There have been more recent reports that before digging the ditch they intend to widen the depopulated zone to about 1,000 meters.” 

“How does the IDF destroy the tunnels?

69. The manner of destruction depends on the type of tunnel and the result required. I will begin with the easy part – the non-cross border tunnels. 

Non-Cross-Border Tunnels 

70. As I described above, ground fighting inside Gaza resembled a deadly version of the game of ‘hide and go seek’ – Hamas fighters hid in the buildings and set off bombs hidden inside adjacent buildings or in the streets (thousands of bombs of various sizes and shapes were emplaced in residential and public buildings including Mosques and medical clinics – some were placed only when the fighting began, others were embedded permanently in the walls or floors of buildings) when Israeli troops passed near them as well as firing small-arms, RPG rockets and mortar bombs towards the Israeli troops. 

71. As noted before – non-cross-border tunnels interested the Israeli ground forces only insofar as they were being used to attack them while they searched for the cross-border tunnels. Tunnels that were considered non- cross-border merely had their entrances blown in with explosives to prevent them being used to infiltrate Hamas attack-teams behind the advancing Israelis. This sometimes proved insufficient because of the way the tunnels were built, so that the damage caused was superficial and Hamas fighters reopened them. 

72. During the summer 2014 war the Israeli air force attacked a long list of targets that included many tunnels inside Gaza. It was not used to attack cross-border tunnels. Air attacks are usually not effective in destroying entire tunnels – the depth of the tunnels means that only special bombs will reach them and their small size means that to hit them requires extremely accurate intelligence as to their exact location (this is not a finding unique to Gaza – the Americans were confounded by it in Vietnam). Therefore, unable to know the exact trace of the tunnel underground, the Israeli air force attacks tunnels by dropping bombs on the entrances. However, the damage caused is only partial and temporary – collapsing only that entrance and perhaps a very short section of tunnel next to it. The exact extent of the damage depends on the depth of the tunnel – the deeper it is, the longer the entrance-shaft and the less the damage to the tunnel beneath. Other entrances would rarely be damaged and the damaged entrance can be replaced by digging a new one within a couple of weeks. Therefore, aircraft are usually used only to attack tunnels that ground forces cannot reach, or when a partial and temporary destruction of a tunnel is deemed sufficient. Exceptional cases are tunnels used to store explosive or flammable materials. In a number of cases in Gaza, bombs dropped by the Israeli air force on the entrances of storage-tunnels filled with explosive and flammable materials set-off a chain-reaction of sympathetic explosions that destroyed the entire tunnel and its contents.” 

“74. During the summer 2014 war, the required result was total and permanent destruction of the cross-border tunnels. To do this the Israeli soldiers had to: 

1. Fight their way to the suspected locations of tunnel entrances, search those locations to find the tunnel entrance. 
2. Then they had to fight off Hamas counter-attacks while clearing the explosive booby-traps around and in the tunnel entrances or dig a new parallel entrance to avoid the booby-traps altogether. 
3. Then they searched each tunnel to map it in order to find all the branches and entrances – again having to deal in some cases with booby-traps and sometimes ‘bumping’ into Hamas fighters waiting inside the tunnels – in order to figure out where it was going. In some cases what initially looked like a cross-border tunnel turned out to be only a tactical tunnel inside Gaza.
4. After clearing and mapping each tunnel, Israeli soldiers had to manually carry several tons of explosives into it with a minimum of mechanical help like a winch for inserting it down the typically 20 to 25 meter long entrance shaft. The exact tonnage depended on the length of the tunnel, but averaged 9 to 11 tons per tunnel. 
5. Then the explosives were scattered along the entire length of all the branches of the tunnel and connected to a common detonator. The amount of explosives used was computed to be the minimum necessary to ensure destruction of the tunnel with minimal damage above ground. Since the tunnels were reinforced with concrete too small a charge would have not caused sufficient damage to destroy the tunnel. 
6. Other Israeli soldiers were sent above ground to ensure that the area above the tunnel route was clear of people. 
7. After this the explosives were fired. 

75. It should be emphasized that throughout this laborious and therefore long process (usually a few days per tunnel) the entire area around the tunnel entrance and between the tunnel entrance and Israeli territory had to be kept clear of Hamas fighters trying to attack the Israeli tunnel units either above ground or via tactical maneuver tunnels, sniping from a distance and bombarding them with mortars. 

Dr. Eado Hecht

(Ph.D. Hebrew University) Defense analyst specializing in military theory and military history. Lectures at Bar-Ilan University, Haifa University and at the IDF Command and General Staff College. Serves on the Editorial Advisory Panel of The Journal of Military Operations. Email: eadohecht@walla.com

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^[1]Indications for this are the inordinate number of armed guards and closed areas in the lower areas of the hospital and guarded remarks by locals to foreign journalists.