Subterranean Warfare

Subterranean warfare encompasses considerably more than fighting inside tunnels: underground routes can conceal forces, move people and supplies, enable escape, carry assault forces behind enemy lines, or house explosives beneath a target.[1] A useful distinction separates passages primarily intended for movement from installations intended for shelter, storage, command, or accommodation; individual installations may also form parts of a larger connected underground layout.[3] Consequently, an underground system can function simultaneously as protective infrastructure and as an operational environment affecting the battle above it.[3]

Tunnels have frequently served weaker forces seeking concealment from stronger opponents.[4] Excavation requires time, which can favor local forces already familiar with the terrain over an unfamiliar army entering the area.[1] Underground spaces offer opportunities for surprise, protected movement, and defensive survival, while complicating remote surveillance and attack.[5] In Gaza, these functions gave Hamas and other Gaza-based terrorist groups a ground-operation capability alongside rocket fire, including opportunities for ambushes, cross-border attacks, and abductions.[4]

Routine security operations against smuggling or attack tunnels differ from wartime operations against extensive underground spaces occupied by an opposing force.[3] In the latter setting, locating and destroying isolated passages may be insufficient: underground operations may need to form part of a broader ground maneuver.[3] Intelligence, mapping, communications, specialized equipment, and suitable doctrine therefore belong to the same operational problem rather than constituting separate technical tasks.[3]

Siege warfare employed tunnels both defensively and offensively: defenders concealed people and property underground, while attackers excavated beneath walls to bypass them or undermine their foundations.[6] Defenders sometimes dug counter-tunnels to find and confront the attackers.[6] Gunpowder increased the effectiveness of mining and countermining because sappers no longer had to navigate as precisely to the intended target.[6]

During World War I, opposing armies dug hundreds of tunnels, commonly called mines, beneath positions on the French front, packed them with explosives, and detonated them.[6] Individual attacks killed dozens and sometimes more than a hundred people.[6] At Messines in Belgium, British forces detonated 19 mines beneath German positions in a system described as approximately 38 meters deep; the resulting operation combined underground demolition with the capture of positions above ground.[7]

Underground fighting also featured at Okinawa in 1945.[7] During the Vietnam War, the Viet Cong used hundreds of kilometers of multilevel tunnels for living underground, hiding from American forces, and launching raids or ambushes.[6] These systems included areas associated with traps and deception as well as deeper spaces for shelter and logistics.[7] The United States established specialized units known as “Tunnel Rats” to discover tunnels and fight inside them.[6]

Gaza’s tunnel industry initially developed around Rafah, serving economic activity and smuggling, including the movement of weapons from Egypt.[4] The underground trade subsequently included civilian goods, while tunnels also became routes for attacks on Israeli forces in Gush Katif during the second intifada.[4] A BESA Center account says that after Israel’s withdrawal from Gaza, the number of smuggling tunnels grew from dozens to hundreds and that taxes imposed by the Hamas government on imports became a major revenue source.[6] A separate assessment states that closure of the Egypt–Gaza border in 2013 curtailed this trade.[8]

Direct military tunnel activity against Israel began in 2001 and developed into longer, deeper, more stable passages with increasingly ambitious purposes.[9] A booby-trapped tunnel at the Termit outpost wounded three Israeli soldiers in September 2001.[4] In June 2004, an attack on the Orhan outpost killed one soldier and wounded five; a December attack on the Joint Verification Team outpost in Rafah killed five and wounded six.[4] Israeli forces had destroyed more than 100 tunnels by June 2004, but trenching, explosives, and demolition of nearby houses had not eliminated the problem.[4]

On June 25, 2006, an assault squad emerged from a tunnel approximately 100 meters inside Israel near Kerem Shalom.[4] Two Israeli soldiers were killed, another was wounded, and Gilad Shalit was abducted.[6] Subsequent Israeli actions included demolition of 13 smuggling tunnels along the Philadelphi Route in October 2006, tunnel infrastructure near Netiv HaAsara and Kibbutz Erez in November 2007, and an entrance near the Gaza border in November 2008.[4]

According to a BESA Center analysis, after taking control of Gaza, Hamas expanded interconnected concrete bunkers and tunnels beneath residential areas, using multiple entrances and exits to support concealed movement and attacks.[6] The analysis states that openings were concealed in residences, mosques, schools, and other public buildings, allowing terrorists to emerge at different locations and return underground after attacking.[6] This method was used during Operation Cast Lead in December 2008–January 2009, after which the project expanded.[6] By 2008, the network supported offensive and defensive purposes, including protecting military infrastructure and sustaining Hamas operations during prolonged fighting.[10]

The scale and cost of individual projects varied considerably in published accounts.[4][11] One estimate described a tunnel taking approximately three months to excavate and costing about $100,000, with entrances concealed in houses or greenhouses and passages sometimes completed before use.[4] In a more elaborate example, the Jerusalem Center for Public Affairs describes a tunnel discovered near Kibbutz Ein Hashlosha on October 7, 2013, as 1.8 kilometers long and 18 meters underground, with electricity and provisions; its account gives two years of construction, 800 tons of concrete, 25,000 slabs, and an Israeli cost estimate of $10 million.[11]

Israeli forces destroyed two cross-border tunnels in November 2013 and another in March 2014.[4] During the escalation preceding Operation Protective Edge, an Israeli action against a tunnel near Rafah on July 6, 2014, killed six Hamas operatives.[4] On July 17, an attempted attack by 13 terrorists emerging near Kibbutz Sufa was foiled, followed by the start of Israel’s ground operation.[4] The combined air-and-ground campaign sought to locate and destroy tunnel entrances, and Israeli forces found and began neutralizing 21 assault tunnels within the first 24 hours of the ground invasion.[8]

The CTC account reports that the Israel Defense Forces discovered 32 offensive tunnels during the war, including 14 reaching into Israel and another two with exits within 500 meters of the border.[12] These routes were designed to move assault squads past border defenses undetected and enable surprise attacks.[12] Six tunnel-based infiltration operations took place, with Israeli forces engaged in four; eleven Israeli soldiers were killed in those clashes.[12] The July 29 attack on the Nahal Oz security post killed five Israeli soldiers and appeared intended to take hostages.[12]

On August 1, three Givati Brigade soldiers were killed, and First Lieutenant Hadar Goldin’s body was taken into a tunnel toward Rafah.[4] According to an Israeli government report, Israeli ground troops withdrew on August 5 after locating and destroying 32 cross-border assault tunnels, comprising 14 that penetrated Israeli territory and 18 unfinished routes approaching the border.[9] The passages encountered included multiple shafts, branches, and sometimes parallel routes.[4] Concrete reinforcement, internal communications, and compartments for weapons, food, and potential hostages supported sustained use and coordinated raids.[8]

The underground system also sheltered command functions, commanders, personnel, weapons, and ammunition.[12] It supported rocket operations by concealing launch sites and providing escape routes for launch teams, while communications and defensive tunnels enabled protected battlefield movement.[12] These functions complicated aerial reconnaissance, precision targeting, and efforts to locate senior operational leaders.[8] Israeli forces could be searching for entrances inside Gaza while attackers used other passages to emerge in Israel.[8]

Detection and demolition proved separate and demanding tasks.[8] Some passages reached depths of 30 meters, and knowing an entrance did not reveal the route or its exit.[8] Initial bombing failed to destroy some branches or teams waiting underground, while shortages of excavation equipment meant tunnels were handled sequentially.[8] Robots sometimes lost communications after advancing approximately 100 meters, and tunnel air pressure reduced explosive effectiveness; in some cases, destroying a kilometer of passage required as much as 16 tons of emulsion and 60 mines.[8] Entrances were routinely booby-trapped, adding to the engineering burden.[12]

Hezbollah’s underground infrastructure developed from weapons storage and personnel protection in Beirut and central Lebanon in the mid-1990s to combat positions in southern Lebanon after Israel’s withdrawal in 2000.[6] Underground positions supported rocket launches and operations against Israeli forces above ground, and investment in tunnel complexes increased after the 2006 war.[6] An Egoz Unit force fought in a Hezbollah tunnel system at Jabal Sujud in September 1996.[4] During the Second Lebanon War, Maglan forces captured a fortified dugout in a battle that killed two Israeli soldiers and five Hezbollah operatives.[4]

Operation Northern Shield, conducted in December 2018–January 2019, targeted Hezbollah tunnels crossing from Lebanon into Israel.[13] One passage near Metulla was approximately 80 feet underground, six feet wide and six feet high, and extended about 130 feet into Israeli territory.[13] A larger tunnel discovered in January 2019 was approximately 3,280 feet long, reached a depth of 260 feet, and extended 250 feet into Israel.[13] The IDF described electricity, ventilation, communications, and a railway for moving equipment and waste inside it, and announced completion of its destruction in May 2019.[13]

Geology affects comparisons between the two theaters: Gaza’s soft sandstone permits easier excavation than the harder limestone of Lebanon and the West Bank — known by its original, indigenous Jewish name of Judea and Samaria.[2] A 2025 assessment characterized Hezbollah’s underground infrastructure as more geographically limited than Gaza’s and largely known to Israeli intelligence, with most of those systems destroyed by air power within hours, days, or weeks after the campaign intensified in September 2024.[2]

By May 2021, the Gaza tunnel system, called the “metro” by Israeli officials, was central to Hamas’s warfighting concept and enabled personnel and rockets to move underground for offensive and defensive operations.[14] On May 14, an Israeli military spokesman described a 40-minute operation involving 160 aircraft, artillery, and armored units, without ground forces crossing into Gaza.[15] Israeli officials subsequently said airstrikes had destroyed approximately 100 kilometers of tunnels over several days.[14]

The network encountered during the war that began on October 7, 2023, linked military facilities and headquarters to thousands of shafts serving urban combat positions and rocket-launching locations.[2] A 2025 estimate placed its initial length at 500–600 kilometers.[2] A separate estimate published in January 2024 put the system at 560–720 kilometers with 5,700 shafts, substantially above an earlier estimate exceeding 400 kilometers.[16] Israeli forces used mapping technologies, small drones, and dogs in their investigations, and seawater flooding was also reported.[16]

Reported underground facilities included routes for moving rockets, weapons and ammunition storage, food, generators, and other supplies, as well as spaces for dispersing personnel and holding hostages.[17] Other descriptions identified main and bypass routes, passages associated with motorcycles or boat access, and explosive charges, trapdoors, and other booby traps.[18] These accounts portrayed a system whose functions extended beyond infiltration to sustained logistics, concealment, and underground habitation.[17][18]

Yaakov Ayish and Mark Fox argue in Sapir Journal that Israeli forces encountered an interconnected network concentrating command and control, production, communications, and logistics underground, rather than merely isolated shafts.[19] They describe a shift from concentrating on entrances toward simultaneous surface and underground operations, including fighting inside the network and targeting important underground centers.[19] Clearing remained incomplete when the 2025 assessment was written, reflecting the danger of operations and the quantities of explosives and specialized equipment required.[2]

Detecting excavation differs from locating a completed, unused tunnel.[1] Construction noise can be monitored through underground microphones known as geophones, whereas dormant passages may require techniques that examine underground spaces through sound waves, infrared radiation, or microgravity measurements.[1] Other approaches have included ground-penetrating radar, fiber-optic sensors, and magnetic or seismologic systems.[4][8] Background noise, terrain, geology, weather, and soil moisture affect performance, and techniques useful for geological mapping may fail to resolve small voids at substantial depth.[1][4]

Israeli engineering efforts against Gaza tunnels date to at least 1990.[4] A 2006 State Comptroller warning identified the intensification of smuggling tunnels as a strategic threat, and three systems under development had not succeeded by 2007.[4] Later technological work brought together Elbit Systems, the Geophysical Institute of Israel, and the Ministry of Defense’s weapons and technological infrastructure administration to develop sensor-based detection; experimental deployment began in April 2014, followed by operational deployment.[20]

In 2016, a system using sensitive radar and other sensors helped direct engineers to a concrete-supported tunnel almost 30 meters deep.[21] Its first successful detection did not establish a comprehensive solution, and development continued.[21] By 2017, a tunnel-detection laboratory near the Gaza border combined engineers, geologists, intelligence specialists, and combat-engineering officers to process data, including acoustic information, and identify digging before it reached Israeli communities.[22] Israel was also installing an underground border wall.[22]

A tunnel discovered near Kerem Shalom in 2018 illustrated the complexity of routes around border infrastructure: the 1.5-kilometer passage ran beneath the goods-transfer checkpoint, extended into Egypt, and included approximately 180 meters in Israeli territory.[23] Locating a passage did not by itself provide a clear view of its complete underground layout.[23] Destroying an entrance or several shafts could leave other sections usable, while bombing shafts could make subsequent detection harder.[6][4]

Depth and layout also affect operations inside tunnels.[18] Reported Gaza examples distinguished shallow routes around ten meters deep linked to rocket-launch shafts, intermediate routes around 20–30 meters used for ammunition, logistics, and personnel, and deeper spaces reaching 75 meters associated with command centers.[18] Underground conditions restrict electromagnetic communications with robots, while stairs, slopes, and zigzag passages can obstruct movement or disrupt links.[18] Generators require air, providing another constraint on the placement of underground facilities.[18]

The IDF’s Yahalom engineering unit developed a specialist company, variously rendered Samoor or Samur, in the early 2000s to address hidden weapons caches and tunnels.[4][24] After the 2014 war, the army expanded Yahalom and its subterranean capability, added tunnel-like training facilities, and sought robots for reconnaissance, mapping, and explosive searches.[24] By 2018, training had broadened from a predominantly special-forces task to preparing every infantry soldier to deal with tunnels.[25] Mock passages beneath military bases reproduced concealed entrances and side spaces that complicate observation.[25]

The preferred objective was often to handle tunnels from above ground while preparing for situations requiring entry.[25] Israeli forces generally sought to isolate a detected area and identify additional shafts and branches before demolition, avoiding entry unless necessary.[4] Methods described during Operation Protective Edge included aerial bombardment, water, and liquid explosives.[4] Combat engineers’ broader responsibilities—explosives, mine clearance, breaching, fortifications, bridges, and heavy equipment—provided the institutional setting for developing tunnel detection and demolition capabilities.[26]

An operational framework for underground threats separates intelligence collection, identification of the underground locality, temporary neutralization, and a final decision to control, hold, destroy, or otherwise resolve it according to the mission.[3] Navigation, communication, disorientation, traps, and the opposing force all shape that process.[3] Underground maneuver therefore requires coordination with surface operations rather than treatment as an entirely separate campaign.[3]

International cooperation also became part of Israel’s response.[17] From fiscal years 2016 through 2023, the United States Congress appropriated $320 million for U.S.–Israeli collaboration on detecting, mapping, and neutralizing tunnels.[17] This effort accompanied Israeli investment in specialized formations, training environments, sensors, and multidisciplinary analysis.[24][22]

Urban and subterranean terrain can reduce guerrilla forces’ exposure to remote detection and fire technologies, offering offensive opportunities and particularly strong defensive potential against technologically sophisticated forces.[5] A study of terrain in eight IDF engagements since the late 1960s emphasized the importance of terrain analysis and called for further semiquantitative research into when terrain has a significant relative effect on combat.[5] Concealed shafts in built-up or ruined areas can enable small units to emerge, ambush, fire rocket-propelled grenades, place explosive devices, and disappear underground.[2] In a 2025 INSS assessment, Azar Gat called the underground “the most consequential factor shaping the limitations of warfare in the Gaza Strip.”[2]

A Jerusalem Center for Public Affairs analysis argues that tunnel-based rocket launchers can reduce the advantages of air power by appearing briefly to fire before returning to concealment.[27] Underground mobility and shelter likewise complicate attempts to identify launch locations, disrupt resupply, or target command personnel.[12][8] The combination of extensive underground construction and urban terrain adds difficulties beyond those posed by either environment alone.[28]

The presence of hostages introduces an additional constraint on clearing and demolition.[29] Lethal methods against underground spaces can endanger hostages inside and civilians above or nearby, while attacks on underground infrastructure can affect buildings at the surface.[17][28] An Israeli government report characterized military infrastructure embedded in densely populated civilian surroundings as creating operational, legal, and ethical challenges.[9] The underground problem is therefore not simply one of discovering a hidden route, but of deciding how to act against it within a wider battlefield containing troops, buildings, and civilians.[3][9]

The network’s precise extent and the effects of attacks on it remain difficult to establish independently: Hamas’s 2021 claim of 311 miles of tunnels was a claim rather than a verified measurement, and published estimates from different dates are not interchangeable.[17][16] Information used to depict particular underground facilities included media reporting that could not be independently verified, while assessments of the May 2021 strikes initially remained provisional.[17][14]

The Israeli response before the 2014 war also generated a substantive debate: critics viewed the scale of the threat as evidence of strategic failure warranting inquiry, while substantial detection efforts had nevertheless been undertaken without solving the problem.[4] A 2017 State Comptroller report criticized the defense establishment’s response as slow and ineffective, with parts of its findings classified.[23] The associated resource question was whether greater tunnel-defense investment should take precedence over other offensive and defensive requirements, rather than whether tunnels represented the country’s sole strategic threat.[4]