Subterranean Showdown: IDF’s ‘Sponge Bombs’ to Outsmart Hamas Tunnels

Robots and Drones Enter the Battlefield to Conquer Hamas' Hidden Labyrinth.

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Girish Linganna
Girish Linganna
Girish Linganna is a Defence & Aerospace analyst and is the Director of ADD Engineering Components (India) Pvt Ltd, a subsidiary of ADD Engineering GmbH, Germany with manufacturing units in Russia. He is Consulting Editor Industry and Defense at Frontier India.

When the predicted land invasion of Gaza by the Israel Defence Forces (IDF) begins, the troops will likely face difficult combat within the vast and puzzling network of underground tunnels established by Hamas around 15 years ago and known as the “Gaza Metro.”

This labyrinthine network believed to span hundreds of miles and heavily laden with traps, serves as a storehouse of rockets and ammunition caches and as a covert passageway for the movement of militants to avoid detection. But Israel now plans to deploy innovative ‘sponge bombs’ to navigate the intricate network of Hamas tunnels beneath Gaza.

Labyrinthine Tunnel Network

In these tunnels, Hamas reportedly holds many of the 200 hostages it took in the October wildcat attacks on Israeli communities and the hideout where its leaders intend to seek refuge during the impending storming of its militant network by the Israeli forces in an all-out ground offensive.

These tunnels, some initiated decades ago, now serve as more than shelters or hidey holes. They are integral components of a broader strategy to prepare the ground for ambushing Israeli forces above ground. Many of these tunnels extend beneath civilian structures, featuring entry and exit points in residential and non-military buildings. This makes it exceptionally challenging for Israel to target them without risking international condemnation.

A ‘standard’ tunnel typically has dimensions of about 2 metres in height and 1 metre in width, allowing for rapid construction. While some tunnels are reinforced with concrete and metal, they are not particularly sophisticated in design. On the other hand, some tunnels are equipped with amenities like power, water and ventilation systems. These serve as command centres, rest areas, weapons storage facilities, infiltration routes into Israel, and pathways to concealed rocket launch sites. In certain sections, there is even a believed presence of a small rail system for transporting weapons and construction materials.

The most recent significant effort to dismantle this network occurred during the 2014′ Operation Protective Edge‘. However, the tunnel system has been reconstructed and expanded since then.

The ‘Sponge Bomb’ Solution

These innovative chemical devices—the ‘Sponge Bombs’—developed by the IDF, which do not contain explosives, generate a foam explosion capable of sealing off openings and tunnel entrances to prevent enemy fighters from emerging.

The IDF has not officially commented on using these ‘sponge bombs’, which create an explosion of foam that rapidly expands and solidifies. But Israeli soldiers were observed using these devices during exercises in 2021, with a mock tunnel system set up at the Tze’elim army base in the Negev desert near the Gaza border.

How the ‘Sponge Bomb’ Works

The ‘sponge bomb’ is designed to prevent soldiers from being ambushed as they advance into the tunnel network, effectively sealing off openings that Hamas could exploit for attacks. These specialised devices are enclosed in a plastic container and consist of two separate liquids divided by a metal partition. When this barrier is removed, the compounds mix as the soldier places the ‘bomb’, or throws it further ahead.

The IDF’s engineering corps has formed tunnel reconnaissance units equipped with ground and aerial sensors, ground-penetrating radar and special drilling systems to locate the tunnels. Additionally, they have received special equipment to enable vision underground. Standard issue night vision goggles require some ambient light to function effectively. But, while moving through tunnels without natural light, the troops will rely on thermal technology to ‘see’ in complete darkness. Additionally, new radios designed for use in the extreme conditions below ground have been created.

Mishandling Causes Blindness

However, there are certain challenges associated with the underground arsenal. The ‘sponge bomb’, technically a liquid emulsion, poses risks during handling, and there have been cases of Israeli soldiers losing their vision due to mishandling the mixture. So, Israel may deploy robots and drones to assist in navigating the tunnels, but operating such technology underground has proved challenging.

Some of these robots will be guided by cables spooling from the back of the device, while others will rely on standard radio waves. However, a network of repeater nodes will be necessary to extend the radio signal as it degrades quickly in underground environments. Repeater nodes are devices, or components, in a network that receive, amplify and retransmit signals to extend the range and coverage of the network. They are commonly used in telecommunications and wireless communication to boost signals and overcome signal attenuation or interference.

Micro-Drones & ‘Throwbots’

Additionally, micro-drones designed for surveillance, compact enough to fit in the palm of a hand, might be used, although they are susceptible to signal degradation in underground conditions. Roboteam, an Israeli technology company, has developed IRIS—a small, throwable drone that can be remotely operated and moves on large wheels. This type of drone is designed to be thrown into specific locations and then operated to explore or perform tasks using its wheels and remote-control capabilities.

Referred to as a ‘throwbot’ by the special forces, the large-wheeled IRIS drone can be thrown into specific locations and remotely controlled to relay images back to an operator from a safe position. Some versions of these devices can also be armed with explosives if enemy combatants are detected. In addition to IRIS, another development is the ‘Micro-Tactical Ground Robot’ (MTGR), capable of climbing stairs and intended for use by soldiers in buildings and caves.

Subterranean Environs Combat

Hamas has incorporated underground warfare into its overall military strategy.

According to John Spencer, a former US major who leads Urban Warfare Studies at the Modern War Institute at West Point, ‘Combat in Subterranean Environments’ is more akin to underwater warfare than traditional building-based warfare. Equipment designed for surface use is not effective in underground environments. Specialised tools are required for such tasks as visibility, respiration, navigation, mapping, communication and deploying lethal measures in subterranean settings.

The IDF’s military commanders face a tough decision of whether to incapacitate the tunnels, possibly by filling them with concrete—a method used in dealing with tunnels dug by Hezbollah in the northern part of the country. Alternatively, they may need to maintain the tunnels in an operational state while clearing out Hamas fighters—an even tougher proposition—as they navigate the system in search of estimated hostages. The conventional military responses of using explosives to destroy the tunnels or flooding to make them inoperative are likely not practical in this context.


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