Israel will use novel “sponge bombs” as it fights through the network of Hamas tunnels under Gaza.
The Israel Defense Forces (IDF) has been testing the chemical bombs, which contain no explosives but are used to seal off gaps or tunnel entrances from which fighters may emerge.
The IDF has not commented on the use of the so-called “sponge bombs”, which create a sudden explosion of foam that rapidly expands and then hardens.
Its soldiers were seen deploying the devices during exercises in 2021. The army has set up a mock tunnel system at the Tze’Elim army base near the border with Gaza.
Troops face a bloody battle through the tunnels known as the “Gaza Metro” when they launch their expected ground invasion. The network is thought to be hundreds of miles long and dense with traps.
It is where Hamas has taken many of the 200 hostages and where its leaders will hope to survive the coming war.
Israeli soldiers blinded mishandling new “bomb”
The “sponge bomb” would prevent soldiers being ambushed as they move further into the network, sealing off gaps through which Hamas could attack.
Contained in a sturdy plastic container, the specialist devices have a metal partition in the middle separating two liquids. Once this barrier is extracted, the compounds mix as the soldier positions the “bomb” or throws it further ahead.
Specialised teams in the IDF’s engineering corps have been grouped into tunnel reconnaissance units and equipped with ground and aerial sensors, ground penetrating radar and special drilling systems to locate tunnels.
They have also been issued with special equipment to see when underground.
Standard issue night vision goggles need an element of ambient light to work effectively, but with all natural light blocked out when moving underground, troops will rely on thermal technology to see in the total darkness.
Novel radios, optimised for working in the extreme conditions experienced underground, have also been developed.
There are potential complications with the underground arsenal, however. The “sponge bomb” – technically a liquid emulsion – is hazardous to work with, and some Israeli soldiers have lost their sight through mishandling the mixture.
Israel may also use robots and drones to help when navigating the tunnels – but so far, there have been difficulties operating these underground.
Some of the robots will be controlled by wires spooling out of the rear of the device. Others will rely on standard radio waves, but will need a series of repeater nodes to be dropped off en route as radio signals degrade quickly underground.
Micro-drones for reconnaissance, capable of being held in the palm of a hand, may also be used but will similarly suffer as the radio signal weakens.
The Israel-based Roboteam technology company has developed IRIS, a small, throwable drone that can be driven on large wheels via remote control.
Known by special forces as a “throwbot”, it relays images back to a controller, operating the device from a position of safety.
Some devices can have weapons attached so that if enemy combatants are seen, the controller can detonate explosives.
Alongside the IRIS, it has developed the MTGR, a “micro tactical ground robot” that can climb stairs and is designed to be operated by soldiers in buildings and caves.
John Spencer, a former US major who chairs urban warfare studies at the Modern War Institute at West Point, says subterranean fighting is “more like fighting underwater than fighting in buildings”.
“Nothing that is used on the surface works in the same way or with the same efficiency underground.
“Specialised equipment is needed to see, to breathe, to navigate, to map the space, to communicate and to deploy lethal means.”
Targeting the tunnels risks civilian lives
Hamas has integrated underground warfare into its overall military strategy.
Tunnels, some started decades ago, are no longer just places of refuge or concealment, but are integral parts of a wider plan to prepare the ground for ambushing Israeli forces above.
Many stretch under civilian structures, with entry and exit points in dwellings and other non-military buildings, making it extremely difficult for Israel to attack them without inviting international condemnation.
A “standard” tunnel is about 2m high and 1m wide, which enables them to be built quickly. They are sometimes reinforced with concrete and metal but are not especially sophisticated.
Others however, have power, water and ventilation and are used for command centres and rest stations, weapons storage, infiltration into Israel and routes to secret rocket launching sites.
In some parts there is even thought to be a small rail system for the transportation of weapons and building equipment.
The last major attempt to destroy the system was in 2014’s Operation Protective Edge, but the network has been rebuilt since.
Military commanders in the IDF must decide if they want to render the structures useless, by pouring in concrete for example, as they did with the tunnels dug by Hezbollah in the north of the country.
Alternatively, they may need to keep the structures intact, clearing out Hamas fighters as they move through the system searching for the estimated hostages. The “normal” military responses to tunnels, of using explosives to destroy them or flooding to render them useless, is probably not practical.
