The Author is Former Director General of Information Systems and A Special Forces Veteran, Indian Army

Discovery of cross-border tunnels along the India-Pakistan border in Jammu and Kashmir (J&K), Punjab and Rajasthan have been a periodic affair over the years. Many of these were reported in these columns before. Between 2001 and 2016, India has discovered at least eight tunnels originating from across the border along Pakistan, at an average of one every two years. Only one of these was suspected to have been dug for drug running, while the others are linked to infiltration operations.

In August 2020, the Border Security Force (BSF) detected a tunnel, originating from Pakistan, just beneath the Indo-Pak International Border (IB) fence in Jammu. The tunnel, about 50 metres from the border fence on the Indian side, was located by a BSF patrol in the Galar area of Samba sector in Jammu. 8-10 plastic sandbags stuffed in the tunnel's mouth had Pakistani markings.

Between 2001 and 2016, India has discovered at least eight tunnels originating from across the border along Pakistan, at an average of one every two years

According to news reports of January 8, 2023 the BSF unearthed at least five underground tunnels in the stretch of about 192 km in the Jammu front of the India-Pakistan IB. Subsequently on January 23, another such structure was found beneath the IB in Hiranagar sector, the 10th in the past decade. The tunnel detected in Jammu and Kashmir's Kathua district in the Hiranagar sector was a 150-meter-long underground tunnel, with 25 to 30 feet depth, constructed by Pakistan to facilitate the infiltration of terrorists for subversive activities.

Above are only a few examples but it is relevant to note that since January 2023, the BSF has been deploying drone-mounted ground penetrating radars to check tunnels along the border with Pakistan. These indigenous radar-mounted drones are capable of detecting cross-border tunnels for infiltrating terrorists, as well as smuggling narcotics, arms and ammunition.

Somehow the attention for cross-border tunnels has always been on India's western flank, despite the fact that almost the same quantity of narcotics enter India from our eastern flank, as from the west. On January 25, 2025, the discovery of a tunnel on the India-Myanmar border stunned officials because a truck was used through it to smuggle narcotics. 32 kgs of methamphetamine tablets were seized from the truck costing about ₹32 crore. According to the Finance Ministry, the drugs were being transported in an Ashok Leyland truck through the cave.

On April 26, 2017, the BSF found an 80-feet long cross-border tunnel on the India-Bangladesh border, which the BSF believes was being built by cattle smugglers to minimise the risk of detection. The tunnel, located in Chopra region of West Bengal's North Dinajpur district, was the second instance of the BSF detecting a trans-border tunnel on the Bangladesh border. In early March, the guards had detected a tunnel at the depth of 20-25 feet in Meghalaya about 200 metres from the border fence.

Since January 2023, the BSF has been deploying drone-mounted ground penetrating radars to check tunnels along the border with Pakistan

On July 17, 2024, a tunnel 40-meter in length, lined with brick and concrete, 8-10 feet deep, 5-6 feet high, and 4-5 feet wide was uncovered beneath the residence of an alleged counterfeit gold idol dealer in West Bengal. On one end, the tunnel opened in the basement room of the single-story house of the accused Saddam Sardar, and on the other side linked to a canal connected to the Matla River in the Sunderbans which lies on the India-Bangladesh border.

In a recent case on January 26, 2025, the BSF found three large underground bunkers used for smuggling narcotics on India-Bangladesh border; stockpiled with ₹1.4 crore worth of the Codeine-based cough syrup 'Phensedyl' in Majhdia, an area in Nadia barely two-km from the Bangladesh border. Tunnels and underground bunker on the India-Bangladesh border need to be viewed with serious concern, due to the regime change and rise of radicalisation in Bangladesh. BSF authorities said in a statement that the three rectangular bunkers, each 15 feet deep built with brick walls and metallic covers, and equipped with locking mechanisms, contained 62,200 bottles of Phensedyl. A fourth bunker under construction was found lined with metal sheets.

The question is how serious are we about such threats along our borders, especially when 24x7 satellite cover along all our land borders is still 8-10 years away? As per the media, the government has been looking for two key technologies to cope with the menace of infiltration and smuggling: one, tunnel detection system, and; two, gunshot detection system. In January 2017, testing for ruggedness was in progress for a Ground Penetration Radar (GPR) at 920 MHz developed by the National Centre for Excellence in Technology for Internal Security (NCETIS) at IIT-B in collaboration with other IITs, with field trials in multiple terrains and conditions following. This initial project was for landmine detection, to which the additional requirement of tunnel detection was added by the BSF. The MHA had also invited vendors, manufacturers, distributors and experts to share recommendations and product details, if any, in addition to looking at foreign collaboration. The BSF was also looking for a three-tier gunshot detection system that can provide an alert one second after an enemy shot has been fired from 300-1,200m: one, standalone detection system, vehicle mounted system and weapon mounted system.

On January 25, 2025, the discovery of a tunnel on the India-Myanmar border stunned officials because a truck was used through it to smuggle narcotics

Looking at technologies being used worldwide to detect underground tunnels, the Synchronized Electromagnetic Gradiometer uses the enhanced conductivity associated with tunnels, as compared to the surrounding medium, to detect the tunnels. A low-frequency electromagnetic (EM) signal is used to illuminate the area of interest. This signal, in turn, induces current flow in any conductors within the tunnel that generate secondary EM fields observable at a distance from the tunnel. The magnitude of the secondary wave can be orders of magnitude less than the illuminating signal.

An efficient detection system has been achieved by using a gradiometer design that suppresses the illuminating signal by more than 70 dB while maximising the secondary signal with a narrow bandwidth (BW = 1 Hz) synchronised receiver. Once all of the measured waves are recorded, these are charted on a computer through a process called seismic refraction tomography; locating the tunnel indicated by the abnormalities in the chart.

In a recent case on January 26, 2025, the BSF found three large underground bunkers used for smuggling narcotics on India-Bangladesh border

Over the past several decades, many geophysical methods have been proposed to detect underground tunnels and void spaces, such as electromagnetic (EM), gravity, ground-penetrating radar (GPR), and seismic refraction, diffraction, and surface-wave methods. GPR technology uses radio waves to detect buried or otherwise concealed subsurface objects. It can detect both metallic and non-metallic components, making it useful in a variety of environments and applications. GPRS uses the ImpulseRadar PinPointR GPR Scanner for utility locating. Acoustic sensors buried in the ground listen for the sounds and vibrations of underground work being done. That's largely how modern tunnels are detected.

At the same time, LIDAR is capable of scanning the tunnel in three dimensions, as well as constructing a three-dimensional spatial image in real time. LiDAR can effectively provide the tunnel safety index, when used in tunnel detection. Similarly, any sonar returns are bandpass filtered so only an acoustic frequency difference heterodyne can pass through. The existence of a tunnel is revealed by the return of acoustic frequency difference heterodynes all coming from a more-or-less horizontal line of phase-delayed sources and directions. Detection of tunnels and bunkers below human-made structures through remote sensing methods commonly use instruments on satellites, unmanned aerial vehicles and aircraft to provide datasets to analyses.

Finally, unlike most foreign countries, our international borders are manned by different forces, which are operating under different ministries. But looking at the threat envelope, we need to take immediate steps to cover all our land borders with the best detection technologies in the earliest time frame. Rather than leaving the issue to be dealt with separately by the MHA and the Ministry of Defence (MoD), the government needs to constitute a central group to come up with an action plan to be executed in a time-bound manner.