A few US Army units are training and preparing soldiers to fight in tunnel networks in case the US has to carry out a land invasion of North Korea (DPRK). In the event of an all-out war, US soldiers will need to fight in tunnels inside the country.

North Korea is known to have a vast network of underground tunnels that number in the thousands where the leadership, that makes up the bulk of the rogue nation's top brass, is likely to be held and guarded in case the US decides to invade the country. The country's bombs, including their nuclear arsenal and cache of biological weapons, are also likely to be held in tunnels, according to a report in Popular Mechanics (PM).

PM reported that North Korea has between 6,000-8,000 tunnel facilities, with some of them having stockpiles of chemical weapons. The quantity of the chemical weapons estimated by South Korean intelligence stands at around 2,500 to 5,000 metric tons, including hydrogen cyanide and mustard gas. Nerve agents like sarin, soman and VX are also expected to be part of these toxic stockpiles.

In a four-day exercise called "Warrior Strike IX", soldiers from the 1st Battalion, 5th Cavalry regiment and 1st Cavalry Division practised routines on how to breach and enter tunnel complexes in their army camp in South Korea. The training was carried out with the soldiers wearing chemical protective masks and night vision goggles to help them navigate dark tunnels.

The training also included soldiers moving through a half-mile long U-shaped tunnel using their Mobile Ad Hoc Networking Unit system, which is also called MPU5. The radio makes use of a peer-to-peer Wi-Fi that can communicate from deep underground to the surface. It is based on Android and can relay video, voice and text, much like a smartphone, noted the report.

Boots that the soldiers wore during this exercise also contained smart tracking devices that enabled the command to keep a track of every soldier's movement underground and make sure they were out of sight.

The report mentions that in the event of a war, it is highly likely that the South Korean troops will do most of the fighting, but there might be cases where US soldiers have to join in. This training was carried out to make sure the American troops are well-prepared to fight in all situations, even if it involves fighting deep underground.