Subterranean warfare
History: Subterranean warfare was occasionally carried out during World War II. Examples are the defense of the Adzhimushkay quarry, or the use of the Odessa Catacombs during guerilla warfare by Soviet partisans.
In 21st century the issue of readiness to subterranean warfare was raised before the U.S. military in view of Palestinian tunnel warfare in the Gaza Strip. A December 11, 2013 request for information entitled "Technologies to enhance warfighter capabilities in subterranean environments" states in part:

In an effort to defeat United States (US) intelligence and weapons technologies and to gain tactical and operational advantages both Military and irregular threats have begun relocating, and redeploying functions into subterranean operational environments (SbT OE). The growing use of tunnels and underground facilities (UGF) by military and irregular forces to gain a tactical advantage is becoming more sophisticated and increasingly effective, making the likelihood of US Forces encountering military-purposed subterranean structures on future battlefields high. The Middle East is full of ancient and modern underground systems that can be used as assets for the enemy forces. In the US, both the northern and southern borders of the nation have had tunnels discovered connecting the US to Canada and Mexico being used by criminal elements for human smuggling, drug running, and other illegal activities. 

Director Robert Ashley of the Defense Intelligence Agency stated in 2018 that the United States Department of Defense is considering making "underground" a new domain, in anticipation of a future increase in urban warfare.

2023 Israel–Hamas war: Yehuda Kfir, who formerly led the underground warfare group in the Israel Defense Forces’ Technological and Logistics Directorate, described Israel's main strategy to destroy Hamas' extensive tunnel and underground facility network as "destroying infrastructure and buildings above ground in order to get to what’s underneath." Israel's techniques for destroying and/or sealing underground infrastructure included the use of sponge bombs, air strikes including the use of bunker buster munitions, and flooding them with seawater.
Daphne Richemond-Barak, the author of “Underground Warfare,” wrote in Foreign Policy magazine: “Never in the history of tunnel warfare has a defender been able to spend months in such confined spaces. The digging itself, the innovative ways Hamas has made use of the tunnels and the group’s survival underground for this long have been unprecedented.” A 2024 Royal United Services Institute report notes that Hamas utilizes two distinct types of tunnels: deep, sophisticated ones for senior leaders and shallower variants for lower-level operatives. The IDF initially focused on securing territory before undertaking tunnel inspections, a strategy that inadvertently allowed Hamas to stage underground ambushes. Based on interviews with Israeli commanders, the report concluded that effective counter-tunnel operations require integrated surface and subterranean combat strategies while mitigating the risk of friendly fire.

See also: Military engineering
Trench warfare
Tunnel warfare
Underground construction


== References ==