This recent resurgence in subterranean warfare is just one of the reasons why embracing urban warfare in megacities is a bad idea:
Subterranean warfare is not new. From Assyrian forces’ tunneling in the 9th century B.C. to sieges of the medieval era to the Vietnam War, underground terrain has been part of the battlefield. But it’s seeing a resurgence, as the Aleppo tunnel bombs, the Israel-Gaza conflict and even more recent examples from the battle for Mosul, Iraq, make clear. Yet, despite the increasing threat posed by subterranean warfare, the U.S. Army remains largely unprepared—in terms of doctrine, training and equipment—for this environment.
This is certainly a skill set we should have in the ground force arsenal. But this should be pursued in the context of limiting our objectives in urban areas:
We need to identify the key terrain in any particular city and match our operations to our objectives for the campaign. I'm especially speaking of a conventional war where the enemy army in the field is the real objective and a deadly and time-consuming city fight is a fatal distraction.
For underground operations, having drones or robots would certainly be a good idea to secure the perhaps limited areas in a megacity that we need to control to win the campaign.
Or to attack the enemy in the rest of the city.
But assuming we get the capability, I'm with Army Techniques Publication 3-21.51: Subterranean Operations, “Entering and fighting in a subterranean environment is extremely high risk and should be avoided whenever possible."
Have the capability. But while the subterranean mission can't be avoided, for God's sake don't eagerly embrace the mission and seek more of those missions than needed to accomplish the campaign mission.
