Israel's Major Challenge in Gaza: 'The Metro'

When Hamas released two elderly hostages last week, one of them described being led miles through a "spider's web of tunnels" that eventually led to a large hall, per the Guardian. It's no surprise: The militant group is known to maintain a labyrinth of tunnels beneath Gaza nicknamed "the Metro" by Israeli defense officials. The tunnels pose an immense military challenge, in part because their true extent isn't known, and they may help explain the delay in a wide-scale ground invasion. Coverage:

• Expansion: Tunnels beneath Gaza have existed for decades, but the New York Times explains that they've been greatly expanded since Israel tightened its blockade of Gaza in 2007 and Hamas gained control of the enclave. By some estimates, Hamas has about 300 miles of tunnels, many of them shored up with concrete and iron to withstand bombardments. Last week, Israel destroyed a tunnel beneath a beach designed to allow Hamas to attack by sea, a whole new front of this type of warfare.

• Types: The Guardian says the tunnels serve different purposes: Some go into Egypt to smuggle weapons and other materials; some are "commercial" and used for smuggling black-market goods in and out, from which Hamas takes a cut of revenue; others are for military raids into Israel. They vary in sophistication, but Hamas engineers have gotten more adept over the years in building them to sustain attacks and maintain ventilation.
• Blame game: The Times notes that Hamas stores military weapons and material in tunnels beneath hospitals and other locations, which some argue makes the militant group responsible under international law for civilian deaths from Israeli airstrikes. At the same time, critics, including UN chief Antonio Guterres, accuse Israel of violating international law because of bombardments that are deemed too indiscriminate.
• The challenge: Tunnel warfare is brutal, for obvious reasons. "I usually say it's like walking down the street waiting to get punched in the face," John Spencer, a retired US Army major and the chair of urban warfare studies at the Modern War Institute at West Point, tells the AP in an explainer. Booby traps are easy to set for invading troops, as are ambushes in cramped quarters.
• Challenge, II: In a separate analysis at the institute's website, Spencer details more of the hazards. Among other things, a "weapon fired in compact spaces of tunnels, even a rifle, can produce a concussive effect that can physically harm the firer," he writes. "A single defender can hold a narrow tunnel against a much superior force." Plus, it can be "impossible simply to see" and "in some cases, it can be impossible to breathe without oxygen tanks."
• A video: Hamas released a video earlier this month that provides a sense of their military use. The clip shows fighters emerging from tunnels in a military exercise and capturing mock Israeli soldiers and tanks. "This is what awaits you when you enter Gaza," it says at the end.

(More Israel-Hamas war stories.)