An Israeli soldier looks at a tunnel exposed by the Israeli military near Kibbutz Ein Hashlosha, just outside the southern Gaza Strip, on Oct. 13. Israeli officials say Hamas operates a network of what it calls “terror tunnels.” The U.S. military has expressed concern about the use of tunnels by potential adversaries, and is looking for new equipment that could help. (Amir Cohen/Reuters)

The Israeli military launched a ground offensive late Thursday, targeting in part an expansive network of tunnels in the Gaza Strip used by armed fighters with the Hamas organization. The fighting over the weekend killed more than 100 Palestinians and 13 Israeli soldiers, and the tunnels were referenced directly by President Obama on Monday.

“As I’ve said many times, Israel has a right to defend itself against rocket and tunnel attacks from Hamas,” Obama said. “And as a result of its operations, Israel has already done significant damage to Hamas’s terrorist infrastructure in Gaza.”

A video released Monday by the Israel Defense Forces purportedly shows Hamas militants taken down by the Israeli military after entering the land through tunnels. (Israel Defense Forces)

As noted on The Washington Post’s Morning Mix blog today, the network of tunnels in Gaza is elaborate. In one example, Israeli soldiers found one last fall that was 1.5 miles long, 66 feet deep and equipped with electricity and provisions that could last occupants several months. Israeli officials estimated that it required $10 million and 800 tons of concrete to build.

Tunnel warfare is anything but new, however. Its history goes back centuries, with tunnels dug in Syria, Iraq, Egypt, Afghanistan, and North Korea, among other locations. Closer to home, they’re frequently used to smuggle drugs and weapons into the United States from Mexico.

As pointed out in this story I wrote for Foreign Policy magazine, the U.S. military believes the use of tunnels by potential adversaries is on the rise, and has launched an effort to find new equipment and training methods to prepare for it.

“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),” U.S. military officials said in message posted to industry in December. “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 message, published by the U.S. Army, said the Pentagon needs to have specialized personnel available for tunnel warfare, or at least incorporate subterranean warfare into military training. The service was interested in equipment that can map out underground environments when GPS signals were not available, radios that can work underground, breaching gear that can blow holes into walls, breathing devices for when there is limited oxygen, and equipment that will allow soldiers to see in the dark.