The sight of 13 Hamas terrorists deployed on the Israeli side of the border, a 10-minute march from Kibbutz Sufa on Thursday morning, probably tipped the scales, after 10 days of aerial war, in favor of a ground operation. But addressing the tunnel threat, which Israel’s technology has yet to credibly counter, is only one part of the mission launched Thursday night. The other aspect is to perform that which was not achieved from the air – thinning Hamas’ ranks, depleting its rockets stores and, most significantly, squeezing the Islamist organization so that it comes back to the table with more reasonable demands.

The soldiers and commanders on the western side of the border, inside the Strip, though, cannot consider the application of pressure and the nature of negotiations among their goals. They need concrete aims.

The first and likely most significant is the subterranean threat. Israel could have woken up Thursday to an entire kibbutz under siege. Haim Yellin, the head of the Eshkol Regional Council told the Times of Israel, standing outside a tunnel discovered several months ago, that many residents in the region are so scarred by the prospect of a tunnel attack that they hear the phantom scratching of shovels when they close their eyes at night.

A picture released by the Israeli Defense Forces shows weapons found inside a tunnel near Kibbutz Sufa in the Israeli Gaza border on July 17, 2014 (photo credit: IDF Spokesperson's office/Flash90)

A picture released by the Israeli Defense Forces shows weapons found inside a tunnel near Kibbutz Sufa in the Israeli Gaza border on July 17, 2014 (photo credit: IDF Spokesperson’s office/Flash90)

Unlike the current rocket threat, which has been largely defanged by Iron Dome and early warning systems, the ancient threat of tunnels has no technological solution as yet. “We have no advantage in the underground realm,” said Brig. Gen. (res) Moshe Sheli, the former commander of the IDF’s combat engineering corps. On the ground, in the air, in the sea, he continued, technology offers the Israeli army a distinct edge. Underground, Israel employs a variety of means “but they don’t give us a dramatic advantage, and that’s why this is such a hard challenge to crack,” he said.

Maj. Gen. (res) Israel Ziv, a former commander of the Gaza division and an officer who has argued against the re-occupation of Gaza, said Thursday that operating on the ground on the Gazan side of the border allows access to the entrance of a tunnel. “Around it there is a whole system,” he said. “Energy, oxygen, logistics – once you control the ground, you can fight in a more efficient way.”

Some of the offensive tunnels take more than a year to build. They are re-enforced with several hundred tons of concrete. The digging, a former Southern Command geologist said when examining the 1700-meter tunnel discovered last October, entailed the removal of 3,400 cubic meters of earth. Israel has uncovered five major tunnels recently; reports suggest there are dozens.

Finding the entrances to these tunnels – often within houses – and charting their alignment and geology, allows the army to neutralize the threat and, at least, set back the timer on these strategic attacks.

Boots and armor on the ground, moving in tandem, will also allow Israel to reach some of the rockets and launchers that were not targetable from the air and, perhaps more crucially, to gather intelligence. It has been many years since Shin Bet officers were able to question a wide swath of Gazans and an array of Hamas operatives. Each passing day will unearth more information about the whereabouts of terror personnel and weapons.

And yet, since the goal of the operation, at present, is not the re-occupation of the Gaza Strip — but rather a weakening of Hamas, a temporary neutralization of the tunnel threat and a favorable, somewhat more long term agreement at the end of hostilities — there will likely come a time when the army downshifts; searching for tunnel entry holes and rockets and personnel can be Sisyphean. And it is then that the guerrilla soldier, who rarely stands and fights but flees to the interior and circles back, will attempt to strike.

Hamas, though, is not just a classic terror organization. It is, for our purposes, the sovereign in Gaza. It is not only accountable to the people, it is also the controller of territory and institutions. Which is to say, it has what to lose. It has enemies to the left and right – the PA and the Salafist organizations – both of which would like to take control of the Strip.

And it is within those confines, too, that the IDF will be operating.

The trick, after 10 days of aerial bombing and a certain degree of hesitancy to launch a ground operation, is to convince Hamas that Israel, which is militarily strong but currently cautious, is also crazy enough to go all the way.