In the face of mounting evidence that Hamas was still constructing tunnels despite increased Israeli efforts to prevent that the Israeli government announced in July 2016 that it was going to accelerate the long planned but constantly delayed plan to build a high tech detection and barrier system to prevent Hamas from building tunnels into Israel. Since 2015 this system, called “Obstacle”, has been in the works. But actual construction was repeatedly delayed after it was discovered that Obstacle would cost about $700 million. The Defense Ministry kept telling those living or working near the Gaza border that the project was delayed because of more urgent defense needs. OK, that has been a common problem throughout Israeli history. Then in early 2016 local civilians began reporting (and recording) the sound of tunneling under building near the Gaza border and demanded action. This tunneling activity was confirmed by Israeli intelligence, which used an informant network in Gaza to confirm what a growing number of Palestinians getting out of Gaza, and had worked on the tunnels to confirm the source of the border noise. Some of the Gaza refugees were willing to provide detailed information on how Hamas was going about it. Israel confirmed this new information and found that the only workable defense against these tunnels into Israel (for kidnapping Israelis and carrying out terror attacks) was to scrounge up the cash and proceed with Obstacle. This includes an upgraded security fence along the Gaza border that would employ new sensors and a computer network that would not only assemble sensor data but also rapidly indicate where more scrutiny, or counter-tunnel efforts were required.
All this tunnel anxiety began in 2014 as an after-effect of the mid-year “50-Day War” between Hamas and Israel. The discovery of how much Israel had underestimated the Hamas tunnel system led the Israeli government to promise something that eventually evolved into Obstacle. This was mainly to detect new cross border tunnels Hamas was certain to build after war. Israel has known of Hamas use of tunnels since 2004. Until 2009 most of the tunnels were for smuggling people and goods from Egypt to Gaza. But in 2014 Israel became aware that Hamas was building many more tunnels into Israel as part of a major terror and kidnapping operation. During the 50 Day War Israel found and destroyed dozens of tunnels before leaving Gaza. In order to calm down the thousands of Israelis living near the Gaza border Israel promised to make additions to the Gaza security fence to prevent (or greatly reduce the possibility of) any future Hamas tunnels into Israel.
Another response to tunnel anxiety is the new “tunnel warfare” course the army is giving to troops. This is justified by the extent to which anti-Israel Islamic terror groups have adopted the use of tunnels to get into Israel and shelter their forces when attacked by Israel. Thus the Israeli Army is now giving all their combat troops training in detecting, destroying and fighting in tunnels. To facilitate the training of over 100,000 active duty and reserve troops the army is spending several million dollars to build ten tunnel training facilities. In addition to realistic sections of tunnel, where troops can also use their weapons, there is also a highly detailed computer simulator for planning and carrying out a combat operation against an enemy tunnel.
The main problem Obstacle has to deal with is that over the years Hamas has learned how to dig tunnels that were virtually undetectable. This meant going deep enough to avoid detection by ground penetrating radar or acoustic sensors. This makes it more expensive and time consuming to build tunnels but Hamas diverted much foreign aid (cash and building materials) to the tunnel effort and continues to do so.
Before the ground invasion Israel had been searching for the Hamas tunnels but had only found four of them after two years of searching. In early 2014 Israeli troops found one that was 1,800 meters long and extended 300 meters into Israel. Hamas dismissed this find as a tunnel that had been abandoned because of a partial collapse. But the Israelis said the tunnel had been worked on recently and equipment, like generators, was found in it. The tunnel was lined with reinforcing concrete and was 9-20 meters (30-63 feet) underground. Three of these tunnels were near the town of Khan Younis and apparently part of a plan to kidnap Israelis for use in trades (for prisoner or whatever) with Israel. Israeli intelligence knew Hamas leaders were discussing a much larger tunnel program, involving dozens of tunnels. Most tunnels had no exits in Israel and those were created just before the terrorists were to use them for a nighttime raid into Israel to kill and kidnap. Available tunnel monitoring equipment was slow and often ineffective if there was no one actively working on the tunnel below or if there was no exit (yet) on the Israeli side. Hamas had been building and “stockpiling” these tunnels for at least two years and most of the completed ones could only be detected inside Gaza, where their entrances were. These were also hidden, at least from aerial observation. Israeli intelligence had discovered some of these entrances by detecting the Hamas activity around the entrances (entering and leaving, removing dirt). Hamas tried to hide this activity and Israel knew this meant they probably succeeded in some cases. Thus before the Israeli troops went into Gaza in 2014 commanders had lots of information of where to look. Israeli combat engineers had been trained to destroy the tunnels, which was not easy because Hamas had booby-trapped some of them.
Since the war ended in August 2014 Hamas has gone back to building more tunnels and inspiring other Islamic terror groups to do the same. Hezbollah in Lebanon took the hint is now digging them under the Lebanese border into Israel. So Israel is taking the threat seriously and training most combat troops to deal with it is part of the response.