Israeli Master Sgt. Omri Erental was kneeling at the mouth of a tunnel shaft in Gaza, standing guard while waiting for a specialized unit to arrive, when he suddenly spotted movement down below.

Other soldiers in his Israel Defense Forces combat engineering unit had already thrown two grenades into the tunnel shaft, so Erental turned his flashlight on.

He then felt a hammer-like impact, as if “hot lava just punched into my face,” he recalled.

The impact was a 7.62-millimeter bullet that pierced his cheek and took out a fragment of his jaw, before lodging in his neck — very close to critical nerves and arteries, according to Erental and his doctor. As Erental crawled back to safety, his fellow soldiers killed the militant who shot him from inside the tunnel, he said. 

Exposing tunnels is central to the Israeli military’s campaign against Hamas in the Palestinian enclave, but the work presents big challenges and dangers. Israel uses enormous bunker-busting bombs to penetrate deep underground, targeting what it says are Hamas command centers and fighters — but these often leave gaping craters where civilian buildings once stood and can kill large numbers of civilians.

Members of Israel’s combat engineering forces also send drones, dogs and sometimes troops deep into booby-trapped tunnels in order to clear them of Hamas fighters, uncover potentially useful intelligence, and then ultimately detonate them.

Israeli officials believe that many Hamas fighters — including Gaza leader Yahya Sinwar — are surviving in sophisticated tunnels equipped with electricity, bathrooms and stocks of food and water.

Watch Jeremy Diamond's report: