ONLY when he felt a strong arm grabbing him by the neck did Roi, an Israeli infantry soldier, notice the entrance to the hidden tunnel.

His patrol had been sent to search the house of a Hamas militant on the eastern outskirts of Gaza City last week, but found it apparently empty.

As they were clearing it room by room, Roi (not his real name) was separated from his comrades and the militant pounced. Roi called for help, but in vain.

It was a short but brutal hand-to-hand struggle as the Hamas militant tried to pull him into the tunnel. When the Hamas fighter realised he had lost the element of surprise, and that Roi was too big for him to take, he vanished again.

Seconds later Still, a german shepherd dog, moved into action. His handler, a young soldier from the Israeli Oketz (“Sting”) unit, released Still into the tunnel.

There was no sign of him for several minutes, and then to the surprise of his handler, Still’s bark could be heard from the entrance of a large house several hundred yards away.

The soldiers tensed. Still was supposed to bark only when he spotted an enemy.

Then everything happened quickly. The soldiers ran to the house. A short burst of fire from an AK-47 was heard and then a horrible howl from Still.

The soldiers burst in to finish off two Hamas fighters. Still was dead, his blood mixed with that of the militants. Later the soldiers discovered 450lb of booby-trap explosives in the house they thought was empty. Still had saved their lives and his body was sent for burial at the graveyard at the Oketz base.

So busy have Still and his canine colleagues been that exaggerated assessments of their capabilities have spread among Gazans. “Every dog is equipped with a tiny camera attached to one leg and a transmitter on the other leg,” said a Palestinian from the Jabaliya refuge camp.

In truth, the dogs, and the near-kidnapping of Roi, represent the failure of the Israeli military operation in Gaza. After 14 days, the biggest military machine in the Middle East has achieved little. Despite more than 1,000 Israeli air sorties, this weekend Hamas continued to launch rockets and even increased their number.

About 800 Palestinians have been killed, many of them civilians, and more than 3,000 injured, but the main fighting force of Hamas was unhurt and lay in wait for the Israelis in Gaza City and the refugee camps in the north and south of the Gaza Strip.

The Israelis have found an enemy well dug in. In recent years, especially in the last six months of the unofficial ceasefire, Hamas has constructed hundreds of miles of tunnels in urban areas.

“Almost every mosque has a secret entrance that leads to a tunnel that stretches hundreds of metres, sometimes whole kilometres away,” said an Israeli officer.

This network has allowed Hamas fighters to remain almost completely out of sight of the Israelis, and led to house-to-house searches that are harrowing for the local population and nerve-racking for the invaders.

The first accounts from Israeli infantry soldiers about the difficulties of fighting in such conditions have begun to filter back from the front line.

“We ‘jump’ from house to house till we reach the designated house,” said one soldier, who sent his diary home last week. “I was wondering how I would react if a group of soldiers stormed into my house with camouflage colours on their faces at three o’clock in the morning.

“Someone in old pyjamas and frightened eyes opens his front door. I order him to put his hands up and check under his pyjamas to make sure he’s ‘clean’. I tell him to put all his family in one room. If we find an unaccounted person we’ll shoot him, I warn the owner.”

Minutes later the incoming Hamas fire began. “I hear the whistle of the RPG [rocket-propelled grenade]. I trace the launcher and ask my officer for permission to open fire,” wrote the soldier. “The officer asks if I’m certain. I answer positively. Here it comes, I say to myself, the most important thing is to keep my hands steady. A hundred yards in front of me I see a militant with the RPG. I’m onto him. Ask for fire permission. Got it. I squeeze the trigger. A single shot. He collapsed. My first.”

Other techniques used by the Israelis were more subtle. At the beginning of the military operation, 90,000 recorded messages were sent to land lines in the Gaza Strip. The message asked householders not to shelter Hamas men, as by doing so they risked their own lives. Then text messages were sent to known mobile phones of families of militants warning them to evacuate their houses as an attack was imminent.

Such attempts to distinguish militants from civilians will become more difficult if the Israeli cabinet gives the order directly to confront Hamas in Gaza City.

In the Zeitoun neighbourhood, the Givati brigade commander, Colonel Ilan Malka, was realistic about what could await his soldiers. “Hamas ran away but didn’t disappear,” he said. “They are waiting for us.”

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