They hide under residential neighborhoods, storing their weapons in miles of tunnels and in houses, mosques, sofas — even a child’s bedroom — blurring the boundary between civilians and combatants.

They emerge from hiding in plainclothes, sometimes wearing sandals or tracksuits before firing on Israeli troops, attaching mines to their vehicles, or firing rockets from launchers in civilian areas.

They rig abandoned homes with explosives and tripwires, sometimes luring Israeli soldiers to enter the booby-trapped buildings by scattering signs of a Hamas presence.

Through eight months of fighting in Gaza, Hamas’s military wing — the Qassam Brigades — has fought as a decentralized and largely hidden force, in contrast to its Oct. 7 attack on Israel, which began with a coordinated large-scale maneuver in which thousands of uniformed commandos surged through border towns and killed roughly 1,200 people.

Instead of confronting the Israeli invasion that followed in frontal battles, most Hamas fighters have retreated from their bases and outposts, seeking to blunt Israel’s technological and numerical advantage by launching surprise attacks on small groups of soldiers.

From below ground, Hamas’s ghost army has appeared only fleetingly, emerging suddenly from a warren of tunnels — often armed with rocket-propelled grenades — to pick off soldiers and then returning swiftly to their subterranean fortress. Sometimes, they have hid among the few civilians who decided to remain in their neighborhoods despite Israeli orders to evacuate, or accompanied civilians as they returned to areas that the Israelis had captured and then abandoned.