(NewsNation) — As Israeli Defense Forces engage with Hamas in Gaza, the militant group’s extensive network of tunnels may play a significant role in the fighting.

For years, Hamas has used these spaces under the Gaza Strip to move people and materials.

In recent years, those tunnels were also used to launch attacks within Israel; however, the Israeli military had destroyed many of the ones leading into the country.

Still, the network of tunnels under Gaza, sometimes referred to as the “Gaza Metro,” may have played a role in hiding hostages who were taken from Israel into the territory.

The Israeli military expects these underground spaces to include everything from electrical generators to intelligence rooms.

Hamas militants could use these spaces to move combatants around and transfer weapons, complicating the response from the Israeli military.