JERUSALEM — Israel entered its latest conflict with Hamas armed with a high-tech arsenal, real-time battlefield intelligence and strong domestic support for dealing a heavy blow to Hamas.

But again on Friday, Israeli forces were taken by surprise, this time with two soldiers killed and one taken prisoner when militants once again attacked from a tunnel in Gaza.

As frustration grows in Israel over the military’s limited success so far in trying to neutralize Hamas, the militant Islamic group that governs Gaza, some military experts say it is increasingly evident that the Israel Defense Forces have been operating from an old playbook and are not fully prepared for a more sophisticated, battle-ready adversary. The issue is not specifically the tunnels — which Israel knew about — but the way Hamas fighters trained to use them to create what experts in Israel are calling a “360-degree front.”

“Hamas has changed its doctrine and is using the tunnels as a main method of operation,” said Israel Ziv, a retired general who headed the military’s Gaza division and its operations directorate. “This is something we learned amid the fighting.”