At the military base

According to initial investigations, 40–50 militants infiltrated through the fence system and ran towards the military base near Nahal Oz.^[10] The militants engaged in a brief battle with the guards at the gate, killed them and went inside, and soon destroyed a large part of the post and equipment within it. The soldiers at the post were surprised, and most of them were killed. In the war room, staff officers and observers entrenched themselves and tried to communicate with the forces and direct combat helicopters to the militant squads. A battalion commander and two platoon commanders exchanged fire with the militants outside the war room. This effort continued until the militants threw explosives inside and many were killed.^[6][11]

At the time of the attack, 27 soldiers of Unit 414 of the Combat Intelligence Collection Corps were on duty at this base and were killed or captured by Hamas. Most Unit 414 soldiers at Nahal Oz were female.^[1] Their duty was to conduct reconnaissance on the border with Gaza as well as to operate the remote-controlled gun turrets stationed on the Iron Wall. Most soldiers at Nahal Oz were not provided a handgun or rifle to defend themselves, despite their military outpost being less than a kilometer from Gaza. When Hamas attacked, the base only had a few combat soldiers stationed there. These soldiers were easily defeated. The unarmed Unit 414 soldiers hid in a bomb shelter and almost all of them were killed or captured. According to the Israel Defense Forces twenty Unit 414 soldiers were killed in action at the Nahal Oz base and six were reported missing.^[12][13][14]

The attackers used a flammable substance, which also released toxic gases that caused suffocation within minutes.^[15] As of 13 December 2023, the IDF investigation could not yet pinpoint the exact type of chemicals used.^[15] Of the 22 troups taking shelter in the building housing the surveillance soldiers' command center, only seven managed to exit through a small bathroom window and survive the fumes.^[15]

The 13th Battalion of the elite Golani Brigade suffered 41 killed, which was more fatalities than it suffered in the Six-Day War and Yom Kippur War combined. The battalion headquarters were at the military base at Nahal Oz, but many Golani soldiers were spread out across the Iron Wall and were not defending the base initially. The surveillance buildings at Nahal Oz and their computer equipment were destroyed within the first hour of the invasion.^[16]

Inside the kibbutz

In parallel to the events at the Nahal Oz post, at least 20 and as many as 100 of the militants who carried out the surprise attack infiltrated Kibbutz Nahal Oz near northern Gaza Strip.^[17][6] The militants broke into homes, kidnapped some kibbutz residents, and killed others. The kibbutz's security team responded and battled the militants for hours. The kibbutz security coordinator, Ilan Fiorentino, was killed in the fighting. In addition, a unit of Israel Border Police officers who had been posted to the area a week before arrived in the kibbutz and took part in the fighting. One of the Border Police officers on the scene, Yaakov Krasniansky, was killed while battling numerous militants; his body was found together with the bodies of five militants. Several other Border Police officers were wounded.^[18]

At around 11:30am, approximately 100 Israeli soldiers from the Givati Brigade, originally destined for Sderot, diverted to Nahal Oz and arrived at the kibbutz.^[17] The fighting continued until IDF reinforcements arrived and cleared the kibbutz and nearby army outpost of militants. In the kibbutz, troops went door to door, killing militants. As the kibbutz was cleared, civilians emerged from the safe rooms in their homes where they had been hiding. After regaining control of the kibbutz, the IDF continued to engage isolated attempts by militants to enter the kibbutz via motorcycles and vehicles. The extensive resistance likely prevented the massacre from reaching the scale of massacres that occurred in Nir Oz and Kfar Aza.^[18][17]

Among the victims were Israel Hayom photographer Yaniv Zohar and most of his family,^[5][3] Additionally Eden Nimri, an Israeli international-level swimmer.^[19] As of 17 October, total losses were unknown, at least 12 residents were reported killed, and 20 missing, in addition to the guards and militants who died.^[20]