The Actual Operation begins
The Prophet [pbuh] began the campaign by reducing the minor strongholds one after the other. The first fort he was to attack was Na‘im, the first defence line with a formidable strategic position. Marhab, the leader of the fort, invited ‘Amr bin Al-Akwa‘ to meet him in combat and the latter responded; when ‘Amr struck the Jew, his sword recoiled and wounded his knee, and he died of that wound. The Prophet [pbuh] later said: "For him (‘Amir) there is a double reward in the Hereafter." He indicated this by putting two of his fingers together. ‘Ali bin Abi Talib then undertook to meet Marhab in combat, and managed to kill him. Yasir, Marhab’s brother, then turned up challenging the Muslims to a fight. Az-Zubair was equal to it and killed him on the spot. Real fighting then broke out and lasted for a few days. The Jews showed courage and proved to be too formidable even to the repeated rushes of the veteran soldiers of Islam. However, they later realized the futility of resistance and began to abandon their positions in An-Na‘im and infiltrate into the fortress of As-Sa‘b.
Al-Hubab bin Al-Mundhir Al-Ansari led the attack on As-Sa‘b fortress and laid siege to it for three days after which the Muslims stormed it with a lot of booty, provisions and food to fall to their lot therein. This victory came in the wake of the Prophet’s [pbuh] invocation to Allâh to help Banu Aslam in their relentless and daring attempts to capture that fort.
During the process of the war operations, extreme hunger struck the Muslims. They lit fires, slaughtered domestic asses and began to cook them. When the Prophet [pbuh] inquired about the fires and cooking, he ordered that they throw away the meat and wash the cooking pots, forbidding the practice of eating such meat.
The Jews, meanwhile, evacuated An-Natat and barricaded themselves in Az-Zubair fort, a formidable defensive position inaccessible to both cavalry and infantry. The Muslims besieged it for three days, but in vain. A Jew spy told the Prophet about a subterranean water source that provided them with water, and advised that it be cut off in order to undermine their resistance. The Prophet [pbuh] did that so the Jews got out to engage with the Muslims in fierce fighting during which some Muslims and ten Jews were killed, but the fort was eventually conquered.
Shortly after this battle, the Jews moved to ’Abi Castle and barricaded themselves inside. The same events recurred; the Muslims besieged the new site for three days and then the great Muslim hero Abu Dujanah Sammak bin Kharshah Al-Ansari — of the red ribbon — led the Muslim army and broke into the castle, conducted fierce military operations within and forced the remaining Jews to flee for their lives into another fort, An-Nizar.
An-Nizar was the most powerful fort, and the Jews came to the established conviction that it was too immune to be stormed, so they deemed it a safe place for their children and women. The Muslims, however, were not dismayed but dragged on the siege, but because standing at a commanding top, the fort was impregnable. The Jews inside were too cowardly to meet the Muslims in open fight but rather hurled a shower of arrows and stones on the attackers. Considering this situation, the Prophet [pbuh] ordered that rams be used and these proved effective and caused cracks in the ramparts providing an easy access into the heart of the fort, where the Jews were put to rout and fled in all directions leaving behind their women and children.
With these series of military victories, the first division of Khaibar was totally reduced, and the Jews in the other minor fortresses evacuated them and fled to the second division.