BAGHDAD — The Islamic State group's top command is dominated by former officers from Iraqi leader Saddam Hussein's military and intelligence agencies, according to senior Iraqi officers on the front lines of the fight against the group, as well as top intelligence officials, including the chief of a key counterterrorism intelligence unit. The experience they bring is a major reason for the group's victories in overrunning large parts of Iraq and Syria. The officers gave ISIS the organization and discipline it needed to weld together jihadi fighters drawn from across the globe, integrating terror tactics like suicide bombings with military operations.Patrick Skinner, a former CIA case officer who has served in Iraq, said Hussein-era military and intelligence officers were a "necessary ingredient" in ISIS's stunning battlefield successes last year, accounting for its transformation from a "terrorist organization to a proto-state." "Their military successes last year were not terrorist, they were military successes," said Skinner, now director of special projects for the Soufan Group, a private strategic intelligence services firm. How officers from Hussein's mainly secular regime came to infuse one of the most radical Islamic extremist groups in the world is explained by a confluence of events over the past 20 years — including a Hussein-era program that tolerated Islamic hard-liners in the military in the 1990s, anger among Sunni officers when the United States disbanded Hussein's military in 2003, and the evolution of the Sunni insurgency that ensued. ISIS's second-in-command, behind Iraqi jihadi Abu Bakr al-Baghdadi, is a former Hussein-era army major, Saud Mohsen Hassan, known by the pseudonyms Abu Mutazz and Abu Muslim al-Turkmani, according to the chief of a key Iraqi counterterrorism intelligence unit. Hassan also goes by Fadel al-Hayali, a fake name he used before the fall of Hussein, the intelligence chief told the Associated Press. Like others, he discussed the intelligence on condition of anonymity. During the 2000s, Hassan was imprisoned in the U.S.-run Bucca prison camp, the main detention center for members of the Sunni insurgency, where al-Baghdadi also was held. The prison was a significant incubator for ISIS, bringing militants like al-Baghdadi into contact with former Hussein officers, including members of special forces, the elite Republican Guard and the paramilitary force called Fedayeen. In Bucca's Ward 6, al-Baghdadi gave sermons and Hassan emerged as an effective organizer, leading strikes by the prisoners to gain concessions from their American jailers, the intelligence chief said. Former Bucca prisoners are now throughout the ISIS leadership. Among them is Abu Alaa al-Afari, a veteran Iraqi militant who was once with al-Qaida and now serves as the head of ISIS's "Beit al-Mal," or treasury, according to a chart of what is believed to be the group's hierarchy provided to the AP by the intelligence chief. Al-Baghdadi has drawn these trusted comrades even closer after he was wounded in an airstrike this year, the intelligence chief said. He has appointed a number of them to the group's Military Council, believed to have seven to nine members — at least four of whom are former Hussein officers. He brought other former Bucca inmates into his inner circle and personal security. Hussein-era veterans also serve as "governors" for seven of the 12 "provinces" set up by ISIS in the territory it holds in Iraq, the intelligence chief said. Iraqi officials acknowledge that identifying ISIS leadership is an uncertain task. Besides al-Baghdadi himself, the group almost never makes public even the pseudonyms of those in its hierarchy.Estimates of the number of Hussein-era veterans in ISIS ranks vary from 100 to 160 in mostly mid- and senior-level positions, according to the Iraqi officials. Typically, they hail from Sunni-dominated areas, with intelligence officers mostly from western Anbar province, the majority of army officers from the northern city of Mosul, and members of security services exclusively from Hussein's clan around his hometown of Tikrit, said Big. Gen. Abdul-Wahhab al-Saadi, a veteran of battles against ISIS north and west of Baghdad. For example, a former brigadier general from Hussein-era special forces, Assem Mohammed Nasser, also known as Nagahy Barakat, led a bold assault in 2014 on Haditha in Anbar province, killing around 25 policemen and briefly taking over the local government building. Many of the Hussein-era officers have close tribal links to or are the sons of tribal leaders in their regions, giving ISIS a vital support network as well as helping recruitment. These tribal ties are thought to account, at least in part, for the stunning meltdown of Iraqi security forces when ISIS captured the Anbar capital of Ramadi in May. Several of the officers interviewed by the AP said they believe ISIS commanders persuaded fellow tribesmen in the security forces to abandon their positions without a fight. Skinner, the former CIA officer, noted the sophistication of the Hussein-era intelligence officers he met in Iraq and the intelligence capabilities of ISIS in Ramadi, Mosul and in the group's de facto capital of Raqqa in Syria. "They do classic intelligence infiltration. They have stay-behind cells, they actually literally have sleeper cells," Skinner said."And they do classic assassinations, which depends on intelligence," he said, citing a wave of assassinations in 2013 that targeted Iraqi police, army, hostile tribal leaders and members of a government-backed Sunni militia known as Sahwa.