The Iraqi forces were able to free Fallujah in an amazingly quick time. The earlier Ramadi campaign took a total of four months to fully secure the city. In comparison, the fight for Fallujah lasted just five weeks. This was a huge surprise since the Islamic State had been in the city since January 2014, which gave it ample time to build up its usual defense in depth like it had in Tikrit and Ramadi. Instead it appeared something completely different happened. The militants built up strong outer defenses, but little inside Fallujah itself, and many fled rather than fight to the death as they had previously.
When the Iraqi forces began their assault upon Fallujah in May 2016 it looked like it would be another long haul such as previous battles. For example, a Niqash article noted that the Islamic State had set up its usual defenses of trenches for fighting positions, tunnels to move secretly and under cover, and had snipers that were taking out vehicles by firing into their engine blocs. There were also reportedly a large number of foreign fighters. Military sources told Niqash that they thought the campaign would be a hard one.
As it turned out IS only put up stiff resistance on the perimeter, but once that was penetrated Fallujah quickly fell. It took four weeks from May 23 to June 16 for the government’s forces to break through the insurgent’s networks and reach downtown. After that the campaign was mostly over with only the northern district of Jolan proving difficult. By June 26, the whole city was declared freed.
IS’s sudden collapse came about due to several factors. First, a member of the Golden Division told the Wall Street Journal, that Fallujah was a command and control center for the militants where it housed its leadership and their families. When the battle started those people were still there, which meant that while there were plenty of IED fields on the outside, there were very few inside. As one Golden Division soldier stated there were fewer booby-trapped houses in Fallujah than in Ramadi. Despite the initial reports, it turned out that there were actually fewer foreign fighters in the city. That meant there were fewer suicide bombers, which was another staple of IS defenses. Third, IS commanders ended up fleeing and telling the rank and file to stay and fight. That caused disarray. Once the leadership exited so did many of the regular fighters. One Iraqi officer said that almost 500 IS elements were able to escape. Those factors along with the growing experience and battle hardened Iraqi troops backed by U.S. air strikes all combined for the quick victory.
Arango, Tim, “A Tour of Falluja Reveals Grim Remnants of Life Under ISIS,” New York Times, 6/22/16
BBC, "Falluja: Iraq PM Haider al-Abadi hails recapture from IS," 6/26/16,
George, Susannah, “IS fled last stand in Fallujah but fears of comeback linger,” Associated Press, 7/1/16
El-Ghobashy, Tamer, “Fallujah’s Importance to Islamic State Helped Iraqi Forces Retake It,” Wall Street Journal, 6/29/16
El-Ghobashy, Tamer, “Iraqis Celebrate Victory in Fallujah One Sniper Too Soon,” Wall Street Journal, 6/18/16
Habib, Mustafa, “Suicide Bombers + Secret Tunnels: Extremists’ Tactics On Fallujah’s Frontlines,” Niqash, 6/7/16