During the nine month battle for Mosul in 2016-17 ISIL (Islamic State in Iraq and the Levant) used an unexpectedly large number (over 600) of suicide car bombs (SBVIEDs. Or Suicide Vehicle Borne Improvised Explosive Devices). The large scale car bomb operations actually began at the end of 2015 as Iraqi forces began encircling Mosul and massing forces for the October combined assault on the city. At that point 80-90 percent of ISIL suicide bomb operations were for military, not terror, operations. It soon became apparent that this increased and more elaborate use of suicide car bombs was also using new and rapidly evolving tactics. This was confirmed during the months of fighting around Mosul when electronic surveillance, captured documents and interrogations of captured ISIL men and refugees who had witnessed the massive suicide car bomb effort. ISIL found that the suicide car bomb attacks were potentially very effective in urban areas that provided lots of hiding places for the bomb equipped (with up to a ton of explosives) vehicles could be hidden and streets could be blocked with rubble using roadside bombs or barricades so the advancing troops would use routes near where the suicide car bombs were waiting. At the same time suicide car building workshops were larger and less mobile that similar operations for smaller weapons ammo, meaning they were easier to find.
During the main battle (October 2016-July 2017) the ISIL 11,000 or so defenders were outnumbered 10-1 and 90 percent of the ISIL force died during those nine months as did about 1,400 of the attackers (in addition to over 7,000 wounded). About 6,000 civilians were killed, many of them when used as human shields by ISIL or victims of the many bombs set off by the defenders without regard for nearby civilians. ISIL hoped the mass use of suicide car bombs would make a big difference and perhaps even cause enough casualties among the attackers to stall or stop the offensive. Like the Japanese use of Kamikaze suicide aircraft attacks late in World War II, it was a surprising and spectacular effort, but in both cases these tactics failed.
During the Mosul campaign most of the suicide car bombs were used in the relatively open areas of eastern Mosul, the area on the east bank of Tigris River. This phase of the battle lasted for three months and ISIL averaged about 2o suicide car bomb attacks a week during the first two months. Because of the large number of surveillance and attack aircraft used to support the Mosul operation most of the suicide car bomb operations moved to more open areas around Mosul and continued to be a factor until west Mosul and entire city was declared completely captured in mid-2017.
ISIL, and its Iraqi predecessor (several Islamic terror groups mainly working with the Iraqi branch of al Qaeda) used several thousand car bombs, not all of them driven by a suicide bomber, from 2004 to the present. What characterized the large number encountered in the early stages of the Mosul battle was the fact that about a fifth were fitted with armor and several dozen had a second man operating a machine-gun in an armored turret to help clear the way to a well defended target. Often there were coordinated attacks when up to a dozen suicide car bombs would be deployed according to a battle plan, often with the help of commercial UAVs scouting the route and directing the driver to avoid blocked streets (often by bomb craters put there deliberately by Iraqi forces) and get them to Iraqi forces. By the end of 2016 the suicide car bomb workshops that continued to build these vehicles were searched for and hit with air or artillery attacks.
The large scale use of suicide car bombs was not totally unexpected. Islamic terrorists in general had come to use multiple car bombs for attacks, typically as distractions for the defender and then to breach the main entrance to the target (a well-guarded base or compound) that enabled Islamic terrorists on foot, including many equipped with explosive vests as well as assault rifles, to get into the base/compound/building to do maximum damage. What made Mosul unique was that ISIL built numerous workshops to convert all sorts of vehicles (cars, SUVs, vans, trucks and captured military transports like hummers, already armored hummers and tracked vehicles like APCs or even bulldozers). The strict security in ISIL controlled Mosul was partly to prevent the attackers from knowing much about the suicide car bomb stockpile and the extent of the workshops that were stocked with a lot of additional vehicles and explosives so that production could be quickly increased. The coalition, especially the Americans with their extensive fleet of surveillance aircraft (UAVs and manned aircraft carrying all sorts of sensors), knew something was up and when it became apparent exactly what, all that data was used to attack known and suspected workshops and tweak the search criteria to concentrate on workshops or suicide car bomb storage sites (near where ISIL expected they would be needed). ISIL adapted and when it was all over some surviving workshops were found. But most had been detected and destroyed in the course of the fighting.
During the last six months of the Mosul campaign suicide car bomb use was often successfully anticipated and countered with airstrikes or even ambushes on the ground. ISIL commanders were not surprised how quickly the American intelligence analysts detected changes in tactics and quickly used smart bombs and missiles to destroy the threat. Still, ISIL continued to capture videos of the suicide car bomb attacks, often using their cheap camera equipped quad-copters to get aerial views of the final moments of vehicle movement and then the large explosion. Some vehicles were fitted with additional quantities of fuel oil to create a lot of smoke and cover other ISIL forces advancing on foot or in vehicles. The videos were used to encourage the defenders as well as to show potential recruits around the world that the defense of Mosul was photogenic.
The coalition was less eager to distribute videos of the countermeasures, because that would enable ISIL to better adapt. Once the Mosul battle was over more details (and videos) of coalition tactics did appear. Basically it was a matter of finding and destroying the car bomb before it could be used. In some cases ISIL used elaborate camouflage and other forms of deception to make the vehicle appear harmless. Any technique rarely worked more than once. Many of the Iraqi troops on the ground had years of experience and put frequent (often daily) intelligence updates to use right away. Given that these suicide vehicle bombs and an average of about a ton of explosives on board they created a larger explosion than the biggest smart bomb (the 2,000 pound/909 kg bomb) which contained, at most, half a ton of explosives. From a distance you could nearly always tell the difference between a suicide car bomb and smart bomb going off. The coalition deliberately used lots of smaller missiles and smart bombs to limit the damage and injuries to nearby civilians. ISIL had different priorities.