As ISIS mortars began to rain down onto the advancing convoy of Kurdish commandos in October, three trucks raced to slam into their Humvees and waylay their assault on Mosul. A Kurdish gunner took aim at the first bomb-laden truck with an anti-tank missile and fired.

ISIS fighters are relying on suicide attacks to decimate and demoralize the Iraqi and Kurdish forces working to uproot them from northern Iraq’s largest city, a difficult effort where progress is often measured in blocks. As of Tuesday, ISIS has deployed at least 208 suicide bombers — most but not all in vehicles — over a 56 day span. Researchers say it is the largest deployment of suicide attackers in modern history, since the kamikaze attacks used seven decades ago by Imperial Japan.

“They’ve got the numbers of willing bombers and experience to turn these attacks into a sort of close air or artillery support for an army that lacks planes to support their conventional operations,” said one Western security advisor working in the region, who asked for anonymity out of concern for his personal safety. “And it’s bloody effective.”

“Call them a poor man’s JDAM, if you will,” he added, referring to the GPS-guided bombs used by fighter jets.

And although the numbers haven’t reached the industrial scale of that Japanese effort, ISIS has long favored suicide attacks as a force multiplier to support conventional military operations and the group appears to have a deep supply of fighters willing to incinerate themselves by piloting the explosive-laden cars and trucks into enemy front lines.

"It's not easy for us. They are suicidal," Omar Salem, a 23-year-old gunner on the Kurdish convoy, had warned the night before the October attack, when a BuzzFeed News reporter and photographer accompanied the unit as it assaulted ISIS defenses outside northern Mosul. "You can't expect what they're going to do. There is no space for failure."

During that assault on Mosul the next day, the anti-tank missile struck the first suicide truck as it sped across a dusty field, detonating it in a blast whose force shuddered the armored Humvees in the Kurdish convoy. Within minutes a second truck bomb, this time covered in a makeshift armor of thick metal plating impervious to gunfire, was on its way, only to be detonated by another anti-tank missile. Later, the soldiers also destroyed a third bomber.

Guided anti-tank missiles are the most effective means to destroy car bombers, and one the Kurds have lobbied for after ISIS’ 2014 seizure of Mosul.

A few weeks later, on a visit to Iraqi Special Forces aligned with the Kurds – while nominally part of Iraq, the Kurds operate their own government and military forces largely independently of the central government — soldiers described car bombs, or vehicle-borne improvised explosive devices in military jargon, as the single biggest threat and cause of casualties in the Mosul assault.

These terrifyingly effective weapons are an obsession for the troops who call in U.S.-led airstrikes. These forward air controllers are often posted close to battle to rapidly radio in US and coalition airstrikes on suspected bombers.

A top commander with Iraqi Special Forces calls the deployment of scores upon scores of the attackers as a critical part of ISIS’ defensive plan for Mosul that has forced the attacking coalition to move much more slowly as the fighting had shifted to the densely populated urban cityscape where sight lines — and the effectiveness of overhead air support — are much more limited.

"We were like the rat and they were the cat," Maj. Salam Hussein, the commander of the special forces unit leading the charge in Mosul, said one night after being menaced by a car bomb team most of the day.