IS fighters have used looted armored personnel carriers, pick-ups, tankers and dump trucks. They pack them with tons of explosives and weld steel cages around them.
When a position is too well defended for a more conventional advance, a suicide driver steers a truck bomb, protected by the makeshift armor, through enemy fire and straight to his target.
"They are protected from 12.7mm (heavy machinegun) fire and even some RPGs (rocket-propelled grenades). There's so much explosives (inside) that it's still effective at 50 meters (yards)," an Iraq-based military expert said.
Videos of the truck bomb attacks, which IS has also used in the battle of Kobani in northern Syria and on other fronts, show huge explosions that are visible from miles away.
"The damage is bigger than that of a half-ton bomb dropped by a fighter jet," the Western expert said. "Truck bombs are their air force."
Responding to US accusations that his troops dodged battle in Ramadi, Prime Minister Haider al-Abadi defended them by saying the impact of a truck bomb blast was akin to that of "a small nuclear bomb".
IS did not invent what is now known as an SVBIED, or suicide vehicle-borne improvised explosive device.
It is unclear who holds that dubious distinction, and rigged horse carts were used more than two centuries ago, such as in
a failed 1800 assassination attempt against Napoleon in Paris.
The vehicle-borne bomb's formidable potential as a weapon was put on display with the 1920 Wall Street bombing carried out by Italian anarchist Mario Buda, said Mike Davis, author of "Buda's Wagon: A Short History of the Car Bomb".
The Islamic State organization has used suicide car bombs in Baghdad for similar purposes -- to sow terror in the population and paint the authorities as powerless to control and govern.
The group's previous incarnations in Iraq had already detonated 18-wheelers stuffed with explosives during the US military presence, but IS commanders are taking the use of truck bombs to a new level.
"The (IS) offensives in Iraq may be the first time that VBIEDs have been used as part of the order of battle of a large attacking force in Middle Eastern warfare," said Andrew Terrill, professor at the US Army's Strategic Studies Institute.
The Tamil Tigers had integrated suicide car and truck bombs with an infantry assault before IS, but Davis points out they were mostly "solo attacks" to initiate battles.
"The Ramadi attack was shock and awe on a wholly different scale," he said.
A US State Department official said nearly a dozen truck bombs used in Ramadi carried explosives to cause a blast the size of the 1995 Oklahoma City bombing.
Davis said a van bomb such as that used in Oklahoma City were "the explosive equivalent of the bomb load carried by a B-24 in the Second World War. A poor man's air force, so to speak."
"But the truck bombs in Ramadi... were obviously far more powerful and probably the equivalent to an air attack with 1,000-pound bombs," he said.
After the fall of Ramadi, Washington sent 2,000 AT4s to equip Iraqi forces with firepower able to take out the jihadists' lethal truck bombs.
"It's good in the open but it's unguided so if (the truck) is coming at you, you have to stand in front of it," the military expert said of the Swedish-developed anti-tank weapon.
"When the truck is within 100 meters, it's almost too late already," the military expert said. "And in a city, in Ramadi for example, it's almost impossible to avoid the truck bombs."
Thousands of security forces members and allied militiamen are trying to seal Ramadi off as part of an operation to retake it, but Abadi admitted that entering the city was risky.
"We have decided not to fight into the cities... because of those truck bombs, which you cannot see inside the city because there are small roads," he told the BBC this week.
By fully integrating suicide truck bombs carrying huge payloads in ground attacks, IS has already forced a tactical rethink from Baghdad and its allies.
"The greatest military myth of the previous century, of course, was that airpower alone could defeat insurgents," Davis said, adding that truck bombs had helped make IS a "new paradigm".