WASHINGTON — Late in the spring, Iraqi forces fighting the Islamic State in Mosul discovered three unfired rocket-propelled grenades with an unusual feature — a heavy liquid sloshing inside their warheads.
Tests later found that the warheads contained a crude blister agent resembling sulfur mustard, a banned chemical weapon intended to burn a victim’s skin and respiratory tract.
The improvised chemical rockets were the latest in a procession of weapons developed by the Islamic State during a jihadi arms-manufacturing spree without recent analogue.
Irregular fighting forces, with limited access to global arms markets, routinely manufacture their own weapons. But the Islamic State took the practice to new levels, with outputs “unlike anything we’ve ever seen” from a nonstate force, said Solomon H. Black, a State Department official who tracks and analyzes weapons.
Humanitarian de-miners, former military explosive ordnance disposal technicians and arms analysts working in areas captured from the Islamic State provided The New York Times with dozens of reports and scores of photographs and drawings detailing weapons the militant organization has developed since 2014, when it established a self-declared caliphate in Syria and Iraq.
The records show the work of a jihadi hive mind — a system of armaments production that combined research and development, mass production, and organized distribution to amplify the militant organization’s endurance and power.
The resulting weapons, used against the Islamic State’s armed foes on many fronts and against civilians who did not support its rule, were variously novel and familiar. At times they were exceptionally cruel.
One report noted that before being expelled from Ramadi, Islamic State fighters buried a massive explosive charge under a group of homes and wired it to the electrical system in one of the buildings.
The houses were thought to be safe. But when a family returned and connected a generator, their home was blown apart in an enormous blast, according to Snoor Tofiq, national operations manager for Norwegian People’s Aid, which is clearing improvised weapons from areas that the Islamic State left. The entire family, he said, was killed.
Craig McInally, also an operations manager for the Norwegian de-mining organization, described indiscriminate inventions elsewhere — including four seemingly abandoned space heaters and a generator recovered near Mosul.
The heaters and generator, useful to displaced civilians and combatants alike, were packed with hidden explosives. The bombs had been configured, McInally said, so that if a person approached them or tried to move them, they would explode.
Taken together, the scope and scale of Islamic State production demonstrated the perils of a determined militant organization allowed to pursue its ambitions in a large, ungoverned space.
Some weapon components, for example, were essentially standardized, including locally manufactured injection-molded munition fuzes, shoulder-fired rockets, mortar ammunition, modular bomb parts, and plastic-bodied land mines that underwent generations of upgrades. Many were produced in industrial quantities.
The findings also included apparent prototypes of weapons that either were not selected for mass production or were abandoned in development, including projectiles loaded with caustic soda and shoulder-fired rockets containing blister agent.
While the Islamic State has been routed from almost all its territory in Iraq and Syria, security officials say its advances pose risks elsewhere, as its members move on to other countries, its foreign members return home and veterans of its arms-production network pool and share knowledge and techniques online.
“They’re spreading this knowledge all over the world,” said Ernest Barajas Jr., a former Marine explosive ordnance disposal technician who has worked with ordnance-clearing organizations in areas occupied by the Islamic State. “It’s going to the Philippines, it’s in Africa.” He added, “This stuff’s going to continue to grow.”
In a separate development, the United Nations children’s agency said Sunday that 137 children stranded in a rebel-held suburb near the Syrian capital require immediate evacuation amid a crippling siege in which five have reportedly died from a lack of medical care.
The Eastern Ghouta suburb, home to 400,000 residents, has been besieged since 2013 and humanitarian conditions there have deteriorated sharply amid violence that intensified since Nov. 14. The Syrian Observatory for Human Rights says at least 202 people, including 47 children, have been killed since.