The CBU-55 was a cluster bomb Fuel Air Explosive that was developed during the Vietnam War, by the United States Army, and was used only once in warfare. Unlike most incendiaries, which contained napalm or phosphorus, the 750 pound CBU-55 was fueled primarily by propane. Described as a "the most powerful non-nuclear weapon in the U.S. arsenal," the device was one of the more powerful conventional weapons designed for warfare.