I guess the immediate response to this question would the U-235. This is the stuff (an isotope of Uranium-238, a fissile element that causes a rapidly expanding fission chain reaction), the heart of the atomic bombs that were exploded over Hiroshima and Nagasaki.
On 6 August, 1945, the nuclear weapon “Little Boy” was dropped on Hiroshima, killing as many as 140,000 people, many of those dying lingering deaths over the course of the next few months; the bomb “Fat Man” was detonated over Nagasaki three days latter, and killed 80,000 over the same period. Most people died of radiation and its extended influences than were killed in the initial moments of the bombs’ explosions.(Below is an image of Nagasaki, before and after.)
[Image source: Roger Williams University Archives]
The components of M-69 were naphthemic acid, palmitic acid, aluminum soap, oleic acid, and gasoline. They were placed in tubes about two inches in diameter and 20 inches long, then placed in a 19-unit hexagonal, bound, and located in a bomb shell with a three-foot long paper tail (to slow its descent)..
When this bomb was exploded about a hundred feet over the ground, it was dispersed like a burning, sticky aerosol, and attached itself to anything that it could find. It burned more furiously than any other incendiary device, exhausting as fuel whatever flammable thing it contacted. It could also be dropped all the way to the ground, where it would lay for some number of seconds before exploding, sending dozens of flaming fragments (embedded in cheesecloth) flying in all direction, for a hundred yards or more, looking for flammable things to eat. One such bomb—a 6-pound unit—could start dozens of fires.
This was a product of the US Army Chemical Warfare Services, and manufactured by Nuodex Products and the Arthur D. Little Company. (The Arthur D. Little Company--today an international management firm--was also instrumental, at the same period of time, in producing the first massively-available dosages of penicillin.) The flammable element is more commonly known now as napalm. In a popular article in Collier's Magazine (14 April, 1945), the M-69 was dubbed “Tokyo Calling Cards”
On March 9-10, 1945, 339 B-29’s dropped 2000 tons (4 million pounds, about 496,000 bombs) of M-69 on Tokyo. Two initial passes were made on the city, marking a large, burning “X” in the city. Each plane had the capacity to cover a drop area of 350 feet by 2000 feet, which means a much greater area was affected. The citizens of Tokyo met their ends with buckets of water and brooms in defense. Hours later fifteen square miles of the city were destroyed. In the months prior to Hiroshima and Nagasaki, 66 cities were bombed with M-69, killing about a million people, and wounding more. (Photo below shows Tokyo, before and after.)
Its easy to remember the destruction of the atomic bombs of August, mainly I think because of what those bombs became. I don’t know why the 1945 series of firebombings of Japan aren't recalled as often, especially given the continuing employment of the heart of the weapon that caused that destruction. Perhaps it is the sheer inconceivable nature of what the atomic bombs became, while napalm, as terrible as it was/is, is knowable, somehow.I’m not at all sure. But I think the M-69 should be brought up for discussion every now and then, and remembered.