On 6 August 1945, Colonel Paul Tibbets dropped the first atomic bomb from the B29 Superfortress Enola Gay on the Japanese city of Hiroshima. This weapon, an enriched uranium gun-type design designated “Little Boy,” exploded 1,500 feet above the ground and had a nominal yield of around 15 kilotons. That is an explosive equivalency to 15,000 tons of TNT (trinitrotoluene) high explosive. That blast ultimately claimed between 90,000 and 166,000 lives.
Three days later, the Superfortress Bocks Car was used to deliver a plutonium implosion-type device titled, “Fat Man.” This weapon detonated at an altitude of 1,650 feet and produced a nominal yield of around 20 kilotons. It killed between 60,000 and 80,000 people.
Mind the Weather
The second bombing was an iffy thing indeed. Nagasaki was actually the secondary target. The primary drop point was Kokura, but it was obscured by smoke and clouds. The aircraft commander, 26-year-old Major Charles Sweeney, had to make the call inflight to shift to the secondary.
That decision claimed the lives of tens of thousands of people. The death toll was lower in Nagasaki because of the general topography of the terrain, despite the second bomb’s being 40% more powerful than the first. Regardless, that’s asking quite a lot of a 26-year-old.
And there things remained, for going on 79 years now. Two bombs. Two data points a mere three days apart. These were the only two nuclear weapons ever deployed in anger.
Science Marches On
As of January 2024, the United States maintained 5,044 operational nuclear warheads. The Russians have 5,580. Putin threatens to nuke Ukraine, Germany, Poland, the UK, the US, and most everyone else on the planet about every twenty minutes. There is a fair possibility he might someday actually do that, but nobody takes him seriously right now.
Now ponder the nature of technology since the end of World War 2. This has been the most extraordinary window for scientific advancement in human history. Since that time we have developed microprocessors, space travel, supersonic flight, cellular communications, and precision satellite-based targeting and navigation. The military tools we use today would have been unrecognizable when those two bombs were dropped.
Comparable advances have been ongoing with nuclear bombs as well. While atomic weapons have evolved wildly since then, this evolution has been transparent to most of us. The last American nuclear test took place in September of 1992. Nowadays, we do our nuclear testing digitally. As the last actual deployment of a nuclear bomb occurred at the very dawn of the atomic age in 1945, it is easy to lose track of just how far the state of the art has progressed since then.
Size Matters For Micro-Nukes
Nuclear weapons come in two broad flavors. Fission devices split big atoms into small ones. They typically start with either uranium or plutonium. Little Boy and Fat Man are the archetypal examples.
Fusion weapons operate on an entirely different scale. These devices combine hydrogen to form helium. They use a conventional fission detonation to create the astronomical levels of heat required to support the subsequent fusion reaction. This is the same process that powers the sun. The Hiroshima bomb had a nominal yield of 15 kilotons. The largest fusion bomb ever detonated, the Russian weapon Tsar Bomba touched off in 1961, produced 50 megatons of explosive energy. That’s 50 million tons of TNT or the raw equivalent of roughly three thousand Hiroshima bombs.
Bigger is Better…Or Is It?
Interestingly, Tsar Bomba could have been far more powerful. We have that technology. It was simply that 50 megatons kind of made the point without splitting the freaking planet in half. A typical deployed nuclear weapon like the new American W93 that will sit atop our submarine-launched ballistic missiles will have a yield of around 200 kilotons.
Those numbers boggle the mind. We have no ready frame of reference. The only two bombs that intentionally destroyed anything were both essentially prototypes. Neither performed to its full potential.
Baby Nukes
While it is certainly thought-provoking to imagine how much bigger atomic bombs have gotten in the past several decades, American nuclear scientists explored the other direction as well. One of the smallest deployed nuclear warheads was the M54 tactical weapon that rode aboard the M388 projectile. The M54 was powered by plutonium-239.
Developed in the late 1950s, the M54 was only 11 inches across and 16 inches long. It weighed a mere 50 pounds. You could carry it around in a rucksack or parachute out of an airplane with it. Despite its small size, the M54 still had a nominal yield of up to 1 kiloton. The US Army planned to shoot it off of the back of a jeep.
The Davy Crockett
Uncle Sam christened this man-portable monster the M28 Davy Crockett. A slightly-improved version was designated the M29. This recoilless nuclear gun was adorable, in a dark, sinister, apocalyptic, world-ending sort of way.
An acronym-obsessed US Army called the thing the BGADS or Battle Group Atomic Delivery System. The plan was to shrink these bombs down so small that they could be fired out of conventional artillery pieces or humped into action on the back of some particularly ballsy special operator. The M28 rode about in the back of a standard jeep and had a maximum effective range of 1.25 miles. The subsequent M29 would shoot about twice that far. We built 2,100 of the systems. These weapons were deployed from 1961 through 1971.
Details
The M28 launcher weighed 108.5 pounds unloaded. The M29 tipped the scales at 316 pounds. The intent was to put the power of nuclear weapons into the hands of local Army commanders down to the battalion level. The details are fascinating.
The Projectile, Atomic, Supercaliber XM388 was a little rocket-looking thing, some 279mm in diameter. When equipped with an operational W54 warhead, each round weighed 76 pounds. Expected yield was around 20 tons of TNT. To get there, the XM388 carried 26 pounds of conventional high explosive to be used as a trigger.
The warhead was pure simplicity. There was a basic two-position height-of-burst switch that was user-selectable for either 2 or 40 feet off the ground. There was a binary Safe and Arm switch along with a mechanical time delay. This timer could be set between 1 and 50 seconds. If the time delay was set greater than the time of flight, the bomb would impact the ground and fail to detonate.
The round included four stabilizing fins and a piston in the back. It operated like a spigot mortar. Once the propellant discharged, the piston system shoved into the back of the projectile and resulted in a milder acceleration than might have been the case with a traditional gun-type design. This ensured that the sensitive nuclear components were not subjected to any undue stresses. Troops who used these things called them “atomic watermelons.”
The Micro-Nuke Launcher
The M28 and M29 were muzzleloading weapons. The M28 used an 11-pound explosive cartridge for propulsion, while the heavier M29 used either the same 11-pound charge or a 19-pound propellant unit. Selecting between the two helped establish the desired range. In each case, the back end of the weapon was open to release backblast and negate recoil.
These launchers could be fired from a ground-based tripod or a vehicular mount that fit on either a standard M38 or M151 jeep or an M113 armored personnel carrier. The M113 was set up to carry as many as ten rounds of nuclear ammunition. Weight was always critical, so the barrel was made of titanium and the tripod of aluminum. The smaller M28 broke down into three separate man-portable loads.
Spotter Rifle
The M28 came equipped with a cool 20mm spotter rifle. This single-shot weapon was bore-sighted alongside the launcher and fired depleted uranium spotter rounds. These special rounds mimicked the trajectory of the nuclear projectiles and produced a puff of white smoke upon impact. In action, the crew would align the weapon, fire the spotter rifle to verify the lay of the gun, and then let her rip.
The firing system used by these weapons was also intriguing. The guns fired via a 72-foot length of explosive det cord. The plan was to set up the gun and then take cover someplace less than 72 feet away. Once fired, the piston and projectile would leap out of the launcher tube as a single unit. The piston would then fall harmlessly away as the little mini-bomb continued on downrange. The training materials that were used with the system helpfully suggested that the crew not look at the bomb when it went off as blindness would invariably occur.
Practical Tactical
In action, these guns were quite accurate. M390 practice rounds actually carried 16 pounds of Composition B high explosive and could themselves be used as antipersonnel weapons in a pinch. Training shots typically landed within ten feet of the point of aim.
The W54 micro-warhead was particularly filthy. The instant release of neutron radiation would have been immediately lethal out to a radius of 300 feet. Anyone within 650 feet would succumb to radiation poisoning within minutes. At 1,100 feet you’d be dead in a few hours. At 2,000 feet you’d still be screwed, it just might take a while. The weapon would reliably induce blindness out to 3 miles.
Ruminations On the Micro-Nuke
If that all sounds fairly horrible, that’s because it was. These launchers sported a five-man crew and could be operated by a crew of three in an emergency. I wore the uniform myself for eight years. The idea of junior NCOs tearing about the countryside lobbing little baby nukes hither and yon strikes me as viscerally unsettling. Most of those guys with whom I worked were smart, dedicated, capable, and awesome. However, a few of them I wouldn’t trust unsupervised with Silly Putty.
Thankfully, we never actually touched off one of those tiny little W54 nuclear weapons in anger. We shot two of them for real during testing, one a mere 1.7 miles from the launch crew. They both performed beautifully.
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West German defense minister Josef Strauss coveted a bunch of these things for the Bundeswehr in the worst way. He wanted to equip each German brigade with a Davy Crockett of its own. However, the world had recently had some fairly bad experiences with the Germans, so NATO vetoed that idea.
The Russians made similar stuff, and keeping up with those diminutive rascals after the fall of the Iron Curtain kept many a CIA analyst gainfully employed. With the benefit of hindsight, it is kind of amazing nobody has been stupid enough to light something like this off. However, we live in interesting times. With nukes in the hands of the North Koreans, and likely soon, the Iranians, there’s just no telling what the future holds.
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