Title. I was browsing r/shockwaveporn a bit ago and saw that many if the explosives are airbursts. If I’m not mistaken, the nukes dropped on Hiroshima and Nagasaki were airburst too. Why?
In: Physics
It’s not that they are more deadly, per se. It’s that with an airburst at the right height, you not only avoid a lot of “shielding” effects that things on the ground might provide (because you’re applying the pressure and heat from above, not from the side), but you also can make the blast wave reflect off of the ground and interact with itself, increasing its range by a significant amount.
A nuclear weapon airburst at the right height can disperse a medium-amount of blast pressure over about twice the area as one detonate at ground level. However one detonated at ground level will apply much higher blast pressures in the immediate vicinity of the blast. So depending on the kind of target you are attacking, you might choose one or the other. If you want to destroy a target particularly vulnerable to medium and light blast damage — like a city — you use an airburst calibrated to enhance that kind of damage. If you want to destroy a heavily-fortified target — like a silo or bunker — you’ll want it to be a surface burst, so it applies ridiculously high pressures right on the target.
Hiroshima and Nagasaki were airbursts because the goal was to destroy their civilian infrastructure. The planning documents were explicit about this, and they even spent time debating how much blast pressure you’d need to really destroy a Japanese house. An additional benefit was that airbursts do not create a lot of nuclear fallout contamination (which is good when you intend to occupy the city later), but that was not the primary consideration for the height of the bursts.
Separately, for something as complicated and fragile as a nuclear weapon (it is a weapon that requires very high precision in timing and operating of its internal electronics and explosives), it is actually harder to make a fuze that detonates on impact (before the bomb gets damaged by said impact) than it is to make it detonate in the air (which you can do using a number of methods, like bouncing radar signals off of the ground). So the earliest nuclear weapons were _all_ airbursts (though you could change the height to pretty low if desired) because it took some time to develop reliable means of detonating them on impact.
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