Question 1: Wasn't this a hugely inefficient and overelaborate way to kill a bunch of civilians? (I.e., here I deal with the moral weight of killing a city worth of people, twice, by retreating into accounting and cynicism.)

> The Manhattan Project [...] employed nearly 130,000 people at its peak and cost nearly US$2 billion (equivalent to about $24 billion in 2021).[1] Over 90 percent of the cost was for building factories and to produce fissile material[.]

> The aerial bombings together killed between 129,000 and 226,000 people, most of whom were civilians.

I assume this is talking about immediate deaths, not eventual deaths due to leukemia, but it's the immediate deaths that are relevant to the war effort, so I'll use those numbers.

"Best case" scenario, then, is that 130k people were employed to kill 226k. That's 1.74 kills per employee.

Similarly, the inflation-adjusted cost of $24 billion works out to $9.4 million per kill.

For comparison, the firebombing of Tokyo -- "Operation Meetinghouse" -- killed 80k to 130k people in a single night.

I find my line of thought has been anticipated by someone on Quora, here:

https://www.quora.com/Which-was-more-expensive-the-atomic-bo...

He says that 1665 tons of incendiary bombs were dropped, and doesn't come up with an exact number, but estimates that the cost must have been lower than the Manhattan Project.

However, to my surprise, the development of the B-29 Superfortress -- the "strategic bomber" (read: indiscriminate city-annihilator) used for both the atomic bombings and Operation Meetinghouse -- cost something like $50B (inflation adjusted).

Thus, it does seem that it would have been more efficient to just scale up firebombing, and this would have resulted in less long term pollution.

But the primary thing is that the cost of B-29 development would have had to have been amortized over a lot more dead civilians for the dollar-per-head number to have gotten down.

But then, war is largely about demonstrating capabilities. You don't need to actually kill fifty billion people, to get your unit economics right; you just have to demonstrate that you could, and then that'll get priced into a surrender and favorable "world order".

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Question 2: Wouldn't the US have contaminated its own land a lot less, and killed a lot fewer of its civilians with cancer, if it had just scaled up firebombing?

The answer seems to be an obvious "yes". The complication is that the Soviet Union might have independently obtained nukes. But it's not clear that other countries would have made such huge investments if the US hadn't demonstrated technological feasibility. It's unclear what a Cold War with conventional weapons would have looked like. Might have been "hotter".

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World War II is difficult to imagine now. Industrial war at that scale. Whole cities annihilated. It's hard to imagine a nation-state even hanging together to conduct such an atrocity. Maybe the case of Russia in Ukraine demonstrates it's still somewhat possible, but even there the scale is lower. Iraq and Afghanistan also, though those quickly turned into messy insurgencies. I would expect more "civil wars" instead. Could absolutely see local Pol Pots whipping mobs up. Or elites doing Potato Famines. But hard to imagine large scale mechanized war, sustained for any long period of time.

The next "strategic" weapons systems might be biological -- viruses. Maintain superior pathogen and vaccine development capabilities. Then just unleash plagues, vaccinating your own people, and withholding the vaccine to others. This has the double benefit that it's also leverage over your own people; you don't need to cajole them into forming organized industrial workforces.