Nuclear Bomb Effects Computer Source Code Repository Now on GitHub

Since 2005, Fourmilab’s “Strangelove Slide Rule: Nuclear Bomb Effects Computer” has provided a Web-based implementation of the weapons effects calculator originally provided as a circular slide rule accompanying the U.S. government book The Effects of Nuclear Weapons. This book was last published in 1977, and since the 1990s used copies have become difficult to obtain and expensive. The companion calculator, originally sold for US$ 1, became almost impossible to obtain.

Rather than re-implement the calculator as a conventional computer query mechanism, I decided to emulate the actual slide rule. This preserves the intuitive grasp of the relationships between inputs and output that the original calculator provides and allows the user, once having set up the parameters, to read off all possible solutions at once. Here are the user instructions that explain how to use the calculator and interpret the results.

In addition to the on-line edition of the bomb effects computer, for those who prefer a tangible tool, and/or one which can be used in a post-apocalyptic environment when there may not be an Internet or electric power, downloadable files and instructions are provided to build your own nuclear bomb effects computer.

All of the source code for these resources are now maintained in and available from the GitHub repository, “Fourmilab/bombcalc_nuclear_bomb_effects_computer”. Everything posted on the Web, and everything needed to replicate the interactive service, is included in the repository. The interactive calculator is a collection of programs which use the Common Gateway Interface (CGI) mechanism, using both standard Linux system and custom programs to respond to queries. Setting up a such a server requires a modicum of specialised knowledge and the ability to customise the installation for the environment of a specific server. This isn’t a drop-in process, but everything you need is in the repository. In addition, the repository maintains a log of all changes made to the calculator Web pages and service, and allows those who choose to mirror it to keep up to date.


Very good forsight, in planning for lack of electricity, in post WW3 world. However, considering the pending high price of paper, I suggest a clay tablet version of the classic Nuclear Bomb Effects Computer (Version 3.0, likely “final” version.)

Below is a prototype of base, and perhaps mica can be used for layer 1, 2, etc.



Surely all we need is our normal watch? After the nuclear explosion, look at your watch. If you can still see it, you survived! :grinning:

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That is an absolutely fascinating slide rule – and a really neat software implementation. The ability to rotate the sector to the top is quite original, and very useful. Great job, Mr. W!

The rapid decline of destructive power with distance does make the case that precise guidance is more important than raw explosive power. If I understood the scales (Big If!), a 1 Kiloton explosion 1 mile away would give a maximum overpressure of about 1.5 psi – minor probably non-fatal damage. To get the same effect one order of magnitude further away (10 miles) would require a 1,000 Kiloton explosion (three orders of magnitude).

Of course, there is room for debate on whether it would be worth surviving the initial explosion.

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This is why the total yield of world nuclear arsenals has been declining rapidly as precision guidance has improved, and conventional weapons can now accomplish many objectives assigned to nukes in the 1950s and 1960s.

There is one non-obvious effect in the tradeoff between yield and distance which can be explored with the calculator. The effects of prompt radiation are significant only for detonations with small yield at close range. For a larger yield weapon, the radius at which prompt radiation effects are lethal or disabling is less than that where thermal and blast effects are 100% lethal, so apart from fallout, radiation can be neglected in the case of large detonations.

This is why small battlefield tactical nuclear weapons such as Davy Crockett were of dubious utility. It needed to be fired at near its maximum range (with attendant poor accuracy) to avoid killing the launching crew with prompt radiation.