Atomic Weapon Safety Controls

US atomic weapons have very sophisticated electronic safety controls, I believe. One feature I do know they have is that they cannot be set off without being transported to a certain height and falling. This is to prevent someone from stealing one and transporting it to New York, for instance.

How were these safety features controls incorporated into these weapons in the days before sophisticated miniature computers?

Just curious.

I did find this:.

The most sophisticated of the early safety and control
systems, environmental detection sensors (EDSs) demanded
that the weapon undergo the expected sequence
of physical motions before the warhead is completed
armed. The Genie Air-to-Air Missile, for instance, demanded
periods of acceleration and deceleration while
many gravity bombs could not be armed below a specified
Environmental sensing is highly effective in preventing
accidental detonation, but only if not accompanied by
an accidental launch or release. Similarly, an adversary
who has obtained access to a nuclear weapon with environmental
sensing would be required to launch it in the
expected fashion. While clearly imperfect, environmental
sensing does improve the situation and the technique
is used ubiquitously today. In fact, many weapons use
environmental sensing as both an interlock and a fuse.
For instance, a gravity bomb may arm only if it first
reaches a specified altitude then begins freefall and subsequently
detonate once it reaches a different altitude or
experiences a sudden deceleration

Nuclear bombs have always had safety devices but they haven’t always worked that well. The U.S. Air Force almost detonated one over North Carolina in 1961 when the B-52 that was carrying it broke up in mid-air. Three of the four safety devices meant to prevent an accidental detonation failed. It was only the fourth and weakest one that prevented a major catastrophe. The bomb, about 260 more powerful than the Hiroshima bomb, received the detonation signal to its core but the final safety held thankfully. This incident will tell you about the safety devices in use during that time period.

Try Eric Schlosser’s recent book Command and Conquer.

He goes into a lot of detail on this. Part of the problem is the inherent conflict between the military’s desire to have the weapon quickly available and useable, and safeguarding against various accidents and unauthorized use.

My question is specifically about the environmental sensing quoted above. I am curious about how it was accomplished without sophisticated computers. It says these were ‘early’, and I assume that was in the 50s and 60s.

Oh, if you mean the devices that made them detonate at certain altitudes, the early ones used basic barometric altimeters. Richard Rhodes’ book The Making of the Atomic Bomb describes how the Hiroshima and Nagasaki weapons had multiple altimeters, and some number of them had to agree in order to detonate.

The simple answer is they didn’t. I mean, there were safeties - a barometer, arming wires that had to be pulled out, a radar altimeter that has to see the ground approaching.

But in practice, nothing stopped someone who could get their hands on a device who understood the internals from setting it off.

Command and Control goes into this in great detail. One of the more interesting observations was that many of the public statements made by leaders of strategic air command and others were flat out bluffs and lies. In a situation where a government institution can maintain absolute secrecy…they tend to lie whenever they like.

Command and Control… not Conquer.

I think the term the OP is looking for is permissive action link.
In particular:

The other tension in any safety system is that any time the safety malfunctions by not releasing when it should, you’ve created a dud. So as much as you want the entire bomb to fail by failing safe, you want each of the redundant safety systems to fail by failing hot.

The enemy will not give you a do-over or laugh off a dud arriving at one of their vital facilities.

There was an issue with a safety system on the early model Polaris SLBM which rendered almost the entire inventory duds. Which defect was not discovered until after a few years of patrolling the seas with them, intending the threaten 2nd strike doom upon the USSR.
As to the OP’s specific question, the answer is simply that these devices were much simpler than what you’re imagining.

As a 100% made-up example: It’s easy to build a barometer-like device which closes a microswitch at a given pressure. And to connect that to a latching relay so once the switch closes a circuit stays in that new state forever. Install two such barometers set for, say, the pressure at 25,000’ and 15,000’ ft. Then build a simple circuit out of some relays & a timer that requires the following events in sequence:

  1. An arming switch closes when the bomb leaves the airplane (or more precisely, when a wire is pulled out of a connector on the exterior of the bomb).

  2. The 25,000’ barometer fires. which starts a timer which runs for a few seconds.

  3. The 15,000’ barometer fires BEFORE the timer runs out. The time interval is chosen to be just a little longer than the time of freefall from 25,000’ to 15,000’.

Bottom line: For a half-dozen relays, 2 barometers, and a timer, you’ve got a mechanism which ensures the bomb got dropped from above 25,000 ft.

Remember these bombs were big, like the size of small passenger cars. And incredibly expensive. So that means there was plenty of physical space for however much 1950’s electronics they needed and batteries to power them. And cost of the fuzing & safety mechanisms is/was immaterial to the total cost of the weapon.

To my mind the truly hard part of these kinds of designs is building them to be tamper-proof or at least highly tamper-resistant. If the bad guys stole a bomb, they could tinker with the safing mechanisms at their leisure until they figured out how they work and how to bypass, remove, or fool them.

Kinda like protecting your laptop data from assault over the internet is very different from protecting it from a techie bad guy who’s stolen it and has your hard drive laying naked on his workbench.

While the technology has certainly changed over the decades, arming and firing LRUs (along with bomb fuzes) have always been very sophisticated. I know this firsthand.

Apparently you want more detail. If I am working on these systems in our lab, and someone inquires on how they work, I respond with, “Do you have a need to know?” :slight_smile: