Today in History - Davy Crockett Test

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Lorenzo von Matterhorn
Jan 31, 2009
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Anyone flown a scale model of this?

Davy Crockett: King of the Atomic Frontier

On 17 July 1962, a caravan of scientists, military men, and dignitaries crossed the remote desert of southern Nevada to witness an historic event. Among the crowd were VIPs such as Attorney General Robert F. Kennedy and presidential adviser General Maxwell D. Taylor who had come to observe the “Little Feller I” test shot, the final phase of Operation Sunbeam. The main attraction was a secret device which was bolted to the roof of an armored personnel carrier, a contraption called the The Davy Crockett Weapon System.

The Davy Crockett shell weighed about seventy-six pounds, and it vaguely resembled a watermelon with fins. At thirty-one inches long and eleven inches in diameter, the projectile was too large to fit inside the gun, so it perched on the top while an attached rod was inserted into the barrel. The shell could be fired from a four-inch-wide recoilless rifle which could lob the bomb a little over a mile, or a larger six-inch-wide version which could heave it up to two and a half miles. The launchers were mounted to jeeps and personnel carriers, and each was operated by a three-man atomic squad. The Davy Crockett was also designed to detach from its vehicle, allowing the teams to relocate on foot and dispatch their miniature mutually-assured-destruction from a handy tripod mount.

The Atomic Battle Group was charged with the protection of Europe between 1961 and 1971, and during those ten years 2,100 of the Davy Crockett Weapons Systems were deployed. In the event of a Soviet invasion, these elite squads were trained to deploy themselves in the path of the advancing formations. Once in position, a flurry of mathematics would provide the trajectory and flight time to the targets, and these data would be used to configure the launchers for maximum carnage. A test shot with the integrated 37mm spotting gun would verify the operators’ angle and timing calculations. The three men would then unpack a shell from its carrying case, set the timer knob to detonate the warhead roughly twenty feet above the target, and dial in their preferred yield of ten or twenty tons.

Upon receiving the order to fire, Davy Crockett would leap from its perch with a bang and a cloud of smoke, racing through sky in a long arc to intercept the advancing enemy. The rudimentary atomic bomb did not include an abort feature, so Davy Crockett was committed to destruction once it was en route. Even with the help of the spotter gun and rifled barrel, both of the Davy Crockett launcher designs were somewhat sloppy in their accuracy, so the detonation was likely to be several hundred feet from the target. Moreover, the shells’ relatively small yield didn’t produce a great deal of blast damage even at the highest setting. But the weapon’s tendency to spew radiation over the battlefield made up for its shortcomings as an explosive.

Any person within a quarter-mile radius of the Davy Crockett explosion would face almost certain death. Those within the first 500 feet would be exposed to enough radiation to kill within minutes or hours, even with the protection of tank armor. People at about 1,000 feet from the blast would experience temporary fatigue and nausea which would then pass, but this misleading “walking ghost” condition leads to a painful death after a few days of apparent well-being. Those beyond a quarter-mile would have better chances of survival, though many would require extensive medical care, and perhaps never fully recover from their injuries. Those lucky enough to be more than one-third of a mile from ground zero would be spared most of the harmful effects, but the mutations in their DNA would give them an increased risk of cancer later in life.

The Davy Crockett’s timer allowed a minimum shot distance of about 1,000 feet, but such inept use of the weapon would certainly result in the deaths of the firing team. In most cases, the approaching Soviets would be at least one mile away, leaving the Atomic Battle Group personnel outside of the hazard zone. Even if the launcher’s lack of accuracy resulted in relatively few enemy casualties, the radioactivity from the hail of fission bombs would render a large swath of earth uninhabitable for about 48 hours, allowing time for American and NATO forces to mobilize.

Variations of the W54 warhead found a few other niches during the Cold War, including the Special Atomic Demolition Munition (SADM) which could be simply dropped off at a target and set to explode with a timer. A more powerful 250 ton variant was also used on the AIM-26 Falcon, a guided air-to-air missile. Fortunately these ultra-portable casualty dispensers were never used outside of the Nevada desert.

In addition to being the smallest nuclear device ever developed by the United States, the Davy Crockett also has the distinction of being the last atomic device tested by the US in the open atmosphere. The 1962 test shot at the Nevada Proving Grounds confirmed the effectiveness of the design, and the device’s tiny form factor made it a real crowd-pleaser— or a crowd killer, depending on one’s point of view. With the destructive power of twenty tons of TNT squeezed into a watermelon-sized package, it’s hard to outperform the Davy Crockett in terms of convenient annihilation per cubic inch (CACI). Though its use could have triggered a chain reaction that would have ultimately led to the destruction of humanity, it’s hard not to have a strange kind of fondness for the little feller.

King of the Wild Frontier (excellent Davy Crockett article)




Alex Wellerstein's fantastic nuke blog which I've linked to before:

The Nuclear Secrecy Blog

Within his fantastic Davy Crockett article from July 2012, he said:

I have — after a few weeks of effort, I might add — managed to get the Library of Congress system to cough up Army Field Manual FM23-20, “Davy Crockett Weapons System in Infantry and Armor Units,” which has some great Davy Crockett photographs that I’d never seen before, as well as notes on how you’d go about trying to use this thing.

The LOC has somewhat slow scanners, and somewhat expensive photocopiers, so I’m not going to reproduce the report in full (at least at this time). But it’s a cool thing, and here are my favorite parts.

Apparently he never did release it in full because I can't find a PDF of it anywhere online. It's obviously not classified or they wouldn't have had a copy to give him nor would they have given it to him.

I did find these PDFs available for download while searching for FM 23-20 which I would LOVE to read:

Army Field Manuals

One of Alex Wellerstein's many tweets about nukes, this one funny, on his excellent Twitter feed which I just found even though I've known about his blog for many years!:
Thanks, I have the Dave Crockett song rattling around in my head.
From the comments on Alex Wellerstein's blog:

Ken says:
August 26, 2012 at 4:23 pm

If you were being overrun, shaped charges were carried to destroy the projectile. The launcher was destroyed by thermite grenades. The timer counted down to zero but it would not start the countdown until the projectile was fired. There was no way to start the timer without firing the projectile.

There seems to be a fundemental misunderstanding of the timer. Even if you could set the timer working on the ground, the projectile would not explode. The timer was a safety device to prevent the bomb from going off too early. Please note that the timer was at the base of the rear antenna dome. It controlled when the information from the antenna domes would start to be used. So, the zero setting did have a purpose, was very important and was used in every firing event but it did not cause the explosion. The timer only told the projectile when it could start to calculate it’s height in preparation for exploding. It was not just a “dumb” bomb.

I served a Davy Crockett for 13 months in Korea in every crewman’s position. 1965-66.

Ken says:
August 26, 2012 at 7:37 pm

The projectile passed it’s burst height twice. On it’s way up and again on it’s way down. As a safety, it would not be fully ready to detonate until the rear antenna dome no longer sensed the ground and the timer ran down. The timer was a safety device. For example, if you were in a valley and firing over a mountain, you could not have the projectile sensing the mountain as it could possibly go off as it passed it’s height of burst setting in going over the mountain.

Yes, that was what the HOB switch was for. When the radar said it was the correct distance from the ground as set by the HOB switch, it would detonate. The switch had two settings. Each was set to one specific height. We always set it to “High” in practice because, in a war, special permission had to be granted to set it to “Low”. In the projectile in 1966, there was no provision to change the yield. The yield was set at the armory inside the projectile. We could not change it.

Ken says:
August 28, 2012 at 8:23 pm

I was thinking about the DC weapons system and thought I could expand on some of the timer info. The timer ONLY armed the fuse at the end of the time setting. Each mark was 1/2 second. It had to be set for at least one second or the fuse would never arm. On the “S” (safe) mark, the fuse could not be armed. A spanner wrench came with the projectile. One side had two projections to set the timer and the other side had a small prong with a screwdriver tip to set the HOB and Arm Safe switches.
No calucations were required to figure out the timer setting. Once you had figured out the range, a book with tables in it was consulted and it told you the setting. The crew man that figured out the direction, range and corrections to the guns (the DC and the 37mm spotting round) was called “Computer”. This was the actual Army designation – not a nickname. We had NO actual computers. The gun elevation for the spotting round was different than the DC round. When the 37mm was on target the gun would be “superelevated” to the much higher elevation required by the DC round. The Computer would figure the superelevation by again using the charts in a book. I personally think the need to change the elevations caused the gun to be somewhat less accurate. But then, how accurate do you have to be when firing nuc’s?

Ken says:
August 28, 2012 at 7:41 pm

“The way the gun works is that you put a huge tube of conventional propellant behind the projectile, and then a long “launching piston.” The piston is attached to the nuke. When the conventional propellant goes off, it sends the piston flying, which in turn transfers that force to the projectile.”

Just some thoughts about the launching piston. It was attached to the projectile by two bayonet slots. When the gun was fired, part of the propellent gas would go through a strainer at the bottom of the piston and the pressure between the piston and projectile would separate them about 13 feet in front of the mouth of the gun. What’s interesting was that the piston would then begin to tumble and fall to the earth well before the target area. As there would normally be some of your own troops between the DC crew and the target, you could kill or injure your own troops! They would be warned over the radio when to take cover – not only as protection from the exploding nuc, but from the piston.
I am wondering could this bomb size be used for Project Orion or similar project in space? Was this a pure fission bomb?
GREAT QUESTION which led me to look for and find this:

In late 1958 to early 1959, it was realized that the smallest practical vehicle would be determined by the smallest achievable bomb yield. The use of 0.03 kt (sea-level yield) bombs would give vehicle mass of 880 tons. However, this was regarded as too small for anything other than an orbital test vehicle and the team soon focused on a 4,000 ton "base design".

The optimal Orion drive bomblet yield (for the human crewed 4,000 ton reference design) was calculated to be in the region of 0.15 kt, with approx 800 bombs needed to orbit and a bomb rate of approx 1 per second.

The W54 warhead used in the following systems were capable of these yields in these variants:

There were four distinct models of the basic W54 design used, each with different yield, but the same basic design. These were:
SO, W54-based warheads (a fusion boosted warhead which probably explains the huge yield range - less or ZERO D/T gas, less yield) could have been EXACTLY what they had been thinking about using for Orion. The Orion program was ongoing at EXACTLY the same time the W54 was developed and deployed. In everything I've seen about Orion, they were always super tight lipped about the warhead tech and even made a specific point of saying that.


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