Why didn't we focus on a gun-type nuclear weapon only?

You, and he, seem to have missed my point. Had the atomic bomb program focused entirely on enriched uranium there would have been more available because none would have been diverted to the manufacture of plutonium.
Not really. While there might have been more HEU there's have been far fewer actual weapons.

There's a huge difference between the natural uranium used in the Hartford reactors (with 0.7% U235) and the HEU used in the MK1 (>80% U235). The resources to construct the Hanford complex wouldn't have helped much with uranium enrichment.
Hell even if you assumed a 50/50 split in resourcing between the uranium separation and plutonium production aspects of the project and assumed that dropping the plutonium aspect completely doubled the production of HEU there's still only have been two bombs by JUL1945 and two more by the end of the year, rather than a total of 22 weapons.

And such assumptions simply wouldn't be true. Take the dollar costs of the Manhattan Project for example.
Of the roughly 1.9 billion dollars (1945 dollars) the Oak Ridge isotopic separation facility consumed 1.19 billion. More specifically:
  • Gaseous Diffusion Plant (K25) $512M
  • Electromagnetic Separation Plant (Y12) $478M
  • Thermal Diffusion Plant (S50) $16M
  • Engineer Works, headquarters and utilities $156M
  • Laboratories $27M
While the Hanford facility cost only $390 million and 'special materials' (graphite, uranium, boron, special alloys, and plastics, silver, et cetera but excluding heavy water) cost $103M.

Dropping the uranium bomb in favour of a larger plutonium project (assuming sufficient natural uranium was available for the additional reactors) would have been a more economic path.

Of course this is with hindsight... We know the plutonium bomb concept is viable.
 
No doubt, but certainly more than the one uranium bomb that there was historically.
Unlikely. As I pointed out the cost of a duplicate isotopic separation facility was far higher than the plutonium complex. Moving those resources probably wouldn't have produced enough HEU for a second bomb in time.
If this path was followed the US would be running a monumental bluff after the one or two uranium bombs were used.
 
They were anyway.
No.

Historically the first three bombs were ready in early July 1945 (Gadget and Little Boy) and mid July (Fat Man). The fourth bomb (the "Demon Core") would have been usable by 19AUG1945, the fifth by 01SEP1945, the sixth through eighth before the end of September followed by three or four more in October, et cetera, et cetera, et cetera.

The atomic bombing of Japan could have continued, at the rate of approximately three bombs per month, for the rest of 1945 and accelerated (as the new Hanford complex came on-stream) in 1946 to approximately one bomb per eight days, with more rapid production if this was seen as necessary and new developments such as the MK4, composite pits (not wasting uranium on MK1s), series production (rather than hand assembly) and more.

No bluff.
 
Hanford.
Specifically the breeder reactors and plutinium separation facilities at the complex.
Even more specifically the B Reactor (aka 105-B) there which was the world's first plutonium production reactor; it used 180 tonnes of natural uranium, graphite moderation and water cooling and ran at 250MW thermal. It was constructed between AUG1943 and SEP1944, went critical that month and produced the first plutonium in November. Two more reactors ("D" and "F") were operating by FEB1945. The first plutonium was shipped to the Los Almos complex on 05FEB1945.

More fundamentally the plutonium is produced by nuclear transmutation of uranium; U238 atoms absorb a neutron each and then successively emit two beta particles becoming plutonium 239 (and an occasional atom of Pu240 much to people's irritation when a second neutron is absorbed). After a period in the reactor the fuel tubes are removed and very carefully chopped up, the fissionable material dissolved in nitric acid and the plutonium separated chemically. At Hanford this was done in the 221-T building.

Wait by 180 tonnes of this material, how much of it was Uranium? Couldn't they simply put focus into factories on producing as much HEU as possibly with the LEU, and stop all advancements of the Manhattan Project, focusing on simply converting whatever uranium they have on their hands into weapons grade ready for a gun type? Wouldn't this make more nuclear weapons instead?
 

Wendigo

Banned
The Gun type, as noted, was extremely limited, both in potential numbers and, perhaps more importantly, in yield.

It was more or less a math problem. If the U.S. had been forced to wage an actual campaign with nuclear weapons, instead of simply using them to finish off an opponent that was ready for a knockout blow (which actually was a combination of two nuclear jabs and Soviet invasion uppercut), it would not have been possible using urainium weapons exclusively.
So no Soviet invasion means Japan shrugs off the nukes and Operation Downfall ensues?
 

CalBear

Moderator
Donor
Monthly Donor
So no Soviet invasion means Japan shrugs off the nukes and Operation Downfall ensues?
Potentially.

By mid-July about the only people eager for Downfall were on MacArthur's staff. Intel kept finding more IJA strength, signs of even more kamikaze aircraft, with the prospects for Okinawa writ large pressing ever harder on the folks in DC. That said, MacArthur had considerable influence.

IMO Truman tells MacArthur to go have a Coke and a smile, takes Marshall's and Leahy's advice and blockades/burns Japan to death.
 
and stop all advancements of the Manhattan Project, focusing on simply converting whatever uranium they have on their hands into weapons grade ready for a gun type? Wouldn't this make more nuclear weapons instead?

There wasn't a shortage of Uranium. Bottleneck was the Calutrons at Y-12. Gaseous enrichment was improving at K-25, and postwar Y-12 was mostly shutdown and additional stages at new plants, K-27, K-29, K-31 and K-33 to make HEU. K-27 plant was online in February 1946

Thru 1946, Oak Ridge made 571kg of 90-96% HEU and 905kg of 20-70% U-235.

Starting with the Mk-3 bomb, they used hollow pit composite cores, 2.5kg of Pu, and 5kg of HEU
 

Delta Force

Banned
Wait by 180 tonnes of this material, how much of it was Uranium? Couldn't they simply put focus into factories on producing as much HEU as possibly with the LEU, and stop all advancements of the Manhattan Project, focusing on simply converting whatever uranium they have on their hands into weapons grade ready for a gun type? Wouldn't this make more nuclear weapons instead?

Uranium enrichment capacity wasn't easily scaled at the time. The best process using Manhattan Project technology would have been to build a gaseous diffusion facility akin to K-25 to provide enriched feedstock to an electromagnetic separation plant akin to Y-12. Those facilities are very expensive to build, require strategic materials, and require vast amounts of energy. K-25 and the civilian Eurodif facility built in France in the 1970s both required around 3,000 megawatts of power to operate. The United States nuclear power program was built in federal utility areas and used power from the Tennessee Valley Authority and Bonneville Power Administration to run nuclear facilities, while the French used 3 of the 4 units at Tricastin to power Eurodif.
 
K-25 and the civilian Eurodif facility built in France in the 1970s both required around 3,000 megawatts of power to operate. The United States nuclear power program was built in federal utility areas and used power from the Tennessee Valley Authority and Bonneville Power Administration to run nuclear facilities, while the French used 3 of the 4 units at Tricastin to power Eurodif.

Eurodif’s Georges Besse plant with 1400 stages, uses 2000MWe from my notes.

That's a lot of power. Hoover Dam is rated for 2080MWe

K-25 at Oak Ridge had 3122 stages operating in 1945, with additional plants-- K-27, K-29, K-31 and K-33, for a total of 5,098 stages
estimates I come across was 7300MWe power consumption
 
Wait by 180 tonnes of this material, how much of it was Uranium? Couldn't they simply put focus into factories on producing as much HEU as possibly with the LEU, and stop all advancements of the Manhattan Project, focusing on simply converting whatever uranium they have on their hands into weapons grade ready for a gun type? Wouldn't this make more nuclear weapons instead?
Nope. That 180t was unenriched natural uranium, with around 0.7% U238. Enriching the 64kg of uranium used in the 'Little Boy' MK1 bomb (about 80% U235) took years. First the plants needed to be constructed, at immense cost, with much of the engineering having to be designed from scratch. Handling uranium hexafluoride on such a scale was unheard of and itself required new materials. Three different approaches (electromagnetic, gaseous diffusion and thermal diffusion) were attempted as it wasn't known which would be most effective.
Of course once the process was developed it was improved greatly over the years but until the 1980s and the development of large IC fabs the isotopic separation plants were the largest, most expensive and most complex industrial facilities in the world.
 
I believe that once the plutonium-based atomic bomb was successfully tested, it was decided to concentrate on that weapon design because of the growth potential for higher explosive yields. I believe by 1950, improved "implosion" designs increased the explosive yield to near 60 KT.

Interestingly, the gun barrel type nuclear weapon was tried out again with the 280 mm atomic cannon shell during the Upshot-Knothole Grable test, which had an explosive yield of 15 KT. Destruction proved to be larger than anticipated due to the secondary shock wave effect of the explosion, mostly because of the very low altitude of the explosion (only 500 feet off the ground).
 
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