Manhattan project completed slightly quicker.

What would happen if the atomic bombs were ready to deploy in May?
This would allow usage of the atomic bombs before the Soviets can move their troops to take on the Japanese.
What effect would a slightly earlier end to ww2 have on the world?
 
...What effect would a slightly earlier end to ww2 have on the world?
Does it end slightly earlier?
Whether it was the bombs, the Russians, or a combination of the two, together is something which gets tossed around semi-regularly in threads about the end of WW2 in the post-1900 forum (and occasionally in nuclear weapon related threads in political chat.)
 
Summary of Target Committee Meetings

May 10 and 11, 1945

Declassified government document

Memorandum from Major J. A. Derry and Dr. N. F. Ramsey to General L. R. Groves

Status of Targets

A. Dr. Stearns described the work he had done on target selection. He has surveyed possible targets possessing the following qualifications: (1) they be important targets in a large urban area of more than three miles diameter, (2) they be capable of being damaged effectively by a blast, and (3) they are likely to be unattacked by next August. Dr. Stearns had a list of five targets which the Air Forces would be willing to reserve for our use unless unforeseen circumstances arise. These targets are:

(1) Kyoto—This target is an urban industrial area with a population of 1,000,000. It is the former capital of Japan and many people and industries are now being moved there as other areas are being destroyed. From the psychological point of view there is the advantage that Kyoto is an intellectual center for Japan and the people there are more apt to appreciate the significance of such a weapon as the gadget. (Classified as an AA Target)

(2) Hiroshima—This is an important army depot and port of embarkation in the middle of an urban industrial area. It is a good radar target and it is such a size that a large part of the city could be extensively damaged. There are adjacent hills which are likely to produce a focusing effect which would considerably increase the blast damage. Due to rivers, it is not a good incendiary target. (Classified as an AA Target)

(3) Yokohama—This target is an important urban industrial area which has so far been untouched. Industrial activities include aircraft manufacture, machine tools, docks, electrical equipment and oil refineries. As the damage to Tokyo has increased additional industries have moved to Yokohama. It has the disadvantage of the most important target areas being separated by a large body of water and of being in the heaviest anti-aircraft concentration in Japan. For us it has the advantage as an alternative target for use in case of bad weather of being rather far removed from the other targets considered. (Classified as an A Target)

(4) Kokura Arsenal—This is one of the largest arsenals in Japan and is surrounded by urban industrial structures. The arsenal is important for light ordnance, anti-aircraft and beach head defense materials. The dimensions of the arsenal are 4100’ X 2000’. The dimensions are such that if the bomb were properly placed full advantage could be taken of the higher pressures immediately underneath the bomb for destroying the more solid structures and at the same time considerable blast damage could be done to more feeble structures further away. (Classified as an A Target)

(5) Niigata—This is a port of embarkation on the N.W. coast of Honshu. Its importance is increasing as other ports are damaged. Machine tool industries are located there and it is a potential center for industrial despersion [sic]. It has oil refineries and storage. (Classified as a B Target)

(6) The possibility of bombing the Emperor’s palace was discussed. It was agreed that we should not recommend it but that any action for this bombing should come from authorities on military policy. It was agreed that we should obtain information from which we could determine the effectiveness of our weapon against this target.

B. It was the recommendation of those present at the meeting that the first four choices of targets for our weapon should be the following:

a. Kyoto

b. Hiroshima

c. Yokohama

d. Kokura Arsenal


It's not ASB level work to speed up Oak Ridge by six to nine months.

Truman removed Kyoto and Tokyo, not wanting to atom bomb the Capital or former. Kokura moved up, and Nagasaki added.

Oak Ridge online earlier might mean a 2nd test after Trinity to test viability of using U-235 with implosion than with gun devices, as implosion is so much more efficient.

Little Boy used over 4 Critical Masses worth of bombs, had the been used in Fat Man style bombs instead

Now in May, these cities hadn't been Damaged that much by firebombing

Amagasaki
Fukuoka
Hbe
Moh
Nishinomiya
Osaka
Sendai

and could be targets.

I don't think the Japanese will wait for the Soviets to attack by time six cities have been glassed, one every 6-12 days
 
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Does it end slightly earlier?
Whether it was the bombs, the Russians, or a combination of the two, together is something which gets tossed around semi-regularly in threads about the end of WW2 in the post-1900 forum (and occasionally in nuclear weapon related threads in political chat.)

There was a third factor present in August. In July the estimates for the 1945 harvest were made available to the cabinet. The rice harvest estimate in this is usually cited as 'catastrophic'. That item may be hyperbole, but the various analysis or judgements I've seen of the situation are not favorable for the Japanese ability to resist. No matter how one parses it out it looks like the overall caloric allotment in the food rations would fall significantly, from their already inadequate levels.

This harvest report was not close to ready in May, the raw data for the various crops not yet existing or processed. Neither was it clear how much further imports would fall in the next few months. The latter was much clearer after another two months of failure to ship in adequate reserves from the mainland. Neither was the Red Army remotely ready to attack on the desired scale in May. Of course a attack could have been made, but it would have been mostly attritional battles along the borders, with far less ability to advance into the interior of Manchuria or Korea.

What would happen if the atomic bombs were ready to deploy in May?
...

This can be read as either just the two bombs actually used, or if the same production schedule of OTL is advanced 90 days. In that latter case we are not just looking at two bombs, but at least one more Plutonium bomb ready for use in less than ten days after the second of OTL was used. So, in less than a month Japan is hit by three such weapons in less than three weeks. & remember the firebombing attacks did not cease, and the smaller air raids on the transportation system, the airbases, the naval bases, the Army logistics depots, the smaller industrial sites, all continued. The USN was participating in these, with the carriers raiding the ports and sinking any remaining cargo and war ships.

Its not as if all other attacks ceased with the use of the two atomic weapons. The air assault was being ramped up in all aspects and was planned and ready to continue escalating as August rolled on into September & October. Set the atomic weapons ahead to May and nothing need change with the rest of it. The fire bomb attacks continue, the smaller more precise Navy and Air Force raids ramp up. The subs continue sinking ships at sea. Food still rots on the docks on the Asian coast.

The escalating attack applies to the atomic weapons as well. Rhoades in 'The Making of the Atomic Bomb' estimates at least five more bomb cores would have been shipped to Tinian by November, or five more bombs in the 90-100 days after the first was dropped. Thats the low estimate. Other estimates vary widely, with the original projections for the design of the Haniford Plutonium production facility being twice that of Rhoades estimate. While problems and delays from the hasty fastback construction, and inexperience abounded, its not ASB territory to speculate six or seven Plutonium bombs could be available in 90 to 120 days from 8 May. Then there is the question of additional Uranium bombs. A decision was made to complete just one Uranium bomb, but the wherewithal to build more was present.

Bottom line here is: Japan would have been subject to the same increase in conventional bombing and other direct attack as OTL over the next 90 days from 8 May to 8 August. AND, at least six atomic weapons could have been used as well. How the cabinet, emperor & the Zaibatsu would have responded to this? Draw your own conclusions.
 
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Then there is the question of additional Uranium bombs. A decision was mae to complete just one Uranium bomb, but the wherewithal to build more was present.

Although a series of improvements for the implosion bomb were envisioned and under development at Los Alamos even before Trinity, the first nuclear test, the end of the war had derailed these efforts. With the Cold War rapidly developing, an urgent need was felt to bring these improvements to the U.S. weapon stockpile.


On 27 June 1947 President Harry Truman authorized a new test series for weapons development for the following year. Operation Sandstone was conducted at Enewetak Atoll in the Marshall Islands in 1948 to test the first new weapon designs since World War II. The massive operation involved 10,200 personnel.

The original Fat Man pit design used a Christy solid plutonium core, surrounded by a close fitting natural uranium tamper. The Sandstone devices all replaced the contiguous tamper-core approach with a "levitated core" in which the core was suspended within a larger hollow space within the tamper so that a gap existed between them. The collision between the tamper and core would create more efficient compression of the core than the explosive-driven shock in the watime design. They apparently retained a solid core however.

These devices also abandoned the use of a pure plutonium core since oralloy (uranium highly enriched in U-235) production exceeded plutonium production by a factor of over 3-to-1. The first test, X-Ray, used a composite oralloy-plutonium core. Both Yoke and Zebra used an all oralloy core. The pits (tamper plus core) for all three devices weighed about the same.

Other tested features included:

  • varying the tamper thickness (which had been fixed at 7 cm in earlier devices)
  • varying the amount of fissile material in the core
  • the effect of using a "minimum strength" polonium-beryllium Urchin neutron initiator.

Previously, Urchins containing the full load of 50 curies of Po-210 had been used in tested bombs. Guidelines permitted the use of initiators with as little as 12 curies, but the adequacy of these had never been put to an actual test. Given the very short 138.4 day half life of Po-210, this was an important question for maintaining a ready stockpile.

Although the Sandstone tests continued to use the Mk 3 implosion system, they proof tested components that led to the fielding of the Mk 4 bomb. The Mk 3 bomb used for the Sandstone devices was 60 inches in diameter and weighed 10,500 lb total; the explosive, core and firing system weighed 7,600 lb.

Both the principle of levitation and the use of oralloy-plutonium composite cores had been under development at Los Alamos during the war. If it had continued into the fall of 1945, both of these innovations would have been introduced to increase the size and efficiency of the stockpile. Now, the confrontation with the Soviet Union impelled the inclusion of these innovations in deployed weapons. The results of Sandstone led to the immediate stockpiling of both X-Ray and Zebra core designs, replacing all other designs. Taken together, this lead to an immediate increase in total stockpile yield of 75%.


Test: X-Ray
Time: 18:17 14 April 1948 (GMT)
0617 15 April 1948 (local)

Location: Island Engebi ("Janet"), Enewetak Atoll
Test Height and Type: 200 foot Tower Shot
Yield: 37 kt

The X-Ray device used a uranium-plutonium composite Type B levitated pit. The uranium-to-plutonium ratio by weight was on the order of 2:1 or greater. Efficiency of utilization of the plutonium in this core was around 35%; uranium utilization was in excess of 25%. Taken together this indicates a core containing about 2.5 kg of Pu, and 5 kt of U-235. This was the highest yield device tested to date.

Test: Yoke
Time: 18:09 30 April 1948 (GMT)
0609 1 May 1948 (local)

Location: Island Aomon ("Sally"), Enewetak Atoll
Test Height and Type: 200 foot Tower Shot
Yield: 49 kt

The Yoke device also used an all-oralloy Type B levitated pit. Yoke was the highest yield device tested, a record it kept until 1951. Despite its high yield, it was regarded as an inefficient device.

Test: Zebra
Time: 18:04 14 May 1948 (GMT)
0604 15 May 1948 (local)

Location: Island Runit ("Yvonne"), Enewetak Atoll
Test Height and Type: 200 foot Tower Shot
Yield: 18 kt

The Zebra device also used only highly enriched uranium in the levitated pit. Despite its lower yield than Yoke, it apparently had superior efficiency (at least for its size).


http://nuclearweaponarchive.org/Usa/Tests/Sandston.html

Now with continual bombing, it's likely that the composite or pure U-235 cores would be used in Fat Man style bomb casings, and yields were far higher with the other improvements that were thought of, even before Trinity was first tested
 
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If the bomb Trinity Test takes place in May 1945 it is a big game changer.
First off this more good news for the western Allies. First the Germans surrender and now the Americans have a super bomb ready to use. For both Truman
And Churchill there is the chance that Japan can be defeated without an invasion.
There is now the possibility that a Potsdam type first meeting with the Soviets will be held AFTER successfully detonating the bomb or bombs. Of course Stalin will know the bomb is ready because of his spies but now he will have seen the real thing in action. Truman might bring a copy of a film showing Trinity and an actual bombing with him.
Truman will be pushed to bring about a quick decisive end of the Pacific war right on the heels of VE Day. In May the Battle of Okinawa is still going strong. I think the Joint Chiefs will call for building up a stockpile of atomic bombs and unleashing them on the Japanese. There will be no debate over warning the Japanese. The clear intent will be to nuke Japan to the peace table.
 
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1. Peace might have been more achievable; US had demanded 'unconditional surrender'; ITL after the Potsdam declaration (late July) restated that demand Japan did respond but presented four conditions (incl. no occupation, no trials conducted by allies. and preservation of imperial institution). In the end Japan conceded everything but the emperor - which US agreed to (without formally putting it in writing); but negotiations were conducted with Russia as intermediary and Russia stalled them (since they wanted Manchuria). There were only a couple weeks between Potsdam and Hiroshima

2. So with the Bomb in his pocket, its possible that Truman might have taken more diplomatic initiative in May; and that Japan might have (informally) conceded more sooner and with less interference from Russia.

3 But then again maybe -as ITL- it would have taken two bombs to force the army minister to agree. I think after Hiroshima he said something like 'the Americans couldn't have more than one'. But then after Nagasaki he more or less said 'it's over'.
 
One thing that delayed the deployment was the need for 60-65kg of U235 for the gun-type. That took about 6 months to produce. If the need for the implosion-type for use with Plutonium was realized sooner, and the implosion device developed sooner, you don't need 6 months of U production for the first bomb, only a quarter of that. So you would have enough U235 for a implosion device by Mid February, and another every 6 weeks after that on the original production schedule. That's Trinity in Late Feb-Mid March with little actual change to fissile production, just a faster tech development on the implosion design.

FWIW, a implosion design with the same 60-65kg of U235 used in LB was tested, it resulted in a 500kt detonation, the largest pure fission detonation IIRC.
 
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