Uranium from USS Indianapolis captured by Japanese 28 July 1945

[trurle]

Chapter 1. The OP.
USS Indianapolis (that time on a secret mission to deliver uranium and parts of nuclear bomb to North Marian Islands) has developed an rudder trouble 25 July 1945, just few hundred kilometers short of her destination, leaving her uncontrollable and running a short cycles. Initially captain was reluctant to break radio silence, being assured what the damage to rudder will be fixed before daybreak. The repairs were half completed, then the ship was spotted by Japanese submarine Ro-50, torpedoed, heavy listed and stopped dead in the water. Utilizing a dead zone created by Indianopolis heavy list, the Ro-50 strafed Indianapolis deck and superstructure at will for several hours by 25mm cannons, until full exhaustion of ammunition, irreparably disabling all her radio equipment, along with other minor damage.

At daybreak, Ro-50 has dived and maneuvered away to avoid expected US planes. When night came, the Japanese captain was very surprised to find Indianapolis still on the same position, with apparently no crew aboard. He then dared for a desperate adventure and launched a boarding party, as his load of torpedoes was completely spent.

In flag officer cabin, Japanese found a strange metal drum and with a great difficulty rappelled it to the submarine`s deck. Also, they found few badly wounded survivors, left behind by fleeing crew of Indianapolis. Unknown to them, one of the was the radiologist Furman, who did knew some context of the mysterious drum.

After an arduous and risky voyage, Ro-50 has arrived to Yokosuka 3 August 1945, carrying American captives and now severely crumpled drum. The captives were interrogated then, brutally and with hurry. By the 4 August 1945, Japanese did know they captured the specially made radioactive materials for the new decisive weapon.

P.S. This is severely altered OP addressing plausibility critics below.

P.P.S. The Japanese have never realized their exceptional luck - every person on Indianapolis who intended to dump be fissile material abroad or load it in lifeboat was killed or disabled, by initial torpedo explosion, secondary explosions or by Japanese small-caliber shelling.

 

[calvinhobbesliker]

Well, the US still has the Fat Man Bomb and a few more coming. The Japanese will not have the time to take advantage of their capture.

 

[wcv215]

So, why is the Indianapolis not shooting back during this strafing? And why doesn't it break radio silence when it becomes clear the submarine is going to continue attacking with its gun?

 

[COMV99]

I'm not sure there was enough uranium for a full bomb, but I'm uncertain. Torture is also really ineffective. If you pushed and died to extract information in only a few days, you would probably kill most people instead. I also see no reason for the submarine to just simply sink it. They have no idea it's carrying nuclear material. Sending a destroyer to capture the ship seems like a really strange move as well.

 

[COMV99]

So, why is the Indianapolis not shooting back during this strafing? And why doesn't it break radio silence when it becomes clear the submarine is going to continue attacking with its gun?

It doesn't shoot back because it's listing to one side, so the guns can't depress down and shoot the submarine.

 

[wcv215]

It doesn't shoot back because it's listing to one side, so the guns can't depress down and shoot the submarine.

But even then surely the captain wouldn't be stupid enough to just sit and take the shots rather than radioing for help. I know they're on a secret mission, but if they never make it to their destination its sure to fail.

 

[COMV99]

But even then surely the captain wouldn't be stupid enough to just sit and take the shots rather than radioing for help. I know they're on a secret mission, but if they never make it to their destination its sure to fail.

I agree on this point, this scenario has too many contrivances. I'd rate this as ASB. It does seem like an interesting ASB, if the point is giving Japan a nuclear weapon.

 

[trurle]

So, why is the Indianapolis not shooting back during this strafing? And why doesn't it break radio silence when it becomes clear the submarine is going to continue attacking with its gun?

Larger guns could not be be elevated to compensate for 60-degrees list. Smaller AA guns, up to 40mm Bofors, were fired, but crews had a big problems getting to positions, aiming guns and feeding ammunition in such a situation (when walls become flooring). Japanese gunners, acting in ideal conditions, has managed to get fire superiority even with their meager 25mm guns.

Regarding calling for help by radio, Indianapolis tried. Attempt just took too much time. By the moment the radio operator has received an order to set transmit key, the antennas were badly damaged, first by water pillar from torpedo. Then come power outage, then damage from gunfire, then radio operator hand slipped and he fell in water, then US sailors searched for another radio operator, who got shot while trying to get to radio room etc..

 

[trurle]

I'm not sure there was enough uranium for a full bomb, but I'm uncertain. Torture is also really ineffective. If you pushed and died to extract information in only a few days, you would probably kill most people instead. I also see no reason for the submarine to just simply sink it. They have no idea it's carrying nuclear material. Sending a destroyer to capture the ship seems like a really strange move as well.

Well, if you believe the torture is ineffective, then you should try yourself how to be tortured..

The submarine did not sink Indianapolis because she was unable - she spent for the damaging volley her last torpedoes.

Sending a destroyer was the action to minimize risk (can rapidly disengage and escape if some rescue forces will appear) while providing some decent towing capability. Japanese at that stage of war were clinging for any hope, and hope to salvage something important from strange-behaving cruiser may motivate equally strange decisions.

Regarding the crew knowledge - some of officers definitely knew they carry something top-secret, irreplaceable and important. And knew the compartment number.

The rest is the mental exercise. You have some mysterious parts of utmost military importance, which fit into cylindrical shell if assembled. Of course, it is bomb! And of superb power.

 

[marathag]

By the morning of 4th of August, 1945, Japanese had the nuclear bomb. Or at least the parts to build it.

No, not all of it.

The Indianapolis carried 9 U-235 Rings (S) that when assembled, made the outside part of the assembly. The smaller rings (H) that would fit inside those, were flown in on three separate C-54s flights, with each carrying two. All flights arrived at Tinian by July 28

 

[trurle]

No, not all of it.
The Indianapolis carried 9 U-235 Rings (S) that when assembled, made the outside part of the assembly. The smaller rings (H) that would fit inside those, were flown in on three separate C-54s flights, with each carrying two. All flights arrived at Tinian by July 28

I knew. The Japanese attempts to produce a bomb from incomplete set is a part of the story. By the way, outer rings together are exceeding a critical mass. Of course, reduced mass bomb would be significantly less powerful.
P.S. I see this topic attract some interest among readers, so will add next chapter soon.

 

[Cockroach]

The Japanese navy had been pushed out of both the Philippians, Guam and Marianas Islands by July 1945. Taiwan is the closest place likely to have any warships available to intercept and tow the crippled Indianapolis.

Thing is, it's c. 1000 nautical miles to there... For a Akizuki class DD going top speed that's 30 hours to get into position, likely longer in practice (maintaining top speed in anything other than light speed is difficult for a DD sized vessel; running at high speed drastically reduces endurance; etc.). So, right of the bat your timeframe is at least one day shorter than possible (mid-day-ish on the 28th rather than evening on the 27th) ... a day in which the Yanks can either get their radios working again or possibly correct the list and get at least some of the secondary/heavy AA battery back in action (raising a significant risk for the destroyer).

Towing a badly damaged ship? It took the best part of two weeks to tow USS Canberra from near Taiwan back to Ulithi... 1200-1300 NM depending on precise details of location. That gives a speed of between 3 and 5 knots depending on how much down time before starting the tow you allow. The shortest distance from Indianapolis's OTL sinking location to any of the Japanese home islands is about 1100-1200 NM...So we can expect a similar sorta timeframe. That is, plenty for the allies to realize something is going on and try to intercept the operation.

Finally, while Indianapolis carried uranium for Little Boy it takes rather more than just a critical mass of Uranium to get a proper boom. Whacking two lumps of uranium metal together to get critical mass generally isn't enough to get a full on high yield nuclear explosion... you need the damn things to actually stay together until you get enough neutron flux to generate a rapid and violent chain reaction. Given the heat, pressure and sundry forces generated by the reaction will tend to try to push the chunks of uranium back apart getting things to stay together long enough to get a proper bang actually requires rather complex engineering (gun system in Little Boy, implosion system in Fatman). Otherwise you end up with something like the 'Demon Core'... horribly irradiates everyone within a few dozen meters but no big boom. I doubt Japanese efforts towards developing an A-Bomb were ina position to solve that side of things in 1945 even if a critical mass of uranium fell into their laps.

 

[trurle]

Chapter 2. The understanding.
11 August 1945, Tokyo
Imperial General Headquarters Liaison Conference.

- Suzuki-san[1], thank you for bringing your pet professor. Figurally speaking, we measured the depth of our grave. But still have no idea how to get out. The recent bombing of Hiroshima was perfectly coordinated with the Soviet offensive, and i am afraid this is only the beginning of the end. - prince Yasuhito put the pointer on desk besides a map and sat down - Any ideas?
- I seen the drawing. - the Anami [3] did not attempted to stand before speaking. - We theoretically can fit the contraption under H8K, and detonate it by explosively pushing ring into makeshift squeeze-bore adapter. The size is just like normal aerial torpedo. If we pull out all propulsion. But..if i understood correctly, the more mass we place around narrow end, the stronger it will explode. Unfortunately, we also risking the thing will explode just because of proximity to water, even if not compressed. At least that stability margin experiment with electrostatic field meter was..frightening. Everybody here seen the photos how that technicians died, and the ring has just heated, not exploded. Therefore, i have better idea. Let`s put it in larger, 53cm torpedo from submarine. We will reduce the risk of accidental explosion, make intended explosion amplified by mass of water, and also will have some stand-off capability. You know, how unreliable become kamikaze pilots in last weeks.

Prince Yasuhito nodded slowly.
- I will handle this. Personally. After all, this is a weapon what can decide the outcome of war.

[1] Kantaro Suzuki - prime minister of Japan at that time. Most prominent public figure the commoner can realistically reach with some project
[2] Prince Yasuhito - younger brother of Emperor Hirohito. Prince Yasuhito was known to have affinity for risky adventures and cruelty. Although nobody catch him red-handed IOTL..
[3] Korechika Anami - war minister of Japan at that time. Had some expertise in aviation, and was known for his strong anti-surrender attitudes. IOTL, committed suicide 15 August 1945.

 

[trurle]

The Japanese navy had been pushed out of both the Philippians, Guam and Marianas Islands by July 1945. Taiwan is the closest place likely to have any warships available to intercept and tow the crippled Indianapolis.

Thing is, it's c. 1000 nautical miles to there... For a Akizuki class DD going top speed that's 30 hours to get into position, likely longer in practice (maintaining top speed in anything other than light speed is difficult for a DD sized vessel; running at high speed drastically reduces endurance; etc.). So, right of the bat your timeframe is at least one day shorter than possible (mid-day-ish on the 28th rather than evening on the 27th) ... a day in which the Yanks can either get their radios working again or possibly correct the list and get at least some of the secondary/heavy AA battery back in action (raising a significant risk for the destroyer).

Towing a badly damaged ship? It took the best part of two weeks to tow USS Canberra from near Taiwan back to Ulithi... 1200-1300 NM depending on precise details of location. That gives a speed of between 3 and 5 knots depending on how much down time before starting the tow you allow. The shortest distance from Indianapolis's OTL sinking location to any of the Japanese home islands is about 1100-1200 NM...So we can expect a similar sorta timeframe. That is, plenty for the allies to realize something is going on and try to intercept the operation.

Finally, while Indianapolis carried uranium for Little Boy it takes rather more than just a critical mass of Uranium to get a proper boom. Whacking two lumps of uranium metal together to get critical mass generally isn't enough to get a full on high yield nuclear explosion... you need the damn things to actually stay together until you get enough neutron flux to generate a rapid and violent chain reaction. Given the heat, pressure and sundry forces generated by the reaction will tend to try to push the chunks of uranium back apart getting things to stay together long enough to get a proper bang actually requires rather complex engineering (gun system in Little Boy, implosion system in Fatman). Otherwise you end up with something like the 'Demon Core'... horribly irradiates everyone within a few dozen meters but no big boom. I doubt Japanese efforts towards developing an A-Bomb were ina position to solve that side of things in 1945 even if a critical mass of uranium fell into their laps.

I was thinking of a sort of setting where Keiaki will be used for shuttle supply service between Tokyo and Chichi-jima before been called for tow. Japanese used destroyers sometimes for such risky front-line supply. Chichi-jima to Tinian distance about 700 nm, smaller than your estimate of 1150 nm, therefore arriving at evening of 27th is theoretically possible. In best case, Keiaki would be laden full with fuel intended for submarines on Chichi-jima base, so can afford very uneconomical run.
For towing, i assumed 10 knots speed..well, it may be on optimistic side, but necessary for the purpose of making the interesting plot. Go slower (3-4 knots as you properly suggested) and Japan will surrender even before Indianapolis will arrive.

Regarding makeshift bomb (or, to be exactly, nuclear torpedo) the Japanese deviced, see previous post. Basically, they hybridized "little boy" and "fatman" designs (without really knowing the internals of "fatman"), producing the "little fatman" design, just making order-of-magnitude estimations and engineering guesses about how much unstable the rings must be for practical weapon.

And they have their equivalent of "demon core" incident to learn.

 

[Purity of Violence]

Why doesn't Ro-50 fire more torpedoes into Indianapolis until she sinks?

 

[trurle]

Why doesn't Ro-50 fire more torpedoes into Indianapolis until she sinks?

Because she spent majority of her torpedoes earlier on the another target of opportunity. It is outside of plot, but likely all that torpedoes missed. Submarines of Kaichu class (including Ro-50) are slow underwater, and have a difficulty getting into a proper intercept position, therefore most of torpedoes were launched at extreme range. That submarine property (slow underwater speed and small underwater endurance) is essential for plot - to prevent Ro-50 from just going well beyond visual range after her ammunition spent. I also expect the batteries of Ro-50 were also heavily worn by July 1945, and diesel fuel was in short supply, therefore submarine captain would be extremely reluctant to move underwater, preferring wait until night, surface and go under diesel.

 

[Cockroach]

So, in effect? Handwave, blatant handwave, arbitrary incompetence, yet more blatant handwaves, instant nuclear physics and weapons design expertise outta nowhere...

 

[marathag]

Finally, while Indianapolis carried uranium for Little Boy it takes rather more than just a critical mass of Uranium to get a proper boom

Those 9 rings were around 84 pounds of HEU, you need approx. 33 pounds for critical mass if implosion is used.
But Rings are the wrong geometry, and a gun design won't clue you to implosion.

Another problem was the overall enrichment level.
I believe the 9 large rings were 80%, while the smaller 6 rings was 94%

Little Boy was only 1.4% efficient. less than 2 pounds of the U-235 actually fissioned

Gun designs are horribly inefficient use of HEU for a bomb, but are relatively 'easy'

 

[Cockroach]

Those 9 rings were around 84 pounds of HEU, you need approx. 33 pounds for critical mass if implosion is used.
But Rings are the wrong geometry, and a gun design won't clue you to implosion.

I wasn't talking in term of mass when I said 'rather more' was needed... I was talking in terms of expertise and weapons design.

 

[Oldbill]

You cannot successfully tow a ship the size of the Indianapolis with a ship that size. The keiaki is a Matsu class DE, of 1620 tons. The Indianapolis is a Portland Class CA, at 10,258 tons. It wont work, you have neither the HP nor the hull shape for this. Add in whatever the substantial weight of tonnage in seawater the Indianapolis has had to have taken on, and the hull damage, it isn't going to happen.