Defensive use of atomic bombs by Dai-Nippon Teikoku Rikugun.

[OpanaPointer]

This is hopefully going to remain about what plans, if any, the Army had for atomic bombs if they had been developed before Downfall execution had begun. Any help would be appreciated.

My own thoughts on this would be that the bomb or bombs would have been used at mines, ready to close an avenue of attack, or to obliterate a landing zone, or, wildly, to close the Kanmon Railway Tunnel.

[wm]

not over the invasion fleet?

[Carl Schwamberger]

One common proposal in the speculations is for a submarine to carry the bomb into a US port & detonate.

[OpanaPointer]

not over the invasion fleet?

As I understand it they wouldn't have had a bomb small enough to be taken into the air. Also, routine dispersal of ships would reduce the "bag" from such a bomb.

[OpanaPointer]

One common proposal in the speculations is for a submarine to carry the bomb into a US port & detonate.

And that would be an offensive action. I could see a freighter sneaking into Pearl.

[Carl Schwamberger]

One common proposal in the speculations is for a submarine to carry the bomb into a US port & detonate.

And that would be an offensive action. I could see a freighter sneaking into Pearl.

Traffic in & out of PH was that poorly controlled in 1945?

A defensive deployment by submarine would be off a beach with heavy logistic traffic. While dispersal waives away catastrophic damage to a fleet, it would disrupt operations.

[OpanaPointer]

One common proposal in the speculations is for a submarine to carry the bomb into a US port & detonate.

And that would be an offensive action. I could see a freighter sneaking into Pearl.

Traffic in & out of PH was that poorly controlled in 1945?

I'd have to ask Com14th.

A defensive deployment by submarine would be off a beach with heavy logistic traffic. While dispersal waives away catastrophic damage to a fleet, it would disrupt operations.

I have low confidence that a nuke would kill enough ships to make it worthwhile as a anti-shipping device. How many ships did Test Baker actually sink? Anybody?

[wm]

I suppose nine. Its base surge contaminated "beyond repair" many others.

[OpanaPointer]

Thanks. We have to allow that the RN and USN wouldn't be that closely packed and many of the ships would be steaming on "race track" courses so they could cut and run if the chrysanthemums started to blossom. I suggest five ships sunk and a like number contaminated by seawater returning to the sea. Only the sunk ones would be immediately out of action. The contaminated ones would need time for the decimation of the crews to render them unable to perform their roles.

IIRC the targets for the air and sea suicide forces would be troop ships. SWAG two thousand troops on each ship. Immediate losses ~ten thousand troops less those (temporarily) saved by other ships. None of them combatants. Poor return for one of the few atomic bombs Jap might have had that cool October day.

Land targets?

[wm]

Let's try half-way between the first wave of landing troops (already on the beach) and the second wave of approaching landing crafts. Delivered by a fast armored boat (good against let's say up to 20mm rounds.)

I suppose the base surge will kill everybody in the two-kilometer radius.

[OpanaPointer]

Tom Lewis speculates that a first off Japanese a-bomb would be about the size of a pick-up truck and much heavier. I don't know the best boats for moving that sucker expeditiously. If it was the only boat approaching the landing force staging area it would have probably received a crumpet and a cuppa from the ships in that area. I can picture the skipper pushing the button as soon as concentrated fire starting hitting his boat.

The advantage to using them on the land is that the IJA could pick the locations for the "mines" to be planted. A narrow mountain pass with steep walls sounds good to me. Anybody familiar with Kyushu? Want to front some candidate area?

[wm]

A small boat with a powerful engine, launched from the shore will reach the detonation point in a minute. I don't think they could stop it in such a short time.
And they really built and planned to use such things (full of conventional explosives.)

You can't do much immediate damage with a ground burst, uneven terrain will shelter the troops quite effectively.

[OpanaPointer]

I'm thinking the ships closest to the shore would be on hair trigger, with PTs and DDs zipping in and out. The small IJN/IJA boat is going to be somewhat bewildered by the mass of shipping in front of them.

As for the shoreward applications, I don't know the terrain that well.

[wm]

Let's replace the boat with something in the vein of the ancient HD-4 hydrofoil from 1919.
With four solid-fuel rockets from the Ohka and one tonne of thrust, it will probably need only 20 seconds.
There will be no skipper; such a contraption could be steered remotely. But even that isn't needed. Just point the thing in the general direction and let it fly as the crow flies.

In a narrow mountain pass with steep walls, an airburst can be simulated by placing the bomb high on one of the walls.
But we don't know where the Americans are going to land so we will have to wait till they do it.
But with such a monstrosity in tow, it will be hard without them noticing it.

[Carl Schwamberger]

Thanks. We have to allow that the RN and USN wouldn't be that closely packed and many of the ships would be steaming on "race track" courses so they could cut and run if the chrysanthemums started to blossom. I suggest five ships sunk and a like number contaminated by seawater returning to the sea. Only the sunk ones would be immediately out of action. The contaminated ones would need time for the decimation of the crews to render them unable to perform their roles. ...

I was not much concerned with the number of ships sunk, but the disruption of build up operations. Make the attack at H+4 or +8. The ships are thrown into chaos all the small craft, the LCM ect... are swamped or sunk and crews injured. Whatever EMP effect of radio comm. Ashore the Beach Master unit is neutralized as are any others unfortunate to be on the beach at the moment. So, without sinking a single ship: long term eye & ear damage to everyone on deck for a couple kilometers from surface zero, significant numbers of small craft out of action, a mini Tusami across the beach putting all units there and vehicles/material out of action. Just neutralizing the beach control unit severely constrains build up operations until a new beach control can be organized.

The detonation is the signal for the counter attack force inland to execute its counter attack plan.