Re: Yamato Last Sortie - Atomic Bomb "What-if"

"Scott M. Kozel" <kozelsm@xxxxxxxxxxx> wrote in message
news:db6ttm$336$1@xxxxxxxxxxxxxxxxxxxxxxxxxx
> "Carey Sublette" <careysub@xxxxxxxxxxxxx> wrote:
>>
>> "Scott M. Kozel" <kozelsm@xxxxxxxxxxx> wrote:
>>
>> > For maximum effect, they could set the detonator for 100 feet above the
>> > sea, providing a similar effect to the underwater Baker shot at Bikini
>> > atoll in 1946 --
>> > http://nmhm.washingtondc.museum/assets/images/Able2.jpg
>> >
>> > The fireball would be almost a mile in diameter,
>>
>> No, 250 meters (not 1600).
>>
>> > so the effect of a
>> > burst 100 feet above the sea would be similar to the Baker shot which
>> > was about 150 feet underwater.
>>
>> They would be nothing alike.
>>
>> The difference between being actually underwater, and above water is the
>> difference between night and day. Even a matter of a few meters (right at
>> the water surface) has important consequences (like greatly attenuating
>> hydrostatic shock).
>
> My thought behind the "set the detonator for 100 feet above the sea",
> was because the actual bombs at Hiroshima and Nagasaki had aerial
> detonators, not contact detonators; so the 100 foot setting would be to
> insure detonation close to the surface of the sea.
>
> I suppose that my "what-if" scenario for having the atomic bombs ready
> in early April 1945, and deploying the first couple bombs against "major
> purely military targets", could have easily included a second detonator
> on the bomb that would explode the bomb on contact with the sea or land.

Contact detonators were actually developed for Fat Man and were originally
planned for use as a back-up detonator if the proximity fuxe fialed, but
they were deleted later on.

>> They could however have fuzed it with impact fuzes which would come
>> closer
>> to approximating the Baker effects, but the particularly dramatic effects
>> resulting from the underwater burst would still be much reduced.
>
> A sea-surface contact burst with a nuclear fireball 800 feet in
> diameter, would still displace a tremendous amount of sea water and
> would have a huge hydrostatic effect. The airborne shockwave and the
> underwater shockwave would not be kind to any ships nearby.

Nope. The fireball you normally see in images of atmospheric tests is just
(drum roll here) - hot air. And thin hot air at that. It does not create any
sort of hydrostatic shock wave. The atmospheric shock wave bouncing off the
water surface creates an underwater shock, but a weak one (weaker than the
air blast itself) due to the impedance mismatch.

The hull-crushing hydrostatic shock is generated by the energy coupling
between the bomb and the surrounding water in the first few meters of bomb
expansion. It requires the burst point to be at least at the water surface
for reasonable efficiency, but preferably under the surface so that water
surrounds the bomb. The same is true of bunker-busting on land by the way.

>
>> Any air burst would be rather similar to the effects of Able, which were
>> generally underwhelming as far as seriously damaging or sinking ships
>> went.
>
> I agree that the Able shot was underwhelming as far as seriously
> damaging or sinking ships. However, there were major problems with
> respect to the deployment of the bomb --
>
> Test: Able
> Time: 22:00:34 30 June 1946 (GMT)
> 09:00:34 1 July 1946 (local)
> Location: Bikini Atoll lagoon, Marshall Islands
> Test Height and Type: Airburst, Altitude 520 ft (160 m)
> Yield: 23 Kt
>
> History's fourth atomic explosion. A standard Fat Man type Mk 3A
> fission bomb, dropped by B-29 "Dave's Dream", was used in test. The
> bomb fell 980 ft short and 1870 ft left of target, perhaps due to a
> collapsed tail fin. The USS Gilliam was sunk, and four other vessels
> were either sunk or severly damaged. The misplaced bomb resulted in a
> government investigation of the flight crew.
>
> http://www.radiochemistry.org/history/nuke_tests/crossroads/

Yes, I'm quite familiar with this account - since I wrote it myself. My site
is:
http://nuclearweaponarchive.org/Usa/Tests/Crossrd.html

I see that "radiochemistry.org" has no qualms about stealing my web pages
virtually unchanged without credit.

But note that the USS Gilliam was not a battleship, but a transport.

>> > Even if the bomb missed Yamato by 2,000 to 4,000 feet, there would
>> > still
>> > be substantial damage to the ships and considerable loss of life, a
>>
>> Using the low air burst option, a 2000 foot miss would kill crew who were
>> on deck (at least on the side facing the blast), and damage the
>> superstructure substantially (masts, stacks, and other light structures
>> especially). The battleship Nevada was 1800 feet from Able but was not
>> greatly damaged.
>
> That was an airburst at an altitude of 520 ft. No underwater shockwave
> effect there. The Baker shot caused enough damage to the bottom of the
> hull of USS Saratoga, that the ship immediately sank.

I'm not sure what the kill radius of as sea-surface burst would be against a
WW-II battleship.

I'll have to dig into this before I could come up with an estimate.
....

Carey Sublette
--

.

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