[syhprum (OP)]

$2billion in nineteens forty money was spent but other than teaching the USSR how to make nuclear bombs had little effect on the war.
the decision to separate  u235 by diffusion and electromagnetic  means instead of centrifuges meant that bombs were not available till Japan was defeated .     

[Zer0]

Re: was the Manahan project a faliure

No!

[Bored chemist]

$2billion in nineteens forty money was spent but other than teaching the USSR how to make nuclear bombs had little effect on the war.
the decision to separate  u235 by diffusion and electromagnetic  means instead of centrifuges meant that bombs were not available till Japan was defeated .     

Imagine that the project had started a little later.
Imagine that the war was over, but the bomb wasn't quite ready yet.
Do you think they wouldn't have finished making and testing it?

If you think that they probably would have carried on with it and checked if it worked (maybe saying it's "for next time" or something) then the (very debatable) question of Japan's defeat is irrelevant.
They were building it "to see if they could".
And, on that basis, it was a success.

[alancalverd]

Once the western front was established in Normandy, the overland invasion of Germany was an inevitable progression into territory that had been pretty much bombed and strafed into impotence. It still took a year to complete.

Japan was a very different proposition: it was a long way from the major ground forces building in India and the USA and at the range limit of most bombers, never mind land-based fighters. Its infrastructure had hardly been damaged by a few very costly bombing raids. It still had a functioning defensive navy, and the capability of building enough fighters to reprise the Battle of Britain in the air.

The  planned invasion of Japan involved an estimated 300 - 500,000 fatalities and maybe 10 times as many permanently disabled casualties over 2 -4 years, at a far greater cash cost to the Allied economies.

In terms of bang per buck, no ship, conventional bomber or tank comes within three orders of magnitude to a nuke, never mind the "disposable asset" infantry and unavailable air support you need to actually occupy the territory.

Manhattan was worth every penny to my dad training ground forces in the Far East and The Boss's dad dropping iron bombs on a very resilient enemy dug into the Pacific islands.

[Zer0]

I Always held negative views & emotions on Nuclear Arsenals...

But i Realize now that maybe Nukes would be Our last bet against an Extraterrestrial Attack.

[alancalverd]

Unlikely. I don't think there are any nuclear surface to air weapons,and said attack will by definition come from above. Retaliation will take a minimum of 4 years to reach the enemy planet, assuming that we know where it is. Better to concentrate on early threat detection and terms of surrender, since they will necessarily have the initiative, the technological superiority, and the military intelligence gained over many years of passive observation.

[Petrochemicals]

When has a military ever said, "hold on, let's not bother with that" ? In the Ukraine? In Britain leading up to 1939? It usually ends up with the other side bothering.

The cavity magnitron had a far greater effect on the war than anything else by a considerable distance. If that was also not bothered with what then?

[Bored chemist]

When has a military ever said, "hold on, let's not bother with that" ?

Every time they didn't invade somewhere.

[alancalverd]

The cavity magnetron certainly made airborne radar a lot more compact, but the Nazis had a perfectly serviceable system too. The European theater was quite different from the Pacific, as I outlined in reply #3 above.

[Petrochemicals]

The cavity magnetron certainly made airborne radar a lot more compact, but the Nazis had a perfectly serviceable system too. The European theater was quite different from the Pacific, as I outlined in reply #3 above.

What if the uranium that was stockpiled and withheld from the Germans by an enteprising mining manager in South Africa was sunk en route to the US by the wolf packs that where not destroyed. What if Japanese u boats sunk the indionapolis en route to the Marianas rather on the return leg?

[paul cotter]

"what ifs" are utterly pointless in retrospect. What if the big bang never happened?

[Petrochemicals]

"what ifs" are utterly pointless in retrospect. What if the big bang never happened?

Not really, it's called learning from you mistakes. What if Europe aligned into a common defence collective would that stop invasion by soviet aggression such as Hungary succumbed to.

[alancalverd]

It has been argued that the failure of the Nazi nuclear program was due to the insistence of someone in authority (I forget who) that graphite could not be used as a moderator, so any reactor experiments had to be carried out with heavy water. The only bulk source was the Rjukan hydroelectric plant, sabotaged by a remarkable group of patriots and adventurers.

Now there's a "what if" for you!

[Bored chemist]

The cavity magnetron certainly made airborne radar a lot more compact,

I suspect that radar actually stayed pretty much the same size- "small and light enough to fit in a plane".
But a magnetron gave a much higher frequency signal and, for a given  antenna size, a smaller wavelength means better precision.
It also gave a higher power output and that means better detection- either you can see smaller targets or you can see then further away depending on how you look at it.
Magnetrons just made or radar a lot better than the opposition.
We could, from a plane, spot the Schnorchel of a U-boat and drop bombs on it.

[alancalverd]

Usual source:

The cavity magnetron was a radical improvement introduced by John Randall and Harry Boot at the University of Birmingham, England in 1940.[2] Their first working example produced hundreds of watts at 10 cm wavelength, an unprecedented achievement.[3] Within weeks, engineers at GEC had improved this to well over a kilowatt, and within months 25 kilowatts, over 100 kW by 1941 and pushing towards a megawatt by 1943. The high power pulses were generated from a device the size of a small book and transmitted from an antenna only centimeters long, reducing the size of practical radar systems by orders of magnitude.[4] New radars appeared for night-fighters, anti-submarine aircraft and even the smallest escort ships,[4] and from that point on the Allies of World War II held a lead in radar that their counterparts in Germany and Japan were never able to close. By the end of the war, practically every Allied radar was based on a magnetron.

Not sure about spotting a snorkel with WWII airborne radar, but if the top was consistently above the waves, the hull of the sub would only be a few feet below the surface (almost certainly giving an intermittent radar return) , and there would be a visible snorkel wake and diesel smoke if the vessel was moving.

[Petrochemicals]

It has been argued that the failure of the Nazi nuclear program was due to the insistence of someone in authority (I forget who) that graphite could not be used as a moderator, so any reactor experiments had to be carried out with heavy water. The only bulk source was the Rjukan hydroelectric plant, sabotaged by a remarkable group of patriots and adventurers.

Now there's a "what if" for you!

I personally believe the German scientists did a good bit of subdifuge, the Nazis by the end of the war where under the impression a nuclear weapon was impossible with uranium, most was sent for high density impactors for guns, some was shipped to Japan for the same purpous. They spent a vast fortune developing wacky weapons but gave up on the bomb.

[paul cotter]

A uranium bomb is a simple matter IF one has the requisite quantity of highly enriched u235. A plutonium bomb requires a much smaller quantity of fissile pl239 which can be chemically separated from reactor byproducts, a much simpler process than uranium enrichment. The plutonium bomb requires a much more complicated initiating system.

[Zer0]

I Always held negative views & emotions on Nuclear Arsenals...

But i Realize now that maybe Nukes would be Our last bet against an Extraterrestrial Attack.

My Fault!
I didn't quite present my thought in detail.

Our last bet could be using it upon Us, not the attacking aliens.
To Avoid becoming Slaves or going thru excruciatingly painful experiments or being dissected alive & being severely mutilated.

For e.g.
If I'm atop a hill being chased by a pride of 10 hungry lionesses...
& All i have for defence is an old style revolver with 6 bullets..
No matter how good my aim maybe, i ain't gonna get em all, then perhaps my best bet would be a single shot from point blank range to my head, Game Over!

P.S. - " What If " the Nazis had built the Bomb first, maybe We all would be having conversations in German, or perhaps We might have been long gone.

[alancalverd]

A superior race would not need or want to use us all for experimental dissection.

Good animal husbandry involves the use of selective pesticides and grooming to ensure healthy happy livestock.

All we need to do is identify priests, philosophers and politicians as laboratory specimens, and enjoy life without parasites.

[Zer0]

There might be a Stark difference between a Technologically Superior race & a Moral & Ethically Superior race.

I won't get into nitty gritty awful details of how bad & severe of a form of Slavery could be imagined.

Those who succumb in the initial attack of the Aliens might have a better Fate than those unlucky ones who might survive.

P.S. - Until Faith & Belief exist, Priests would be around.
Until Democracy & Constitution exist, Politicians would thrive.
Until Awe & Wonder exist, Philosophy would survive.