Perhaps the BEST B1G Forum anywhere, here at College Football Fan Site, CFB51!!!

Would a botched D Day also have forced a change of government at Whitehall? Churchill kept hanging on, even at the helm of a wartime government. Anything going sour on the landing could have pushed him out. 

Grandpa GR went ashore in Normandy later in the afternoon. He was an artilleryman, was awarded two Bronze Stars for bravery, and came back as deaf as a post in one ear. Unfortunately, he never told any of this to anyone prior to his sudden death in 2001. We only learned about it by reading his DD214. He passed before the movement to record the vet's stories really reached critical mass. We're taking some of our wedding flowers out to his headstone at Fort Snelling later this morning. 

Churchill was an infantry combat veteran of WWI.  He resigned as First Lord of the Admiralty after his Galipoli brainchild turned into a disaster, and joined the army.

He feared the slaughter of the young men of Great Britain.  And he could't get the disaster of the Dieppe Raid out of his head.  He just didn't want his young men to have to attack the Germans head-on.
That's why Montgomery's plan for Operation Market-Garden was so appealing to him.

Churchill's Galipoli catastrophe is not well known in the US, but if you ever travel to New Zealand, they remember it quite well.  A LOT of the troops killed in that mess were ANZAC's (Austrailians and New Zealanders). 

@Cincydawg quoted the mission history of the Nagasaki bombing above but I have long suspected that it is not accurate.  If you read closely, you will note that the bomb was WAY off target and if you read more about the mission you will learn that Bockscar was running low on fuel and could not have made it back to even Okinawa if they had lingered much longer, especially with the heavy Fat Man Bomb still on board.  Worse, it would have been extremely unsafe to attempt landing with the bomb on board and AFAIK they didn't have explicit permission to drop the thing over the ocean in the event of this problem. 

Consequently, I have long suspected that the Bockscar crew (or just the bombardier) simply dropped it by radar without visual confirmation and that is why it ended up about 2mi away from the intended aiming point.  My theory is that either:
A)  The crew simply decided to ignore the order to get visual confirmation, dropped the bomb by radar, and agreed among themselves not to ever tell anyone, or
B)  The bombardier got increasingly optimistic as fuel got increasingly scarce and simply thought he saw the aiming point even though he actually didn't. 

Note that the Nagasaki bomb was considerably more powerful (21kt vs 16kt) and yet did less damage and killed less people because they botched the aim. 

Side note:
I visited the Trinity site a few years ago (it is open to the public two days a year so check and plan ahead if you want to go).  The Hiroshima bomb was, as someone above noted, untested.  That was because it was a simpler design. 

I'm not a physicist so I don't know this stuff very well but my limited understanding is roughly this:
In order to achieve a nuclear detonation you need to compress fissile material.  The Hiroshima Bomb was a "gun type" bomb.  It achieved this compression by essentially shooting a uranium bullet into a Uranium mass.  This was fairly simple (to the geniuses that designed the bombs) so they didn't feel a need to test it.  The Nagasaki Bomb was an implosion bomb.  It was cylindrical and there were a bunch of conventional shaped charges surrounding the fissile core.  Blowing up the shaped charges created the compression.  They tested it first because if anything went wrong with the charges (ie, if they were not spaced correctly) the fissile material would simply blow out one side instead of detonating. 

The decision not to test the gun type bomb was risky and that is why they did test the other one.  If the bomb had failed to detonate the Japanese would have found it and known exactly what we were up to.  Worse, they would have acquired our fissile material. 

Your description of the two warhead types is accurate.  The challenge with the implosion technique is to ensure all the charges fire at the same time, as you imply.  The design also was based on plutonium, which is used in the most efficient devices today (not uranium).  Plutonium is an artificial element that was generated in the reactors at Hanford, Oregon, and one reason that area is rather polluted.

The US had enough fissile material for a third bomb, but a fourth would be delayed while more was generated.  The U-235 in the first type was separated from U-238 at Oak Ridge using long tubes that separated gases by weight, they used UF6 which is highly corrosive but gaseous.  The first trickle out would be enriched in U-235.  (gaseous diffusion process).  The B-29 Bockscar is at the AF Museum in Dayton, OH (which is an incredible museum).

The book Enola Gay is quite excellent in my view.

Anyway, I'm pondering the Allied advance through the bocage if the only beachead was Utah.  The British around Caen soaked up the German armor because it was open country, the bocage would been mostly infantry and antitank battles and artillery, not armor, I think.  The Germans might have been able to move a 2-3 panzer divisions to the East, or they could have held them in reserve against any allied breakout.  As it was, the German 7th Army got chewed up in the Falaise Pocket.

My guess here, and CWS can chime in since we're guessing, is that the Allies might have needed another 2 months to break out.

Another item mentioned by someone is operation Anvil, the invasion that followed in southern France.  That likely would have occurred and faced little resistance unless you think the Germans could have reoriented some troops in that direction.  Those troops basically had a route march hampered only by supply limitations.  So, if the D-Day invasion is somehow hemmed up, the Med invasion would cause the Germans great difficulty as they tried to reorient, and the new foes would be coming up through what starts to be good tank country.

That was a good point whoever posted it.