At 3:49 in the morning, Major Charles W. Sweeney taxied to the main runway at Tinian Airbase. After receiving his clearance for take off, he increased the throttle to the four Wright Duplex-Cyclone superturbocharged radial engines that provided the 8,800 horsepower required to get the Superfortress off the ground. He was carrying Fat Man, which was the bomb that actually ended the war.
The plane made a rendezvous with other planes over Yakushima Island. After receiving information from the weather planes, it then proceeded to Nagasaki at an altitude of 30,000 feet. The plane had to fly slower than normal in an effort to conserve fuel because of a faulty fuel pump. Because of this, Nagasaki started to cloud over. They were about to use the radar to drop the bomb but the clouds cleared over the target.
At 10:58AM Nagasaki time, the bomb bay of Bock's Car was opened and Fat Man was released. It would detonate 43 seconds later at an altitude of 1,650 feet. The bomb had an approximate yield of approximately 21,000 tons of TNT and it was about 1.5 miles off its target. Because of this, the blast was confined to the Urakami Valley and as a result much of the city was protected by the intervening hills.
It is estimated that 35,000 people were killed in the bomb blast and another 60,000 were wounded. Because of the error in the drop, the bomb hit over the city's industrial area. I'm not sure how many people were later affected by the radioactive effects of the bomb. This bomb was roughly 1/100th the payload of the current Peacekeeper missile.
Because of the delays in the mission and the faulty fuel pump, Bock's Car did not have enough fuel to make it to Iwo Jima. Instead, it was decided they would land at Okinawa. Upon arriving there, Sweeney circled the field for 20 minutes while he waited for clearance to land. After still not receiving clearance, he decided to land anyway.
Because they only had enough fuel for one landing attempt, Sweeney brought Bock's Car in hot. Since they touched the runway hard, they swerved immediately and almost hit some parked planes. They were able to regain control and didn't have enough braking power to not run off the runway, so they did a 90 degree turn and then stopped. The flight engineer estimated they had 5 minutes worth of fuel remaining.
Bock's Car was returned to the United States in November 1945. It served with the 509th Bombardment Group in Roswell, NM until August of 1946 when it was transferred to Davis-Monthan for storage. It would be flown to its current home in 1961.
It was replaced with what is known as the Mother of All Bombs, making this the Grandmother of all Bombs (I guess).