The Bockscar, the Fuel Pump That Failed Before Takeoff, and the B-Twenty-Nine at Wright-Patterson That Ended the Second World War

The B-29 that ended the Second World War almost didn’t complete its mission. On August 9, 1945, before the engines ever started, the crew of Bockscar already knew one of their fuel transfer pumps was inoperative. That mechanical failure - combined with weather, a missed rendezvous, and a city shrouded in smoke - would redirect the most powerful weapon ever dropped in combat to a target nobody had woken up expecting.

Bockscar is on permanent public display at the National Museum of the United States Air Force at Wright-Patterson Air Force Base in Dayton, Ohio. Admission is free. The airplane is not a replica.

The Aircraft: What Made the B-29 Revolutionary

The Boeing B-29 Superfortress was unlike anything flying when it entered service in 1944. The wingspan stretches 141 feet - wider than a Boeing 737. The fuselage runs 99 feet. The aircraft could carry 20,000 pounds of bombs to 30,000 feet.

What set it apart from earlier heavy bombers was pressurization. Previous crews flew in unpressurized compartments, wearing oxygen masks and heavy cold-weather gear at altitude and still returning with frostbite. The B-29 gave its crew a shirtsleeve environment. Forward gunners didn’t need oxygen masks during cruise. That was unprecedented.

The engines were Wright R-3350 Cyclone 18-cylinder radials, rated at 3,500 horsepower each, four per aircraft. They had a serious early reputation for overheating and catching fire - the cowling design didn’t cool them adequately, and multiple B-29s went down over the Pacific to engine fires before the Japanese ever fired a shot. Crews flew those airplanes knowing the engines were a liability, monitoring cylinder head temperatures constantly and managing throttles carefully on climb.

Bockscar specifically was a B-29-44-MO variant, built at the Glenn L. Martin plant in Omaha, Nebraska, and delivered to the Army Air Forces in March 1945. Her tail number was 44-27297. The name came from her usual aircraft commander, Captain Frederick Bock - his name, plus “car.” She was assigned to the 393rd Bomb Squadron of the 509th Composite Group.

The 509th: The Most Secret Unit in the Army Air Forces

The 509th Composite Group was stationed at North Field, Tinian, in the Northern Mariana Islands. Almost nobody on the island knew what they were actually doing. They flew specially modified B-29s with redesigned bomb bay doors and weight-reduced equipment. They practiced alone - no formation, no fighter escort, just one airplane flying high and fast, dropping a single large shape and executing a diving escape maneuver.

Three days before the Bockscar mission, on August 6, a B-29 called Enola Gay had dropped the first atomic bomb on Hiroshima. Japan had not surrendered.

The Broken Fuel Pump: A Decision Made in Darkness

At 3:00 AM on August 9, ground crews were swarming around Bockscar at North Field when a technician found that one of the fuel transfer pumps was inoperative. A reserve tank holding 640 gallons of aviation gasoline was effectively stranded - that fuel could not be transferred to the main tanks in flight. It would sit there, unavailable, for the entire mission.

Major Charles Sweeney, the aircraft commander, brought the problem to the mission’s weaponeer, Navy Commander Frederick Ashworth. Together they ran the numbers. The primary target, Kokura Arsenal on the northern shore of Kyushu, was reachable. Okinawa would serve as the emergency recovery field on the return. If weather cooperated and the mission moved quickly, the math worked.

They decided to fly.

The weapon in the bomb bay was a plutonium implosion device the weapons team called Fat Man. It had already been assembled and armed.

Bockscar lifted off from North Field at 3:47 AM.

The Rendezvous That Burned an Hour of Fuel

The mission plan called for a rendezvous over Yakushima Island, off the southern tip of Kyushu, with two escort B-29s. One was the Great Artiste, carrying scientific instruments to measure the blast. The other was a dedicated photo aircraft.

Sweeney arrived over Yakushima on time and began circling. The Great Artiste arrived. The photo aircraft never came.

Sweeney held the rendezvous orbit for 45 minutes, burning fuel he could transfer while the stranded 640 gallons sat untouchable. Every minute in the pattern was irreplaceable range. After 45 minutes, he made the call: they were proceeding to Kokura without the photo ship.

Three Passes Over Kokura

Bombardier Captain Kermit Beahan looked through the Norden bombsight as Bockscar approached Kokura. The atomic mission protocol was absolute: visual confirmation of the target before release. No radar drop was permitted.

Beahan couldn’t see the target. Haze and smoke - some drifting from a conventional firebombing of nearby Yahata the day before - had settled over Kokura Arsenal.

Sweeney took Bockscar around for a second pass. Still obscured. A third pass.

By the third run, Kokura’s flak batteries had tracked this lone B-29 making repeated circuits over a major industrial city. Japanese fighters were climbing through the haze toward them. The fuel state was deteriorating with every orbit.

Three passes. No visual. No drop.

The Turn Toward Nagasaki

Sweeney called Commander Ashworth. The fuel math was brutal. They had enough for one more attempt at another city. The secondary target was Nagasaki, a major port and industrial center on the western coast of Kyushu. If Nagasaki couldn’t be bombed visually, the protocol required jettisoning the weapon over the ocean and recovering at Okinawa.

They turned southwest.

The city of Kokura - today part of the municipality of Kitakyushu - was spared because of weather. The people working at Kokura Arsenal that morning had no way of knowing that the haze over their city was keeping them alive.

The Urakami Valley

Nagasaki sits in a steep valley that traps its own weather. The original aim point, the Mitsubishi Steel and Arms Works at the mouth of the harbor, was obscured by cloud. But to the north, the Urakami Valley showed a break.

Beahan called that he had the target in sight.

At 11:02 AM local time on August 9, 1945, Fat Man separated from Bockscar’s bomb bay. Forty-three seconds later, at approximately 1,800 feet above the Urakami Valley, detonation. Twenty-one kilotons - the equivalent of 21,000 tons of conventional explosive in a single pulse.

The crew had welder’s glass goggles on. They’d trained for the escape maneuver: a sharp diving turn to build airspeed and distance. The shockwave hit Bockscar twice - the direct wave and then the reflection bouncing back off the ground. The airplane bucked both times.

The Return: Flying Home on Empty

Okinawa was closer than Tinian. The navigator worked the fuel numbers. The radio operator tried to raise Okinawa on the emergency frequency and got no response - wrong channels, confusion on the ground side. Bockscar was broadcasting an emergency and nobody was answering.

They finally reached Yontan Airfield, received priority landing clearance, and pointed the nose south.

On final approach, the fuel gauges were reading empty. Not low. Empty.

Sweeney came in fast and steep. He and copilot Lieutenant Charles Donald Albury fired distress flares out the windows to get crash equipment to the runway. The controllers scrambled everything they had.

Bockscar touched down hard, used the full runway, and two engines flamed out on rollout. A third quit before they cleared the pavement.

Four engines in. Three engines out. One broken fuel pump from the beginning.

Where Bockscar Is Today

After the war, Bockscar was flown to Roswell Army Air Field in New Mexico, then to Kirtland Field, then to the boneyard at Davis-Monthan Air Force Base in Arizona, where she sat for several years while the Air Force worked out its museum and preservation priorities.

In 1949, she was selected for permanent preservation. In 1961, she was officially transferred to the Air Force Museum at Wright-Patterson, which has grown into one of the foremost aviation museums in the world - four connected galleries running from the Wright Brothers through the Space Age, free admission.

The restoration work done over the decades reflects her appearance on August 9, 1945, including the markings of the 509th Composite Group. The airframe is original. The same bomb bay. The same blister windows. The same aluminum skin that Sweeney’s crew climbed into at three in the morning on Tinian.

Charles Sweeney: The Only Man Who Flew Both Missions

Major Charles Sweeney was the only person in history to fly on both atomic bomb missions. He flew as aircraft commander of the Great Artiste over Hiroshima on August 6, then commanded Bockscar over Nagasaki on August 9.

He continued in the Air Force after the war, eventually retiring as a Major General. He spent the remainder of his life writing and speaking about those two days. He died in 2004 at the age of 84.

His memoir, War’s End, remains the primary firsthand account of the Nagasaki mission. Additional sourcing for this piece draws from the account by Gordon Thomas and Max Morgan-Witts and from the technical archives maintained by the National Museum of the United States Air Force.

Key Takeaways

• Bockscar launched on August 9, 1945, with a known inoperative fuel transfer pump that left 640 gallons stranded and inaccessible for the entire mission
• A 45-minute rendezvous delay over Yakushima burned irreplaceable fuel before the crew ever turned toward the target
• Three bomb runs over Kokura failed due to smoke and haze; the mission was redirected to Nagasaki as the secondary target
• Fat Man detonated over the Urakami Valley at 11:02 AM with a yield of 21 kilotons - the last atomic weapon ever used in combat
• Bockscar is preserved in flying-era condition at the National Museum of the United States Air Force, Wright-Patterson AFB, Dayton, Ohio - free admission, original airframe