BOEING B-29A SUPERFORTRESS ‚BOCKSCAR‘

Bockscar, sometimes called Bock’s Car, is the name of the United States Army Air Force (USAAF) B-29 bomber that dropped a Fat Man, a plutonium implosion-type nuclear weapon, over the Japanese city of Nagasaki during World War II in the second – and most recent – nuclear attack in history.
Bockscar, B-29-36-MO 44-27297, Victor number, (unit-assigned identification number) # 7, was built by the Glenn L. Martin Company at its bomber plant in Bellevue, Nebraska and one of 15 Silverplate B-29, a Block 35 aircraft, after modification re-designated “Block 36”. It was delivered to the United States Army Air Forces on 19 March 1945 and in April assigned to the 393rd Bombardment Squadron, 509th Composite Group to Wendover Army Air Field, Utah, and was named after Captain Frederick C. Bock.
Silverplate involved extensive modifications to the B-29 to carry nuclear weapons. The bomb bay doors and the fuselage section between the bomb bays were removed to create a single 33-foot bomb bay. British suspensions and bracing were attached for both shape types, with the gun-type (Little Boy) suspension anchored in the aft bomb bay and the implosion type (Fat Man) mounted in the forward bay. Weight reduction was also accomplished by removal of gun turrets and armor plating. These B-29s also had an improved engine, the Wright R-3350-41. The Silverplate aircraft represented a significant increase in performance over the standard variants.
Captain Frederick C. Bock and crew C-13, flew to Wendover Army Air Field in April. The name chosen for the aircraft, and and the nose art painted on it after the mission, was a pun on the name of the aircraft commander. It left Wendover on 11 June 1945 for Tinian, where it arrived 16 June. It was originally given a circle outline around an arrowhead pointing forward tail marking as used by the 509th Composite Group. Bockscar was used in 13 training and practice missions from Tinian, and three combat missions in which it dropped Pumpkin bombs on industrial targets in Japan, in which Bock’s crew bombed Niihama, Musashimo and Koromo.

 PUMPKIN BOMBS

„Pumpkin bombs“ were conventional aerial bombs developed by scientists of the Manhattan Project and used by the United States Army Air Forces against Japan during WW II. It was a close replication of the „Fat Man“ plutonium bomb with the same ballistic and handling characteristics, but it used non-nuclear conventional high explosives. It was mainly used for testing and training purposes, which included combat missions flown with pumpkin bombs by the 509th Composite Group. The name “pumpkin bomb” was the term used in official documents from the large, fat ellipsoidal shape of the munition casing instead of the more usual cylindrical shape of other bombs, intended to enclose the „Fat Man’s“ spherical “physics package” (the plutonium implosion nuclear weapon core).
„Pumpkin bombs“ were produced in both inert and high-explosive variants. The inert versions were filled with a cement-plaster-sand mixture that was combined with water to 1.67 to 1.68 grams per cubic centimetre, the density of the composition high-explosive versions. The filler of both variants had the same weight (2,900 kg) and weight distribution as the inner spherical “physics package” of the „Fat Man“ plutonium bomb.
A total of 486 live and inert training bombs were eventually delivered, the 509th Composite Group dropped a total of 49 bombs on 14 Japanese targets (Ref. 24).

STRIKE  ORDER # 39

On 8 August 1945, the Strike Order # 39 was given to deliver the second atomic bomb Fat Man the next day on 9 August. This order gives the detailed  time scale of the pre-flight preparations and all aircraft involved in the attack as well as the names of the aircraft‘s commanding officers. This time the combat strike consisted of three aircraft, one alternative plane stationed at Iwo Iima to take over the atomic bomb in case of failures of Bockscar and two weather mission aircraft including the Enola Gay latter flown by Captain George W. Marquardt plus two alternative aircraft . Weather Ships had to start at 0230 ET, while the strike Ships followed one hour later. Victor # 77 was the Bockscar with Major Sweeney at the controlls.. The Bombload simply mentioned „Special“, primary target was Nagasaki.

ATOMIC BOMB “FAT MAN”

“Fat Man” was 3.4 m, in length, 1.5 m in diameter and weighed 9,100 kg. The design was an implosion-type weapon using plutonium. A subcritical sphere of plutonium was placed in the center of a hollow sphere of high explosive. Numerous detonators located on the surface of the sphere were fired simultaneously to produce a powerful inward pressure on the capsule, squeezing it and increasing its density. This resulted in a supercritical condition and a nuclear explosion.
The bomb had an explosive force of about 20,000 tons of TNT, about the same as the bomb dropped on Hiroshima. Because of Nagasaki’s hilly terrain, however, the damage was somewhat less extensive than of the relatively flat Hiroshima
Three Fat Man high explosive pre-assemblies designated F31, F32, and F33 were transported to North Field, arriving 2 August.  F33 was expended during the final rehearsal on 8 August, and F31 was the bomb dropped on Nagasaki. F32 presumably would have been used for a third attack or its rehearsal.

STRIKE ON NAGASAKI, DATE: AUGUST, 9^th, 1945

On 1 August the aircraft was given the triangle N tail markings of the 444th Bombardment Group as a security measure, and had its Victor number changed to # 77 to avoid misidentification with an actual 444th aircraft. Except for Enola Gay, none of the 509th Composite Group B-29s had yet had names or nose art painted on the noses. All other names were given or painted after the mission.
The mission included three B-29 bombers and their crews: # 77 Bockscar, # 89 The Great Artiste and # 50 The Big Stink. Bockscar was flown on 9 August 1945 by Crew C-15, which usually manned  The Great Artiste; piloted by Major Charles W. Sweeney, commander of the 393rd Bombardment Squadron; and co-piloted by First Lieutenant Charles Donald Albury, C-15’s aircraft commander. The Great Artiste – flown by Captain Frederick C. Bock – was designated as an observation and instrumentation support plane for the second mission, while The Big Stink – flown by group operations officer Major James I. Hopkins Jr. – as a photographic aircraft. The primary target was the city of Kokura, where the Kokura Arsenal was located, and the secondary target was Nagasaki, where two large Mitsubishi armament plants were located.
Bockscar had been flown by Sweeney and crew C-15 in three test drop rehearsals with inert pumpkin bomb assemblies in the eight days leading up to the second mission, including a final rehearsal the day before. The Great Artiste, which was the assigned aircraft of the crew with whom Sweeney usually flew, had been designated in preliminary planning to drop the second bomb, but the aircraft had been fitted with observation instruments for the Hiroshima mission that took place three days earlier. Moving the instrumentation from The Great Artiste to Bockscar would have been a complex and time-consuming process, and when the second atomic bomb mission was moved up from 11 to 9 August because of adverse weather forecasts, the crews of The Great Artiste and Bockscar instead changed aircraft. The result was that the bomb was carried by Bockscar but flown by the crew C-15 of The Great Artiste.
During pre-flight inspection of Bockscar, the flight engineer notified Sweeney that an inoperative fuel transfer pump made it impossible to use 640 US gallons of fuel carried in a reserve tank. This fuel would still have to be carried all the way to Japan and back, consuming still more fuel. Replacing the pump would take hours; moving the Fat Man to another aircraft might take just as long and was dangerous as well, as the bomb was live. Group Commander Colonel Paul Tibbets and Sweeney therefore elected to have Bockscar continue the mission.
Bockscar took off from Tinian’s North Field at 03:49. The mission profile directed the B-29s to fly individually to the rendezvous point, changed because of bad weather from Iwo Jima to Yakushima Island, and at 17,000 feet cruising altitude instead of the customary 9,000 feet , increasing fuel consumption. Bockscar began its climb to the 30,000 feet bombing altitude a half-hour before rendezvous. Before the mission, Tibbets had warned Sweeney to take no more than fifteen minutes at the rendezvous before proceeding to the target. Bockscar reached the rendezvous point and assembled with The Great Artiste, but after circling for some time, The Big Stink failed to appear. As they orbited Yakushima, the weather planes Enola Gay (which had dropped the first atomic bomb on Hiroshima) and Laggin‘ Dragon reported both Kokura and Nagasaki within the accepted parameters for the required visual attack.
Though ordered not to circle longer than fifteen minutes, Sweeney continued to wait for The Big Stink, finally proceeding to the target only at the urging of Commander Frederich Ashworth, the plane’s weaponeer, who was in command of the mission. After exceeding the original departure time limit by a half-hour, Bockscar, accompanied by the instrument airplane,The Great Artiste, arrived over Kokura, thirty minutes away. The delay at the rendezvous had resulted in clouds and drifting smoke from fires started by a major firebombing raid by 224 B-29s on nearby Yahata the previous day covering 70% of the area over Kokura, obscuring the aiming point. Three bomb runs were made over the next 50 minutes, burning fuel and exposing the aircraft repeatedly to the heavy defenses of Yahata, but the bombardier was unable to drop visually. By the time of the third bomb run, Japanese anti-aircraft fire was getting close, and First Lieutenant Jacob Beser, who was monitoring Japanese communications, reported activity on the Japanese fighter direction radio bands.
The increasingly critical fuel shortage resulted in the decision by Sweeney and Ashworth to reduce power to conserve fuel and divert to the secondary target, Nagasaki. The approach to Nagasaki twenty minutes later indicated that the heart of the city’s downtown was also covered by dense cloud. Ashworth decided to bomb Nagasaki using radar, but, according to Bockscar’s bombardier, Captain Kermit Beahan, a small opening in the clouds at the end of the three-minute bomb run permitted him to identify target features. Bockscar visually dropped the Fat Man at 10:58 local time. It exploded 43 seconds later with a blast yield equivalent to 21 kilotons of TNT at an altitude of 1,650 feet, approximately 1.5 miles northwest of the planned aiming point, resulting in the destruction of 44% of the city
The failure to drop the Fat Man at the precise bomb aim point caused the atomic blast to be confined to the Urakami Valley. As a consequence, a major portion of the city was protected by the intervening hills, but even so, the bomb was dropped over the city’s industrial valley midway between the Mitsubishi Steel and Arms Works in the south and the Mitsubishi-Urakami Ordnance Works in the north.
Because of the delays in the mission and the inoperative fuel transfer pump, the B-29 did not have sufficient fuel to reach the emergency landing field at Iwo Jima, so Sweeney flew the aircraft to Okinawa  Arriving there, he circled for 20 minutes trying to contact the control tower for landing clearance, finally concluding that his radio was faulty. Critically low on fuel, Bockscar barely made it to the runway at Yontan Airfield on Okinawa. With only enough fuel for one landing attempt, Sweeney and Albury brought Bockscar in at 150 miles per hour instead of the normal 120 miles per hour  firing distress flares to alert the field of the uncleared landing. The number two engine died from fuel starvation as Bockscar began its final approach. Touching the runway hard, the heavy B-29 slewed left and towards a row of parked Consolidated B-24 Liberator bombers before the pilots managed to regain control. The B-29’s reversible propellers were insufficient to slow the aircraft adequately, and with both pilots standing on the brakes, Bockscar made a swerving 90-degree turn at the end of the runway to avoid running off the runway. A second engine died from fuel exhaustion by the time the plane came to a stop. The flight engineer later measured fuel in the tanks and concluded that less than five minutes total remained (Ref.: 24).

After the Nagasaki Mission the circle R tail marking of the 6th Bombardment Group, 313th Bomb Wing tail marking was changed to that of the 509th Composite Group, circle outline around an arrowhead pointing forward. At last the Nose Art „Bockscar“ was painted backboard side, Victor # 77 remained unchanged,
After the war, Bockscar  returned to the United States in November 1945. In September 1946, it was given to the National Museum  of the United States Air Force at Wright-Patterson Air Force Base, Ohio. The aircraft was flown to the museum on 26 September 1961, and its original markings were restored (nose art was added after the mission). Bockscar  is now on permanent display at the National Museum of the United States Air Force, Dayton, Ohio, next to a replica of the Fat Man atomic bomb.

 
PLANS FOR MORE ATOMIC ATTACKS ON JAPAN

Major General Leslie R. Groves expected to have another “Fat Man” atomic bomb ready for use on 19 August, with three more in September and a further three in October; a second Little Boy bomb (using U-235) would not be available until December 1945. On 10 August, he sent a memorandum  to General of the Army Georg C. Marshall in which he wrote that “the next bomb … should be ready for delivery on the first suitable weather after 17 or 18 August.” Marshall endorsed the memo with the hand-written comment, “It is not to be released over Japan without express authority from the President”, something President Harry S. Truman had requested that day. This modified the previous order that the target cities were to be attacked with atomic bombs “as made ready”. There was already discussion in the War Department about conserving the bombs then in production for Operation Downfall, and Marshall suggested to Secretary of War Henry L. Stimson that the remaining cities on the target list be spared attack with atomic bombs.
Two more Fat Man assemblies were readied, and scheduled to leave Kirtland Field, New Mexico, for Tinian on 11 and 14 August, and Tibbets was ordered by Major General Curtis LeMay to return to Albuquerque, New Mexico, to collect them. At Los Alamos, New Mexico, technicians worked 24 hours straight to cast another plutonium core.  Although cast, it still needed to be pressed and coated, which would take until 16 August. Therefore, it could have been ready for use on 19 August. Unable to reach Marshall, Groves ordered on his own authority on 13 August that the core should not be shipped.
On Marshall’s orders, Major General John E. Hull looked into the tactical use of nuclear weapons for the invasion of the Japanese home islands, even after the dropping of two strategic atomic bombs on Japan (Marshall did not think that the Japanese would capitulate immediately). Colonel Lyle E. Seeman reported that at least seven Fat Man-type plutonium implosion bombs would be available by X-Day, which could be dropped on defending forces. Seeman advised that American troops not enter an area hit by a bomb for “at least 48 hours”; the risk of nuclear fallout was not well understood, and such a short time after detonation would have exposed American troops to substantial radiation.
Ken Nicols, the District Engineer of the Manhattan Engineer District, wrote that at the beginning of August 1945, “planning for the invasion of the main Japanese home islands had reached its final stages, and if the landings actually took place, we might supply about fifteen atomic bombs to support the troops.” An air burst 1,800–2,000 ft  above the ground had been chosen for the (Hiroshima) bomb to achieve maximum blast effects, and to minimize residual radiation on the ground, as it was hoped that American troops would soon occupy the city (Ref.: 24).

COMMENT: The aircraft B-29 Superfortress (Model number B-29-45-MO, Serial number 44-86292, Victor number # 12, (squadron-assigned identification))  – later known as Enola Gay – was built by the Glenn L. Martin Company at its bomber plant in Bellevue, Nebraska. The bomber was one of the first fifteen B-29s built to the “Silverplate” specification— of 65 eventually completed during and after World War II—giving them the primary ability to function as nuclear “weapon delivery” aircraft. These modifications included an extensively modified bomb bay with pneumatic doors and British bomb attachment and release systems, reversible pitch propellers that gave more braking power on landing, improved engines with fuel injection and better cooling, and the removal of protective armor and gun turrets.
The aircraft was personally selected by Colonel Paul W. Tibbets Jr., the commander of the 509th Composite Group, on 9 May 1945, while still on the assembly line. The aircraft was accepted by the United States Army Air Force (USAAF) on 18 May 1945 and assigned to the 393rd Bombardment Squadron, Heavy, 509th Composite Group. The tail marking was a circle outline around an arrowhead pointing forward. The Crew B-9, commanded by Captain Robert A. Lewis, took delivery of the bomber and flew it from Omaha to the 509th base at Wendover Army Air Field, Utah, on 14 June 1945.
Thirteen days later, the aircraft left Wendover for Guam, where it received a bomb-bay modification, and flew to North Field, Tinian, on 6 July. It was initially given the Victor number # 12, but on 1 August, the tail marking of the 509th Composite Group, circle outline around an arrowhead pointing forward, was changed in circle R tail marking of the 6th Bombardment Group, 313th Bomb Wing, as a security measure and had its Victor number changed to # 82 to avoid misidentification with actual 6th Bombardment Group aircraft.
During July, the bomber made eight practice or training flights and flew two missions, on 24 and 26 July, to drop pumpkin bombs on industrial targets at Kobe and Nagoya. Enola Gay was used on 31 July on a rehearsal flight for the actual mission (Ref. 24).

STRIKE ORDER # 35:

On 5 August 1945, the Strike Order 35 was given to deliver the first atomic bomb Little Boy the next day on 6 August. This order not only gives the detailed  time scale of the pre-flight preparations but also the Victor (identifications) number s of all aicraft involved in the attack as well as the names of the aircraft‘s commanding officers. The combat strike consisted of four aircraft with one alternative plane and four weather mission aircraft including one alternative aircraft . Weather Ships had to start at 0200 ET, while the Combat Ships followed one hour later. Victor # 82 was the Enola Gay with Col. Tibbets at the controlls.

ATOMIC BOMB „LITTLE BOY“

Little Boy was 300 cm in length, 71 cm in diameter and weighed approximately 4,400 kg. The design used the gun method to explosively force a hollow sub-critical mass of enriched uranium and a solid target cylinder together into a super-critical mass, initiating a nuclear chain reaction. This was accomplished by shooting one piece of the uranium onto the other by means of four cylindrical silk bags of cordite powder.
The bomb contained 64 kilograms of enriched uranium. Most was enriched to 89% but some was only 50% uranium-235, for an average enrichment of 80%. Less than a kilogram of uranium underwent nuclear fission, and of this mass only 0.7 grams was transformed into several forms of energy, mostly kinetic energy, but also heat and radiation. The bomb had an explosive force of about 20,000 tons of TNT, about the same as the Fat Man bomb dropped on Nagasaki .
The Little Boy pre-assemblies were designated L-1, L-2, L-3, L-4, L-5, L-6, L-7 and L-11. L-1, L-2, L-5 and L-6 were expended in test drops. L-6 was used in the Iwo Jima dress rehearsal on 29 July. This was repeated on 31 July, but this time L-6 was test dropped near Tinian by Enola Gay. Finally, L-11 was the assembly used for the Hiroshima bomb.

STRIKE ON HIROSHIMA, DATE: AUGUST, 6^th, 1945

During preparation for the first atomic mission, Tibbets assumed command of the aircraft and named it after his mother, Enola Gay Tibbets, who, in turn, had been named for the heroine of a novel. In the early morning hours, just prior to the 6 August mission, Tibbets had a young Army Air Forces maintenance man, Private Nelson Miller, paint the name just under the pilot’s window. Except for Enola Gay, none of the 509th Composite Group B-29s had yet had names painted on the noses. All other names were given after the mission.
Hiroshima was the primary target of the first nuclear bombing mission on 6 August, with Kokura and Nagasaki as alternative targets. Enola Gay, piloted by Tibbets, took off from North Field, in the Northern Mariana Islands, about six hours’ flight time from Japan, accompanied by two other B-29s, The Great Artiste, piloted by Major Charles W. Sweeney carrying instrumentation, and a then-nameless aircraft later called Necessary Evil, commanded by Captain George Marquardt, to take photographs
After leaving Tinian, the three aircraft made their way separately to Iwo Jima, where they rendezvoused at 8,010 ft and set course for Japan. The aircraft arrived over the target in clear visibility at 32,333 ft. Navy Captain William S. Parsons of Project Alberta, who was in command of the mission, armed the bomb during the flight to minimize the risks during takeoff. His assistant, Second Lieutenant Morris R. Jeppson, removed the safety devices 30 minutes before reaching the target area.
The release at 08:15 (Hiroshima time) went as planned, and the Little Boy took 53 seconds to fall from the aircraft flying at 31,060 feet to the predetermined detonation height about 1,968 feet above the city. Enola Gay traveled 11.5 mi before it felt the shock waves from the blast. Although buffeted by the shock, neither Enola Gay nor The Great Artiste was damaged.
Enola Gay returned safely to its base on Tinian to great fanfare, touching down at 2:58 pm, after 12 hours 13 minutes. The Great Artiste and Necessary Evil followed at short intervals. Several hundred people, including journalists and photographers, had gathered to watch the planes return. Tibbets was the first to disembark and was presented with the Distinguished Service Cross on the spot (Ref.: 24).

Comment: After the Hiroshima Mission the Enola Gay‘s circle R tail marking of the 6th Bombardment Group, 313th Bomb Wing tail marking was changed to that of the 509th Composite Group, circle outline around an arrowhead pointing forward. The Victor # 82 remained unchanged, Additional First Atomic Bomb Hiroshima – August 6/1945 was painted on starboard side of Enola Gay.
After the war, the Enola Gay returned to the United States, where it was operated from Roswell Army Air Field, New Mexico. In May 1946, it was flown to Kwajalein, Marshall Islands, for the Operation Crossroads nuclear tests in the Pacific, but was not chosen to make the test drop at Bikini Atoll.
Since 2003, the entire restored Boeing B-29 Enola Gay has been on display at National Air and Space Museums’s Steven Udvar-Hazy Center, Chantilly, Fairfax County, Virginia.

Plans for more atomic attacks on Japan

Major General Leslie R. Groves expected to have another Fat Man atomic bomb ready for use on 19 August, with three more in September and a further three in October; a second Little Boy bomb (using U-235) would not be available until December 1945. On 10 August, he sent a memorandum  to General of the Army Georg C. Marshall in which he wrote that “the next bomb … should be ready for delivery on the first suitable weather after 17 or 18 August.” Marshall endorsed the memo with the hand-written comment, “It is not to be released over Japan without express authority from the President”, something President Harry S. Truman had requested that day. This modified the previous order that the target cities were to be attacked with atomic bombs “as made ready”. There was already discussion in the War Department about conserving the bombs then in production for Operation Downfall (proposed Allied plan for the invasion of the Japanese home islands near the end of World War II), and Marshall suggested to Secretary of War Henry L. Stimson that the remaining cities on the target list be spared attack with atomic bombs.
Two more Fat Man assemblies were readied, and scheduled to leave Kirtland Field, New Mexico, for Tinian on 11 and 14 August, and Tibbets was ordered by Major General Curtis LeMay to return to Albuquerque, New Mexico, to collect them. At Los Alamos, New Mexico, technicians worked 24 hours straight to cast another plutonium core.  Although cast, it still needed to be pressed and coated, which would take until 16 August. Therefore, it could have been ready for use on 19 August. Unable to reach Marshall, Groves ordered on his own authority on 13 August that the core should not be shipped.
On Marshall’s orders, Major General John E. Hull looked into the tactical use of nuclear weapons for the invasion of the Japanese home islands, even after the dropping of two strategic atomic bombs on Japan (Marshall did not think that the Japanese would capitulate immediately). Colonel Lyle E. Seeman reported that at least seven Fat Man-type plutonium implosion bombs would be available by X-Day, which could be dropped on defending forces. Seeman advised that American troops not enter an area hit by a bomb for “at least 48 hours”; the risk of nuclear fallout was not well understood, and such a short time after detonation would have exposed American troops to substantial radiation.
Ken Nicols, the District Engineer of the Manhattan Engineer District, wrote that at the beginning of August 1945, “planning for the invasion of the main Japanese home islands had reached its final stages, and if the landings actually took place, we might supply about fifteen atomic bombs to support the troops.” An air burst 1,800–2,000 ft  above the ground had been chosen for the (Hiroshima) bomb to achieve maximum blast effects, and to minimize residual radiation on the ground, as it was hoped that American troops would soon occupy the city (Ref.: 24).