Silverplate
Encyclopedia
United States Army Air Forces
The United States Army Air Forces was the military aviation arm of the United States of America during and immediately after World War II, and the direct predecessor of the United States Air Force....
participation in the Manhattan Project
Manhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...
during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
. Originally the name for the aircraft modification project for the B-29 Superfortress
B-29 Superfortress
The B-29 Superfortress is a four-engine propeller-driven heavy bomber designed by Boeing that was flown primarily by the United States Air Forces in late-World War II and through the Korean War. The B-29 was one of the largest aircraft to see service during World War II...
to enable it to drop an atomic weapon
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
, Silverplate eventually came to identify the training and operational aspects of the program as well. The airplane modification project fell under the purview of Project Alberta
Project Alberta
Project Alberta was a section of the Manhattan Project which developed the means of delivering the first atomic bombs, used by the United States Army Air Forces against the Empire of Japan during World War II...
after March 1945. The original directive for the project had as its subject line "Silver Plated Project" but continued usage of the term shortened it to the one word "Silverplate".
Between February 1944 and December 1947 a total of 65 B-29s were modified to Silverplate specifications in five increments. Ultimately 53 of them served with the first nuclear weapons unit, the 509th Composite Group
509th Operations Group
The 509th Operations Group is the flying component of the United States Air Force 509th Bomb Wing , assigned to Whiteman Air Force Base, Missouri. It is equipped with all 20 of the USAF's B-2 Spirit stealth bombers...
.
Initial phase
The project was initiated in October 1943 when Dr. Norman F. RamseyNorman Foster Ramsey, Jr.
Norman Foster Ramsey, Jr. was an American physicist. A physics professor at Harvard University since 1947, Ramsey also held several posts with such government and international agencies as NATO and the United States Atomic Energy Commission...
, a member of the Los Alamos National Laboratory
Los Alamos National Laboratory
Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...
Group E-7, identified the B-29 Superfortress as the only airplane in the U.S. inventory capable of carrying either type of the proposed weapons shapes: the tubular "gun-type fission weapon
Gun-type fission weapon
Gun-type fission weapons are fission-based nuclear weapons whose design assembles their fissile material into a supercritical mass by the use of the "gun" method: shooting one piece of sub-critical material into another...
" shape and the oval plutonium
Plutonium
Plutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
implosion weapon shape. Furthermore, because the attachment box for the main wing spars
Spar (aviation)
In a fixed-wing aircraft, the spar is often the main structural member of the wing, running spanwise at right angles to the fuselage. The spar carries flight loads and the weight of the wings whilst on the ground...
was located between the bomb bay
Bomb bay
The bomb bay or weapons bay on some military aircraft is a compartment to carry bombs, usually in the aircraft's fuselage, with "bomb bay doors" which open at the bottom. The bomb bay doors are opened and the bombs are dropped when over the target or at a specified launching point.Large-sized...
s on the B-29, the gun-type weapon could only be a maximum of in diameter. Prior to the decision to use the B-29 serious consideration had been given to using the British Avro Lancaster
Avro Lancaster
The Avro Lancaster is a British four-engined Second World War heavy bomber made initially by Avro for the Royal Air Force . It first saw active service in 1942, and together with the Handley Page Halifax it was one of the main heavy bombers of the RAF, the RCAF, and squadrons from other...
to deliver the weapon, which would have required much less modification, but the idea was vetoed by General Groves
Leslie Groves
Lieutenant General Leslie Richard Groves, Jr. was a United States Army Corps of Engineers officer who oversaw the construction of the Pentagon and directed the Manhattan Project that developed the atomic bomb during World War II. As the son of a United States Army chaplain, Groves lived at a...
who thought it "beyond comprehension to use a British plane to deliver an American A-bomb".
USAAF sent instructions to its Army Air Forces Materiel Command
Air Force Materiel Command
Air Force Materiel Command is a major command of the United States Air Force. AFMC was created July 1, 1992 through the reorganization of Air Force Logistics Command and Air Force Systems Command....
at Wright Field
Wright Field
Wright Field was an airfield of the United States Army Air Corps and Air Forces near Riverside, Ohio. From 1927 to 1947 it was the research and development center for the Air Corps, and during World War II a flight test center....
, Ohio
Ohio
Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...
, on November 30, 1943, for a highly-classified B-29 modification project. The Manhattan Project would deliver full-sized mockups of the weapons shapes to Wright Field by mid-December, where AAFMC would modify an aircraft and deliver it for use in bomb flight testing at Muroc Army Air Field
Edwards Air Force Base
Edwards Air Force Base is a United States Air Force base located on the border of Kern County, Los Angeles County, and San Bernardino County, California, in the Antelope Valley. It is southwest of the central business district of North Edwards, California and due east of Rosamond.It is named in...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
.
B-29-5-BW 42-6259 (referred to as the "Pullman airplane" from an internal code name assigned it by the Engineering Division of AAF Materiel Command) was delivered to the 468th Bomb Group at Smoky Hill AAB
Salina Municipal Airport
Salina Municipal Airport is a public-use airport located three nautical miles southwest of the central business district of Salina, a city in Saline County, Kansas, United States. It is owned by the Salina Airport Authority....
, Kansas
Kansas
Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...
on November 30, 1943, and flown to Wright Field
Wright-Patterson Air Force Base
Wright-Patterson Air Force Base is a United States Air Force base in Greene and Montgomery counties in the state of Ohio. It includes both Wright and Patterson Fields, which were originally Wilbur Wright Field and Fairfield Aviation General Supply Depot. Patterson Field is located approximately...
, Ohio
Ohio
Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...
, on December 2. Modifications to the bomb bays were extensive and time-consuming. Its four bomb bay doors and the fuselage section between the bays were removed and a single bomb bay configured (the length of the gun-type shape was approximately ). New bomb suspensions and bracing were attached for both shape types, with the gun-type suspension anchored in the aft bomb bay (although its length protruded into the forward bay) and the implosion type mounted in the forward bay. Separate twin-release mechanisms were mounted in each bay, using modified glider tow-cable attach-and-release mechanisms. To document the tests, motion picture camera mounts were installed in the rear bay.
The modifications were made using the dummy bomb shapes as models, and the gun-type shape (code-named Thin Man) proved to be a very close fit. All modifications were made by hand and the process required more than man-hours of labour which could not be completed until February. Engine problems systemic to the B-29 delayed delivery of the Pullman B-29 for flight testing until February 20, 1944.
Testing of bomb shapes
The first test drop at Muroc on March 6 involved a Thin Man, followed on March 14 by two drops of an implosion device shape (codenamed Fat ManFat Man
"Fat Man" is the codename for the atomic bomb that was detonated over Nagasaki, Japan, by the United States on August 9, 1945. It was the second of the only two nuclear weapons to be used in warfare to date , and its detonation caused the third man-made nuclear explosion. The name also refers more...
) fitted with a circular tail fin stabilizer designed by engineers at the National Bureau of Standards. The Thin Man performed without major problems but the Fat Man shapes exhibited significant wobble characteristics, apparently due to poor workmanship and misalignment of the tail fins.
All three bombs had also failed to release immediately, frustrating calibration
Calibration
Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device....
tests. A fourth testing flight resulted in the premature release of a Thin Man shape while the B-29 was still en route to the test range and severely damaged the aircraft. The modified glider mechanisms had apparently caused all four malfunctions, because of the weight of the bombs, and were replaced with British Type G single-point attachments and Type F releases as used on the Lancaster to carry the 12,000 lb Tallboy bomb
Tallboy bomb
The Tallboy or Bomb, Medium Capacity, 12,000 lb, was an earthquake bomb developed by the British aeronautical engineer Barnes Wallis and deployed by the RAF in 1944...
.
After repair of the Pullman B-29 at Wright Field
Wright Field
Wright Field was an airfield of the United States Army Air Corps and Air Forces near Riverside, Ohio. From 1927 to 1947 it was the research and development center for the Air Corps, and during World War II a flight test center....
, testing resumed with three Thin Man and nine Fat Man shapes dropped in the last two weeks of June 1944. Various combinations of stabilizer boxes and fins were tested on the Fat Man shape to eliminate its persistent wobble until an arrangement dubbed a "California Parachute", a cubical tail box with fins angled at 45° to the line of fall, was approved.
The Thin Man gun-type design was based on the fissibility of the very pure isotope produced in microgram quantities by the Berkeley cyclotron. When the Hanford production reactors came on-line in the spring of 1944, the mix of and obtained was found to have a high rate of spontaneus fission. To avoid pre-detonation, the muzzle velocity
Muzzle velocity
Muzzle velocity is the speed a projectile has at the moment it leaves the muzzle of the gun. Muzzle velocities range from approximately to in black powder muskets , to more than in modern rifles with high-performance cartridges such as the .220 Swift and .204 Ruger, all the way to for tank guns...
would need to be greatly raised, making the bomb impractically long. The weapon was re-designed to use . The muzzle velocity required for a fission reaction is much lower, reducing the barrel length of the resulting bomb (now code-named Little Boy
Little Boy
"Little Boy" was the codename of the atomic bomb dropped on Hiroshima on August 6, 1945 by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul Tibbets of the 393rd Bombardment Squadron, Heavy, of the United States Army Air Forces. It was the first atomic bomb to be used as a weapon...
) to less than . This allowed the device to fit into a standard B-29 bomb bay.
The Pullman was modified to its original configuration with the rear bomb bay a standard B-29 design. All subsequent Silverplates were also configured in this manner. The Pullman B-29 was flown to Wendover and assigned to further drop testing in September 1944 with the 216th Base Unit until it was damaged in a landing accident in December.
Wartime production versions
On August 22, 1944, to meet the requirements of the USAAF group about to be formed to train in the atomic mission, a production phase of Silverplate B-29s was ordered under the designation Project 98146-S from the Glenn L. Martin CompanyGlenn L. Martin Company
The Glenn L. Martin Company was an American aircraft and aerospace manufacturing company that was founded by the aviation pioneer Glenn L. Martin. The Martin Company produced many important aircraft for the defense of the United States and its allies, especially during World War II and the Cold War...
's modification center at Omaha, Nebraska
Omaha, Nebraska
Omaha is the largest city in the state of Nebraska, United States, and is the county seat of Douglas County. It is located in the Midwestern United States on the Missouri River, about 20 miles north of the mouth of the Platte River...
. In mid-October the first three of these second increment Silverplate B-29s were delivered to the USAAF and flown to Wendover Army Airfield
Wendover Air Force Base
Wendover Air Force Base is a former United States Air Force base in Utah now known as Wendover Airport. During World War II it was a training base for B-17 and B-24 bomber crews. It was the training site of the 509th Composite Group, the B-29 unit which dropped the Hiroshima and Nagasaki atomic bombs...
, Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
. They were fitted with British single-point bomb releases mounted on a re-designed H-frame suspension rack fitted in the forward bomb bay, so that additional fuel tanks could be carried in the aft bay. A new crew position, called the "weaponeer station", was created in the cockpit with a panel to monitor the release and detonation of the bomb during the actual combat drops. Fourteen production aircraft were assigned to the 393rd Bomb Squadron and three to the 216th Base Unit for bomb drop testing.
By February 1945 the seventeen aircraft of the second increment were themselves in need of upgrades, particularly those of the 216th Base Unit. Four of the planes assigned to the 393rd Bomb Squadron (now a squadron of the 509th Composite Group
509th Operations Group
The 509th Operations Group is the flying component of the United States Air Force 509th Bomb Wing , assigned to Whiteman Air Force Base, Missouri. It is equipped with all 20 of the USAF's B-2 Spirit stealth bombers...
) were immediately transferred to the 216th to meet an increase in its testing tempo. Rather than attempt to modify the existing aircraft a few at a time, a decision was made to start a new production series. The first five of this third increment, known as Project 98228-S, also went to the test unit. The order totalled an additional 28 aircraft, with delivery of 15 designated combat models for the 393rd Bomb Squadron beginning in April; the final 8 were not delivered until after the atomic bomb missions in August.
The final wartime Silverplates incorporated all technical improvements to B-29 aircraft, as well as the final series of Silverplate modifications that included fuel-injected
Fuel injection
Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....
Wright R-3350
Wright R-3350
The Wright R-3350 Duplex-Cyclone was one of the most powerful radial aircraft engines produced in the United States. It was a twin row, supercharged, air-cooled, radial engine with 18 cylinders. Power ranged from 2,200 to over 3,700 hp , depending on the model...
-41 engines, Curtiss Electric reversible-pitch propeller
Propeller
A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid is accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's...
s, and pneumatic actuators for rapid opening and closing of bomb bay doors. Weight reduction was also accomplished by removal of all gun turrets and armor plating. These B-29s represented a significant increase in performance over the standard variants.
Silverplate operational units
Including the Pullman B-29, a total of 65 Silverplate B-29s were produced both during and after World War II. Twenty-nine of these were assigned to the 509th Composite Group during World War II, with 15 used to carry out the atomic bombings of Hiroshima and Nagasaki. An additional twenty-four were assigned to the group for post-war operations as the 509th Bomb Group. Fifty-seven Silverplates were produced by Martin-Omaha and 8 by Boeing-Wichita. Thirty-two were eventually converted to other configurations, 16 were placed in storage and later scrapped, and 12 were lost in accidents (including four of the Tinian bombers). Two, the Enola GayEnola Gay
Enola Gay is a Boeing B-29 Superfortress bomber, named after Enola Gay Tibbets, mother of the pilot, then-Colonel Paul Tibbets. On August 6, 1945, during the final stages of World War II, it became the first aircraft to drop an atomic bomb as a weapon of war...
and Bockscar
Bockscar
Bockscar, sometimes called Bock's Car or Bocks Car, is the name of the United States Army Air Forces B-29 bomber that dropped the "Fat Man" nuclear weapon over Nagasaki on 9 August 1945, the second atomic weapon used against Japan....
, are displayed in museums.
The only other USAF combat unit to use the Silverplate B-29 was the 97th Bomb Wing at Biggs Air Force Base, El Paso, Texas
El Paso, Texas
El Paso, is a city in and the county seat of El Paso County, Texas, United States, and lies in far West Texas. In the 2010 census, the city had a population of 649,121. It is the sixth largest city in Texas and the 19th largest city in the United States...
. In the summer of 1949 it received 27 of the aircraft from the 509th Bomb Wing
509th Bomb Wing
The 509th Bomb Wing is a United States Air Force unit assigned to the Air Force Global Strike Command, Eighth Air Force. It is stationed at Whiteman Air Force Base, Missouri....
when the latter transitioned to B-50D
B-50 Superfortress
The Boeing B-50 Superfortress strategic bomber was a post-World War II revision of the Boeing B-29 Superfortress, fitted with more powerful Pratt & Whitney R-4360 radial engines, stronger structure, a taller fin, and other improvements. It was the last piston-engined bomber designed by Boeing for...
bombers, but within a year all were converted to TB-29 trainers. One other Silverplate B-29, on temporary assignment in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
was converted into a weather reconnaissance aircraft (WB-29) and transferred to the 9th Bomb Wing at Travis Air Force Base
Travis Air Force Base
Travis Air Force Base is a United States Air Force air base under the operational control of the Air Mobility Command , located three miles east of the central business district of Fairfield, in Solano County, California, United States. The base is named for Brigadier General Robert F...
, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
.
Followup program
The U.S. Joint Chiefs of StaffJoint Chiefs of Staff
The Joint Chiefs of Staff is a body of senior uniformed leaders in the United States Department of Defense who advise the Secretary of Defense, the Homeland Security Council, the National Security Council and the President on military matters...
issued a directive in January 1948 for the modification of 225 B-29, B-50, and B-36 bombers to carry nuclear weapons. The project was intended to be completed by December 1948 and was known by the code name "Gem". The modification of 80 B-29s was authorized by Air Materiel Command project DOM-595C, known as Saddletree.
The project included "winterization" of 36 B-29s for operating from Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
bases, and the modification of 36 others to have an air refueling capability under project DOM-599C ("Ruralist"). With the addition of the 80 Saddletree bombers, a total of 145 B-29s were modified to carry nuclear weapons, and 117 of these were assigned to operational units.