Saturday, December 17, 2016
In 1802, Trevithick built one of his high-pressure steam engines to drive a hammer at the Pen-y-Darren Ironworks in Merthyr Tydfil, Mid Glamorgan . With the assistance of Rees Jones, an employee of the iron works and under the supervision of Samuel Homfray, the proprietor, he mounted the engine on wheels and turned it into a locomotive. In 1803, Trevithick sold the patents for his locomotives to Samuel Homfray.
Homfray was so impressed with Trevithick's locomotive that he made a bet with another ironmaster, Richard Crawshay, for 500 guineas that Trevithick's steam locomotive could haul ten tons of iron along the Merthyr Tydfil Tramroad from Penydarren ( ) to Abercynon ( ), a distance of 9.75 miles (16 km). Amid great interest from the public, on 21 February 1804 it successfully carried 10 tons of iron, 5 wagons and 70 men the full distance in 4 hours and 5 minutes, an average speed of approximately 2.4 mph (3.9 km/h). As well as Homfray, Crawshay and the passengers, other witnesses included Mr. Giddy, a respected patron of Trevithick and an 'engineer from the Government'. The engineer from the government was probably a safety inspector and particularly interested in the boiler's ability to withstand high steam pressures.
The configuration of the Pen-y-darren engine differed from the Coalbrookdale engine. The cylinder was moved to the other end of the boiler so that the firedoor was out of the way of the moving parts. This obviously also involved putting the crankshaft at the chimney end. The locomotive comprised a boiler with a single return flue mounted on a four wheel frame. At one end, a single cylinder with very long stroke was mounted partly in the boiler, and a piston rod crosshead ran out along a slidebar, an arrangement that looked like a giant trombone. As there was only one cylinder, this was coupled to a large flywheel mounted on one side. The rotational inertia of the flywheel would even out the movement that was transmitted to a central cog-wheel that was, in turn connected to the driving wheels. It used a high-pressure cylinder without a condenser, the exhaust steam was sent up the chimney assisting the draught through the fire, increasing efficiency even more.
The bet was won. Despite many people's doubts, it had been shown that, provided that the gradient was sufficiently gentle, it was possible to successfully haul heavy carriages along a "smooth" iron road using the adhesive weight alone of a suitably heavy and powerful steam locomotive. Trevithick's was probably the first to do so; however some of the short cast iron plates of the tramroad broke under the locomotive as they were intended only to support the lighter axle load of horse-drawn wagons and so the tramroad returned to horse power after the initial test run.
Homfray was pleased he won his bet. The engine was placed on blocks and reverted to its original stationary job of driving hammers.
In modern Merthyr Tydfil, behind the monument to Trevithick's locomotive is a stone wall, the sole remainder of the former boundary wall of Homfray's Penydarren House.
A full-scale working reconstruction of the Pen-y-darren locomotive was commissioned in 1981 and delivered to the Welsh Industrial and Maritime Museum in Cardiff; when that closed, it was moved to the National Waterfront Museum in Swansea. Several times a year it is run on a 40m length of rail outside the museum.
Friday, December 9, 2016
The Saturn V consisted of three stages—the S-IC first stage, S-II second stage and the S-IVB third stage—and the instrument unit. All three stages used liquid oxygen (LOX) as an oxidizer. The first stage used RP-1 for fuel, while the second and third stages used liquid hydrogen (LH2). The upper stages also used small solid-fueled ullage motors that helped to separate the stages during the launch, and to ensure that the liquid propellants were in a proper position to be drawn into the pumps.
The S-IVB (sometimes S4b, always pronounced "ess four bee") was built by the Douglas Aircraft Company and served as the third stage on the Saturn V and second stage on the Saturn IB. It had one J-2 engine. For lunar missions it was fired twice: first for the orbit insertion after second stage cutoff, and then for translunar injection (TLI).
The S-IVB evolved from the upper stage of the Saturn I rocket, the S-IV, and was the first stage of the Saturn V to be designed. The S-IV used a cluster of six engines but used the same fuels as the S-IVB — liquid hydrogen and liquid oxygen. It was also originally meant to be the fourth stage of a planned rocket called the C-4, hence the name S-IV.
Eleven companies submitted proposals for being the lead contractor on the stage by the deadline of 29 February 1960. NASA administrator T. Keith Glennan decided on 19 April that Douglas Aircraft Company would be awarded the contract. Convair had come a close second but Glennan did not want to monopolize the liquid hydrogen-fueled rocket market as Convair was already building the Centaur rocket stage.
In the end the Marshall Space Flight Center decided to use the C-5 rocket (later called the Saturn V), which had three stages and would be topped with an uprated S-IV called the S-IVB which instead of using a cluster of engines would have a single J-2 engine. Douglas was awarded the contract for the S-IVB because of the similarities between it and the S-IV. At the same time it was decided to create the C-IB rocket (Saturn IB) that would also use the S-IVB as its second stage and could be used for testing the Apollo spacecraft in Earth orbit.
Douglas built two distinct versions of the S-IVB, the 200 series and the 500 series. The 200 series was used by the Saturn IB and differed from the 500 in the fact that it did not have a flared interstage and had less helium pressurization on board as it would not be restarted. On the 500 series, the interstage needed to flare out to match the larger diameter of the S-IC and S-II stages of the Saturn V. The 200 series also had three solid rockets for separating the S-IVB stage from the S-IB stage during launch. On the 500 series this was reduced to two, and additional linear APS thrusters were added for ullage operations prior to restarting the J-2 engine.
Attitude control was provided by 2 Auxiliary Propulsion System pods, and by engine gimballing. The APS modules provided 150 pounds of thrust each, and were fuelled by a hypergolic mixture of dinitrogen tetroxide and monomethyl hydrazine. They were used for three-axis control during coast phases, roll control during J-2 firings, and (on the 500 series) ullage for the second ignition of the J-2 engine and deorbit into the moon.
A surplus S-IVB tank, serial number 212, was converted into the hull for Skylab, the United States' first space station. Skylab was launched on a Saturn V on May 14, 1973, and re-entered the atmosphere on July 11, 1979. A second S-IVB, serial number 515, was also converted into a backup Skylab, which never flew.
During Apollo 13, Apollo 14, Apollo 15, Apollo 16 and Apollo 17, the S-IVB stages were crashed into the Moon to perform seismic measurements used for characterizing the lunar interior.
Tuesday, December 6, 2016
Many thanks to my readers. I wouldn't have gotten this far without your readership.
Some of you may have noticed that I no longer publish in large amounts as I use d to.
This is because back in those days I was playing catchup, publishing models That I had already built before I started this blog.
Now That I'm all caught up, I only publish one to three models a month.
So no I'm not the speed demon some may have thought.
So on that note, a big hardy thankyoumuchly, and here's to many more years to come of The Great Canadian Model Builder's Web Page!!
Sunday, December 4, 2016
This aircraft served with 46 Squadron, Pilot Lt A.S. Lee, July - August 1917.
The Sopwith Pup was a British single-seater biplane fighter aircraft built by the Sopwith Aviation Company. It entered service with the Royal Flying Corps and the Royal Naval Air Service in the autumn of 1916. With pleasant flying characteristics and good manoeuvrability, the aircraft proved very successful. The Pup was eventually outclassed by newer German fighters, but it was not completely replaced on the Western Front until the end of 1917. Remaining Pups were relegated to Home Defence and training units. The Pup's docile flying characteristics also made it ideal for use in aircraft carrier deck landing and takeoff experiments.
In 1915, Sopwith produced a personal aircraft for the company's test pilot Harry Hawker, a single-seat, tractor biplane powered by a 50 hp Gnome rotary engine. This became known as Hawker's Runabout; another four similar aircraft have been tentatively identified as Sopwith Sparrows. Sopwith next developed a larger fighter that was heavily influenced by this design, though more powerful and controlled laterally with ailerons rather than by wing warping.
The resulting aircraft was a single-bay, single-seat biplane with a fabric-covered, wooden framework and staggered, equal-span wings. The cross-axle type main landing gear was supported by V-struts attached to the lower fuselage longerons. The prototype and most production Pups were powered by the 80 hp (60 kW) Le Rhône 9C rotary engine. Armament was a single 0.303 inch (7.7 mm) Vickers machine gun synchronized with the Sopwith-Kauper synchronizer.
A prototype was completed in February 1916 and sent to Upavon for testing in late March. The Royal Naval Air Service (RNAS) quickly ordered two more prototypes, then placed a production order. Sopwith was heavily engaged in production of the 1½ Strutter, and produced only a small number of Pups for the RNAS. Deliveries commenced in August 1916.
The Royal Flying Corps (RFC) also placed large orders for Pups. The RFC orders were undertaken by sub-contractors Standard Motor Co. and Whitehead Aircraft. Deliveries did not commence until the beginning of 1917. A total of 1,770 Pups were built by Sopwith (96), Standard Motor Co. (850), Whitehead Aircraft (820), and William Beardmore & Co. (30).
In May 1916, the RNAS received its first Pups for operational trials with "A" Naval Squadron. The first Pups reached the Western Front in October 1916 with No. 8 Squadron RNAS, and proved successful, with the squadron's Pups claiming 20 enemy machines destroyed in operations over the Somme battlefield by the end of the year. The first RFC Squadron to re-equip with the Pup was No. 54 Squadron, which arrived in France in December. The Pup quickly proved its superiority over the early Fokker, Halberstadt and Albatros biplanes. After encountering the Pup in combat, Manfred von Richthofen said, "We saw at once that the enemy aeroplane was superior to ours."
The Pup's light weight and generous wing area gave it a good rate of climb. Agility was enhanced by installing ailerons on both wings. The Pup had half the horsepower and armament of the German Albatros D.III, but was much more manoeuvrable, especially over 15,000 ft (4,500 m) due to its low wing loading. Ace James McCudden stated that "When it came to manoeuvring, the Sopwith [Pup] would turn twice to an Albatros' once ... it was a remarkably fine machine for general all-round flying. It was so extremely light and well surfaced that after a little practice one could almost land it on a tennis court." However, the Pup was also longitudinally unstable.
At the peak of its operational deployment, the Pup equipped only four RNAS squadrons (Nos. 3, 4, 8 and 9), and three RFC squadrons (Nos. 54, 46 and 66). By the spring of 1917, the Pup had been outclassed by the newest German fighters. The RNAS replaced their Pups, first with Sopwith Triplanes, and then with Sopwith Camels. The RFC soldiered on with Pups, in spite of increasing casualties, until it was possible to replace them with Camels in December 1917.
The raids on London by Gotha bombers in mid-1917 caused far more damage and casualties than the earlier airship raids. The ineffective response by British interceptor units had serious political repercussions. In response, No. 66 Squadron was withdrawn to Calais for a short period, and No. 46 was transferred for several weeks to Sutton's Farm airfield near London. Two new Pup squadrons were formed specifically for Home Defence duties, No. 112 in July, and No. 61 in August.
The first Pups delivered to Home Defence units utilised the 80 hp Le Rhône, but subsequent Home Defence Pups standardised on the more powerful 100 hp Gnome Monosoupape, which provided improved rate of climb. These aircraft were distinguishable by the addition of vents in the cowling face.
Sopwith Pups were also used in many pioneering carrier experiments. On 2 August 1917, a Pup flown by Sqn Cdr Edwin Dunning became the first aircraft to land aboard a moving ship, HMS Furious. Dunning was killed on his third landing when the Pup fell over the side of the ship. The Pup began operations on the carriers in early 1917; the first aircraft were fitted with skid undercarriages in place of the standard landing gear. Landings utilised a system of deck wires to "trap" the aircraft. Later versions reverted to the normal undercarriage. Pups were used as ship-based fighters on three carriers: HMS Campania, Furious and Manxman. A number of other Pups were deployed to cruisers and battleships where they were launched from platforms attached to gun turrets. A Pup flown from a platform on the cruiser HMS Yarmouth shot down the German Zeppelin L 23 off the Danish coast on 21 August 1917.
The U.S. Navy also employed the Sopwith Pup with famed Australian/British test pilot Edgar Percival testing the use of carrier-borne fighters. In 1926, Percival was catapulted in a Pup off the battleship USS Idaho at Guantanamo Bay, Cuba.
The Pup saw extensive use as a trainer. Student pilots completing basic flight training in the Avro 504k often graduated to the Pup as an intermediate trainer. The Pup was also used in Fighting School units for instruction in combat techniques. Many training Pups were in fact reserved by senior officers and instructors as their personal runabouts while a few survived in France as personal or squadron 'hacks' after the type was withdrawn from combat.
The Pup was officially named the Sopwith Scout. The "Pup" nickname arose because pilots considered it to be the "pup" of the larger two-seat Sopwith 1½ Strutter. The name never had official status as it was felt to be "undignified," but a precedent was set, and all later Sopwith types apart from the Triplane acquired animal names (Camel, Dolphin, Snipe etc.), which ended up with the Sopwith firm being said to have created a "flying zoo" during the First World War
Saturday, November 12, 2016
The Tiger I was a German heavy tank of World War II deployed from 1942 in Africa and Europe usually in independent heavy tank battalions. Its final designation was Panzerkampfwagen VI Tiger Ausf. E often shortened to Tiger. The Tiger I gave the Wehrmacht its first armoured fighting vehicle that mounted the KwK 36 88-mm gun (not to be confused with the 8.8 cm Flak 36). 1,347 were built between August 1942 and August 1944. Production was phased out in favour of the Tiger II.
While the Tiger I has been called an outstanding design for its time, it was over-engineered, using expensive materials and labour-intensive production methods. The Tiger was prone to certain types of track failures and breakdowns, and was limited in range by its high fuel consumption. It was expensive to maintain, but generally mechanically reliable. It was also difficult to transport, and vulnerable to immobilization when mud, ice and snow froze between its overlapping and interleaved Schachtellaufwerk-pattern road wheels, often jamming them solid. This was a problem on the Eastern Front in the muddy rasputitsa season and during extreme periods of cold.
The tank was given its nickname "Tiger" by Ferdinand Porsche, and the Roman numeral was added after the later Tiger II entered production. The initial designation was Panzerkampfwagen VI Ausführung H (‘‘Panzer VI version H’’, abbreviated PzKpfw VI Ausf. H) where 'H' denoted Henschel as the designer/manufacturer. It was classed with ordnance inventory designation SdKfz 182. The tank was later redesignated as PzKpfw VI Ausf. E in March 1943, with ordnance inventory designation SdKfz 181.
Today, only a handful of Tigers survive in museums and exhibitions worldwide. The Bovington Tank Museum's Tiger 131 is currently the only one restored to running order.
Friday, November 4, 2016
"Fat Man" was the codename for the type of atomic bomb that was detonated over the Japanese city of Nagasaki by the United States on 9 August 1945. It was the second of the only two nuclear weapons ever used in warfare, the first being Little Boy, and its detonation marked the third-ever man-made nuclear explosion in history. It was built by scientists and engineers at Los Alamos Laboratory using plutonium from the Hanford Site and dropped from the Boeing B-29 Superfortress Bockscar. For the Fat Man mission, Bockscar was piloted by Major Charles W. Sweeney.
The name Fat Man refers generically to the early design of the bomb, because it had a wide, round shape. It was also known as the Mark III. Fat Man was an implosion-type nuclear weapon with a solid plutonium core. The first of that type to be detonated was the Gadget, in the Trinity nuclear test, less than a month earlier on 16 July at the Alamogordo Bombing and Gunnery Range in New Mexico.
Two more Fat Man bombs were detonated during the Operation Crossroads nuclear tests at Bikini Atoll in 1946. Some 120 Fat Man units were produced between 1947 and 1949, when it was superseded by the Mark 4 nuclear bomb. The Fat Man was retired in 1950.
In 1942, prior to the Army taking over wartime atomic research, Robert Oppenheimer held conferences in Chicago in June and Berkeley, California, in July, at which various engineers and physicists discussed nuclear bomb design issues. A gun-type design was chosen, in which two sub-critical masses would be brought together by firing a "bullet" into a "target". Richard C. Tolman suggested an implosion-type nuclear weapon, but the idea attracted scant consideration.
The feasibility of a plutonium bomb was questioned in 1942. James Conant heard on 14 November from Wallace Akers, the director of the British "Tube Alloys" project, that James Chadwick had "concluded that plutonium might not be a practical fissionable material for weapons because of impurities." Conant consulted Ernest Lawrence and Arthur Compton, who acknowledged that their scientists at Berkeley and Chicago respectively knew about the problem, but could offer no ready solution. Conant informed the director of the Manhattan Project, Brigadier General Leslie R. Groves, Jr., who in turn assembled a special committee consisting of Lawrence, Compton, Oppenheimer, and McMillan to examine the issue. The committee concluded that any problems could be overcome simply by requiring higher purity.
Oppenheimer, reviewing his options in early 1943, gave priority to the gun-type weapon, but as a hedge against the threat of pre-detonation, he created the E-5 Group at the Los Alamos Laboratory under Seth Neddermeyer to investigate implosion. Implosion-type bombs were determined to be significantly more efficient in terms of explosive yield per unit mass of fissile material in the bomb, because compressed fissile materials react more rapidly and therefore more completely. Nonetheless, it was decided that the plutonium gun would receive the bulk of the research effort, since it was the project with the least amount of uncertainty involved. It was assumed that the uranium gun-type bomb could be easily adapted from it.
The gun-type and implosion-type designs were codenamed "Thin Man" and "Fat Man" respectively. These code names were created by Robert Serber, a former student of Oppenheimer's who worked on the Manhattan Project. He chose them based on their design shapes; the Thin Man would be a very long device, and the name came from the Dashiell Hammett detective novel The Thin Man and series of movies by the same name; the Fat Man would be round and fat and was named after Sydney Greenstreet's character in The Maltese Falcon. Little Boy would come last, as a variation of Thin Man.
Neddermeyer discarded Serber and Tolman's initial concept of implosion as assembling a series of pieces in favor of one in which a hollow sphere was imploded by an explosive shell. He was assisted in this work by Hugh Bradner, Charles Critchfield, and John Streib. L. T. E. Thompson was brought in as a consultant, and discussed the problem with Neddermeyer in June 1943. Thompson was skeptical that an implosion could be made sufficiently symmetric. Oppenheimer arranged for Neddermeyer and Edwin McMillan to visit the National Defense Research Committee's Explosives Research Laboratory near the laboratories of the Bureau of Mines in Bruceton, Pennsylvania (a Pittsburgh suburb), where they spoke to George Kistiakowsky and his team. But Neddermeyer's efforts in July and August at imploding tubes to produce cylinders tended to produce objects that resembled rocks. Neddermeyer was the only person who believed that implosion was practical, and only his enthusiasm kept the project alive.
Oppenheimer brought John von Neumann to Los Alamos in September 1943 to take a fresh look at implosion. After reviewing Neddermeyer's studies, and discussing the matter with Edward Teller, von Neumann suggested the use of high explosives in shaped charges to implode a sphere, which he showed could not only result in a faster assembly of fissile material than was possible with the gun method, but which could greatly reduce the amount of material required, because of the resulting higher density. The idea that, under such pressures, the plutonium metal itself would be compressed came from Teller, whose knowledge of how dense metals behaved under heavy pressure was influenced by his pre-war theoretical studies of the Earth's core with George Gamow. The prospect of more-efficient nuclear weapons impressed Oppenheimer, Teller, and Hans Bethe, but they decided that an expert on explosives would be required. Kistiakowsky's name was immediately suggested, and Kistiakowsky was brought into the project as a consultant in October 1943.
The implosion project remained a backup until April 1944, when experiments by Emilio G. Segrè and his P-5 Group at Los Alamos on the newly reactor-produced plutonium from the X-10 Graphite Reactor at Oak Ridge and the B Reactor at the Hanford site showed that it contained impurities in the form of the isotope plutonium-240. This has a far higher spontaneous fission rate and radioactivity than plutonium-239. The cyclotron-produced isotopes, on which the original measurements had been made, held much lower traces of plutonium-240. Its inclusion in reactor-bred plutonium appeared unavoidable. This meant that the spontaneous fission rate of the reactor plutonium was so high that it would be highly likely that it would predetonate and blow itself apart during the initial formation of a critical mass. The distance required to accelerate the plutonium to speeds where predetonation would be less likely would need a gun barrel too long for any existing or planned bomber. The only way to use plutonium in a workable bomb was therefore implosion.
The task of the metallurgists was to determine how to cast plutonium into a sphere. The difficulties became apparent when attempts to measure the density of plutonium gave inconsistent results. At first contamination was believed to be the cause, but it was soon determined that there were multiple allotropes of plutonium. The brittle α phase that exists at room temperature changes to the plastic β phase at higher temperatures. Attention then shifted to the even more malleable δ phase that normally exists in the 300–450 °C (570–840 °F) range. It was found that this was stable at room temperature when alloyed with aluminum, but aluminum emits neutrons when bombarded with alpha particles, which would exacerbate the pre-ignition problem. The metallurgists then hit upon a plutonium–gallium alloy, which stabilized the δ phase and could be hot pressed into the desired spherical shape. As plutonium was found to corrode readily, the sphere was coated with nickel.
The early Y-1222 model Fat Man was assembled with some 1,500 bolts. This was superseded by the Y-1291 design in December 1944. This redesign work was substantial, and only the Y-1222 tail design was retained. Later versions included the Y-1560, which had 72 detonators; the Y-1561, which had 32; and the Y-1562, which had 132. There were also the Y-1563 and Y-1564, which were practice bombs with no detonators at all. The final wartime Y-1561 design was assembled with just 90 bolts.
Because of its complicated firing mechanism and the need for previously untested synchronization of explosives and precision design, it was thought that a full test of the concept was needed before the scientists and military representatives could be confident it would perform correctly under combat conditions. On 16 July 1945, a Y-1561 model Fat Man, known as the Gadget for security reasons, was detonated in a test explosion at a remote site in New Mexico, known as the "Trinity" test. It gave a yield of about 20 kilotonnes (84 TJ). Some minor changes were made to the design as a result of the Trinity test. Philip Morrison recalled that "There were some changes of importance... The fundamental thing was, of course, very much the same."
Wednesday, November 2, 2016
During my researches I discovered that there were signatures on the original Little Boy bomb. Looking at the photographs it was difficult to make out these signatures. There was however one signature that stood out. That signature appears to be "R. Savior". But I could be wrong.
"Little Boy" was the codename for the type of atomic bomb dropped on the Japanese city of Hiroshima on 6 August 1945 during World War II by the Boeing B-29 Superfortress Enola Gay, piloted by Colonel Paul W. Tibbets, Jr., commander of the 509th Composite Group of the United States Army Air Forces. It was the first atomic bomb to be used in warfare. The Hiroshima bombing was the second artificial nuclear explosion in history, after the Trinity test, and the first uranium-based detonation. It exploded with an energy of approximately 15 kilotons of TNT (63 TJ). The bomb caused significant destruction to the city of Hiroshima.
Little Boy was developed by Lieutenant Commander Francis Birch's group of Captain William S. Parsons's Ordnance (O) Division at the Manhattan Project's Los Alamos Laboratory during World War II. Parsons flew on the Hiroshima mission as weaponeer. The Little Boy was a development of the unsuccessful Thin Man nuclear bomb. Like Thin Man, it was a gun-type fission weapon, but derived its explosive power from the nuclear fission of uranium-235. This was accomplished by shooting a hollow cylinder of enriched uranium (the "bullet") onto a solid cylinder of the same material (the "target") by means of a charge of nitrocellulose propellant powder. It contained 64 kg (141 lb) of enriched uranium, of which less than a kilogram underwent nuclear fission. Its components were fabricated at three different plants so that no one would have a copy of the complete design.
After the war ended, it was not expected that the inefficient Little Boy design would ever again be required, and many plans and diagrams were destroyed, but by mid-1946 the Hanford Site reactors were suffering badly from the Wigner effect, so six Little Boy assemblies were produced at Sandia Base. The Navy Bureau of Ordnance built another 25 Little Boy assemblies in 1947 for use by the Lockheed P2V Neptune nuclear strike aircraft (which could be launched from but not land on the Midway-class aircraft carriers). All the Little Boy units were withdrawn from service by the end of January 1951.
The names for all three atomic bomb design projects during World War II—Fat Man, Thin Man, and Little Boy—were created by Robert Serber, a former student of Los Alamos Laboratory director Robert Oppenheimer who worked on the Manhattan Project. According to Serber, he chose them based on their design shapes. The "Thin Man" was a long device, and its name came from the Dashiell Hammett detective novel and series of movies of the same name. The "Fat Man" was round and fat, and was named after Sydney Greenstreet's "Kasper Gutman" character in The Maltese Falcon. Little Boy came last, and was named after Elisha Cook, Jr.'s character in the same film, as referred to by Humphrey Bogart.
Because uranium-235 was known to be fissionable, it was the first approach to bomb development pursued. As the first design developed (as well as the first deployed for combat), it is sometimes known as the Mark I. The vast majority of the work came in the form of the isotope enrichment of the uranium necessary for the weapon, since uranium-235 makes up only 1 part in 140 of natural uranium. Enrichment was performed at Oak Ridge, Tennessee, where the electromagnetic separation plant, known as Y-12, became fully operational in March 1944. The first shipments of highly enriched uranium were sent to the Los Alamos Laboratory in June 1944.
Most of the uranium necessary for the production of the bomb came from the Shinkolobwe mine and was made available thanks to the foresight of the CEO of the High Katanga Mining Union, Edgar Sengier, who had 1,000 long tons (1,000 t) of uranium ore transported to a New York warehouse in 1939. At least part of the 1,200 long tons (1,200 t) of uranium ore and uranium oxide captured by the Alsos Mission in 1944 and 1945 was used in the bomb.
In July 1944, almost all research at Los Alamos was redirected to the implosion-type plutonium weapon. Overall responsibility for the uranium gun-type weapon was assigned to Captain William S. Parsons's Ordnance (O) Division. All the design, development, and technical work at Los Alamos was consolidated under Lieutenant Commander Francis Birch's group.
In contrast to the plutonium implosion-type nuclear weapon and the plutonium gun-type fission weapon, the uranium gun-type weapon was straightforward if not trivial to design. The concept was pursued so that in case of a failure to develop a plutonium bomb, it would still be possible to use the gun principle. The gun-type design henceforth had to work with enriched uranium only, and this allowed the Thin Man design to be greatly simplified. A high-velocity gun was no longer required, and a simpler weapon could be substituted. The simplified weapon was short enough to fit into a B-29 bomb bay.
The design specifications were completed in February 1945, and contracts were let to build the components. Three different plants were used so that no one would have a copy of the complete design. The gun and breech were made by the Naval Gun Factory in Washington, D.C.; the target case and some other components were by the Naval Ordnance Plant in Center Line, Michigan; and the tail fairing and mounting brackets by the Expert Tool and Die Company in Detroit, Michigan. The bomb, except for the uranium payload, was ready at the beginning of May 1945. The uranium 235 projectile was completed on 15 June, and the target on 24 July. The target and bomb pre-assemblies (partly assembled bombs without the fissile components) left Hunters Point Naval Shipyard, California, on 16 July aboard the heavy cruiser USS Indianapolis, arriving 26 July. The target inserts followed by air on 30 July.
Although all of its components had been tested, no full test of a gun-type nuclear weapon occurred before the Little Boy was dropped over Hiroshima. The only test explosion of a nuclear weapon concept had been of an implosion-type device employing plutonium as its fissile material, and took place on 16 July 1945 at the Trinity nuclear test. There were several reasons for not testing a Little Boy type of device. Primarily, there was little uranium-235 as compared with the relatively large amount of plutonium which, it was expected, could be produced by the Hanford Site reactors. Additionally, the weapon design was simple enough that it was only deemed necessary to do laboratory tests with the gun-type assembly. Unlike the implosion design, which required sophisticated coordination of shaped explosive charges, the gun-type design was considered almost certain to work.
The danger of accidental detonation made safety a concern. Little Boy incorporated basic safety mechanisms, but an accidental detonation could still occur. Tests were conducted to see whether a crash could drive the hollow "bullet" onto the "target" cylinder resulting in a massive release of radiation, or possibly nuclear detonation. These showed that this required an impact of 500 times that of gravity, which made it highly unlikely. There was still concern that a crash and a fire could trigger the explosives. If immersed in water, the uranium halves were subject to a neutron moderator effect. While this would not have caused an explosion, it could have created widespread radioactive contamination. For this reason, pilots were advised to crash on land rather than at sea.
The Little Boy was 120 inches (300 cm) in length, 28 inches (71 cm) in diameter and weighed approximately 9,700 pounds (4,400 kg). The design used the gun method to explosively force a hollow sub-critical mass of uranium-235 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. The bomb contained 64 kg (141 lb) 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 0.6 g (0.021 oz) was transformed into several forms of energy, mostly kinetic energy, but also heat and radiation.
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. The first drop test was conducted with L-1 on 23 July 1945. It was dropped over the sea near Tinian in order to test the radar altimeter by the B-29 later known as Big Stink, piloted by Colonel Paul W. Tibbets, the commander of the 509th Composite Group. Two more drop tests over the sea were made on 24 and 25 July, using the L-2 and L-5 units in order to test all components. Tibbets was the pilot for both missions, but this time the bomber used was the one subsequently known as Jabit. L-6 was used as a dress rehearsal on 29 July. The B-29 Next Objective, piloted by Major Charles W. Sweeney, flew to Iwo Jima, where emergency procedures for loading the bomb onto a standby aircraft were practiced. This rehearsal was repeated on 31 July, but this time L-6 was reloaded onto a different B-29, Enola Gay, piloted by Tibbets, and the bomb was test dropped near Tinian. L-11 was the assembly used for the Hiroshima bomb.
When the war ended, it was not expected that the inefficient Little Boy design would ever again be required, and many plans and diagrams were destroyed. However, by mid-1946 the Hanford Site reactors were suffering badly from the Wigner effect. Faced with the prospect of no more plutonium for new cores and no more polonium for the initiators for the cores that had already been produced, Groves ordered that a number of Little Boys be prepared as an interim measure until a cure could be found. No Little Boy assemblies were available, and no comprehensive set of diagrams of the Little Boy could be found, although there were drawings of the various components, and stocks of spare parts.
The Navy Bureau of Ordnance built 25 Little Boy assemblies in 1947 for use by the nuclear-capable Lockheed P2V Neptune aircraft carrier aircraft (which could be launched from but not land on the Midway-class aircraft carriers). Components were produced by the Naval Ordnance Plants in Pocatello, Idaho, and Louisville, Kentucky. Enough fissionable material was available by 1948 to build ten projectiles and targets, although there were only enough initiators for six. All the Little Boy units were withdrawn from service by the end of January 1951.
The Smithsonian Institution displays a Little Boy; it was complete, except for enriched uranium, until 1986. The Department of Energy took the weapon from the museum to remove its inner components, so the bombs could not be stolen and detonated with fissile material. The government returned the emptied casing to the Smithsonian in 1993. Three other disarmed bombs are on display in the United States; another is at the Imperial War Museum in London.