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"All we are saying, give peace a chance!"

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Wonderful poetry and a song IMAGINE from John Lennon

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Wonderful poetry and a song IMAGINE from John Lennon

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There were two kind of Atomic Bombs! This is Little Boy!

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There were two kind of Atomic Bombs! This is Little Boy!

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" 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. It was the first nuclear weapon used in warfare. The bomb was dropped by the Boeing B-29 Superfortress piloted by Colonel Paul W. Tibbets, Jr., commander of the 509th Composite Group of the United States Army Air Forces and Captain Robert A. Lewis. It exploded with an energy of approximately 15 kilotons of TNT (63 TJ) and caused widespread death and destruction throughout the city. The Hiroshima bombing was the second man-made nuclear explosion in history, after the Trinity test.

Little Boy was developed by Lieutenant Commander Francis Birch's group at the Manhattan Project's Los Alamos Laboratory during World War II, a reworking of their unsuccessful Thin Man nuclear bomb. Like Thin Man, it was a gun-type fission weapon, but it derived its explosive power from the nuclear fission of uranium-235, whereas Thin Man was based on fission of plutonium-239. Fission 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, although 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. However, by mid-1946, the Hanford Site reactors began suffering badly from the Wigner effect, the dislocation of atoms in a solid caused by neutron radiation, and plutonium became scarce, 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 the Midway-class aircraft carriers. All the Little Boy units were withdrawn from service by the end of January 1951.

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 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.

Assembly details

Inside the weapon, the uranium-235 material was divided into two parts, following the gun principle: the "projectile" and the "target". The projectile was a hollow cylinder with 60% of the total mass (38.5 kg (85 lb)). It consisted of a stack of nine uranium rings, each 6.25-inch (159 mm) in diameter with a 4-inch (100 mm) bore in the center, and a total length of 7 inches (180 mm), pressed together into the front end of a thin-walled projectile 16.25 inches (413 mm) long. Filling in the remainder of the space behind these rings in the projectile was a tungsten carbide disc with a steel back. At ignition, the projectile slug was pushed 42 inches (1,100 mm) along the 72-inch (1,800 mm) long, 6.5-inch (170 mm) smooth-bore gun barrel. The slug "insert" was a 4 inches (100 mm) cylinder, 7 inches (180 mm) in length with a 1 inch (25 mm) axial hole. The slug comprised 40% of the total fissile mass (25.6 kg or 56 lb). The insert was a stack of six washer-like uranium discs somewhat thicker than the projectile rings that were slid over a 1 inch (25 mm) rod. This rod then extended forward through the tungsten carbide tamper plug, impact-absorbing anvil, and nose plug backstop, eventually protruding out of the front of the bomb casing. This entire target assembly was secured at both ends with locknuts.

When the hollow-front projectile reached the target and slid over the target insert, the assembled super-critical mass of uranium would be completely surrounded by a tamper and neutron reflector of tungsten carbide and steel, both materials having a combined mass of 2,300 kg (5,100 lb). Neutron initiators at the base of the projectile were activated by the impact.

Images for kids

As part of Project Alberta, Commander A. Francis Birch (left) assembles the bomb while physicist Norman Ramsey watches. This is one of the rare photos where the inside of the bomb can be seen.

Two Little Boy type bombs with casings open.

Little Boy in the bomb pit on Tinian island, before being loaded into Enola Gay's bomb bay. A section of the bomb bay door is visible on the top right.

Enola Gay after Hiroshima mission, entering hardstand. It is in its 6th Bombardment Group livery, with victor number 82 visible on fuselage just forward of the tail fin.

The mushroom cloud over Hiroshima after the dropping of Little Boy

Frame house in 1953 nuclear test, 5 psi overpressure

Hiroshima blast and fire damage, U.S. Strategic Bombing Survey map

One of five casings built for the Little Boy bomb used on Hiroshima on display at the Imperial War Museum in London during 2015

In Spanish: Little Boy para niños

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There were two kind of Atomic Bombs! This is Fat Man!

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There were two kind of Atomic Bombs! This is Fat Man!

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Fat Man is the name of the second atomic bomb ever made from plutonium and the second atomic bomb to be used in nuclear warfare. It was dropped over the Japanese island of Nagasaki on August 9, 1945.

Images for kids

Replica mockup of a Fat Man displayed in the National Museum of the United States Air Force, beside the Bockscar B-29 that dropped the original device - black liquid asphalt sealant was sprayed over the original bomb casing's seams, simulated on the mockup.

Mushroom cloud after Fat Man exploded over Nagasaki on 9 August 1945

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Fat Man is the name of the second atomic bomb ever made from plutonium and the second atomic bomb to be used in nuclear warfare. It was dropped over the Japanese island of Nagasaki on August 9, 1945.

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Sadako Sasaki 12 years old in the garden of the Hospital.

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Sadako Sasaki 12 years old in the garden of the Hospital.

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Learn how to fold a paper crane

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A lovely jubbly song about the bomber plane Enola Gay!

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A lovely jubbly song about the bomber plane Enola Gay!

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Orchestral Manoeuvres In The Dark - Enola Gay (Official Music Video)

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Colossus was the world's first programmable electronic digital computer.

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Colossus was the world's first programmable electronic digital computer. British code breakers used Colossus for cryptanalysis during World War II.

These messages were sent between the German High Command, and army field commanders. Reading these messages helped the Allies to win the war.

Codebreaker Max Newman worked at the Government Code and Cypher School (GC&CS) at Bletchley Park. His problem was how to get a machine that would help turn German coded radio teleprinter messages into ordinary language. A group of Post Office telephone engineers led by Tommy Flowers worked out how to do this. Their design, which was called "Colossus" used many vacuum tubes (valves). The first machine, Mark 1, worked in December 1943 and solved its first problem in February 1944. Colossus Mark 2 was even better. It first worked on 1 June 1944, just before the Normandy Landings on D-Day. Ten Colossus computers were in use at the end of the war.

British codebreakers called the teleprinter messages "Fish". The messages had been coded by an unknown German machine. They called the machine and its coded messages "Tunny". Colossus imitated the machine and read the coded message from a punched tape. It tried various possibilities of how two of the wheels had been set up. When Colossus found likely settings for two wheels, the codebreaker designed further programs for Colossus until likely settings of other wheels were found. Colossus did not perform all of the decoding process. It just found likely settings of the machine. The output from Colossus was then worked on by people who had a very good knowledge of the German language.

After the war the British codebreakers found out that the code machine was the Lorenz SZ42. All the secret Colossus computers were taken to pieces, so that no one would find out about them. The designs were destroyed. For thirty years no one knew who made them. Between the early 1990s and 2007, a working copy of a Colossus computer was built. This can be seen at The National Museum of Computing at Bletchley Park in England.

Purpose and origins

Regular radio transmissions of "Tunny" messages started in June 1941. The British codebreakers saw that it used a five-unit code like a teleprinter system. Their research also showed that the coding was being done by a rotor cipher machine with 12 wheels (rotors). For each new message sent, the wheels had first to be turned to new positions. The start position for the message was chosen by the operator who was sending the message. He told the operator who was receiving the message what the start positions were with 12 letters that were not coded. The total number of possible start positions of the 12 wheels was very large indeed.

The coding machine added together the (the un-coded version of the message) and a stream of characters (letters, numbers, punctuation) called the (a stream of seemingly random characters) that it generated to make the ciphertext (the coded version of the message). The ciphertext, which made no sense, was transmitted by radio. At the receiving end an identical machine removed the keystream to produce the plaintext of the message.

If the German operators always worked correctly, no two messages would have the same start position of the wheels. However, mistakes were made. They helped the British codebreakers. On 30 August 1941 two versions of the same message, which was nearly 4,000 characters long, were sent with the same wheel start positions. This mistake was very useful to the research codebreakers. A codebreaker called John Tiltman was able to get the keystream from these messages.

The codebreakers tried to work out the details of the machine from this information, but at first they failed. They were then joined by a young codebreaker called Bill Tutte who was given the job. After a lot of work he succeeded, and produced a logical description of the unseen machine. This work has been described as "the greatest intellectual achievement of world war II". Tutte worked out that the machine made each keystream character by combining the effects of two sets of five wheels. He used Greek letters to name the wheels. He called one set of five the χ ("chi") wheels, and the other set of five the ψ ("psi") wheels. He worked out that the χ wheels moved on one position for each new character coded. The ψ wheels, however, did not move regularly. They only moved on some of the time. Whether or not the ψ wheels moved on was controlled by two wheels that he called two the μ ("mu") or "motor wheels".

Max Newman was a mathematician and codebreaker at Bletchley Park. He was given the job of working out how a machine could break "Tunny" messages. The machine would do a calculation for many possible start positions of the χ wheels. The start position that gave the largest count from this calculation was likely to be the right one. The first machine was called "Heath Robinson". This did not work very well. It had two punched paper tapes that had to work exactly together. One tape contained the ciphertext in a continuous loop. The second looped tape contained patterns made by the wheels of the coding machine. The tapes would often stretch or break when going at 2000 characters each second. Sometimes the tapes would not line up; then the counts were wrong.

Building Colossus

Tommy Flowers worked at the Post Office Research Station at Dollis Hill in north-west London. He was asked to look at the Heath Robinson machine. He thought it was a weak machine. He designed an electronic machine to do the same job. It would make the patterns of the coding machine by electronics so that only one paper tape was needed. In February 1943 he showed Max Newman this design. The design needed 1,500 thermionic valves (vacuum tubes). Few people thought that so many valves could work without a lot failing. More Heath Robinson machines were ordered. Flowers, however, kept with the idea of an electronic machine. He got support from the person in charge of the Post Office Research Station who was called Gordon Radley. Tommy Flowers and his team started work on Colossus in February 1943.

The tape with the message on it had to be read at speed. Tommy Flowers tested the tape reader up to 9,700 letters/second (53 mph (85 km/h)) before the tape broke. He selected 5,000 characters each second as a good speed for regular work. This meant that the paper tape moved at 40 ft/s (12 m/s) or 27.3 mph (43.9 km/h). The electronic circuits were driven by a signal made from reading the sprocket holes of the punched tape.

The first Colossus worked at Dollis Hill in December 1943. Then they took Colossus apart and moved it to Bletchley Park. It got there on 18 January 1944. Harry Fensom and Don Horwood put it back together. Colossus read its first message on the 5th of February. After the first Colossus (Mark 1) there were nine Mark 2 machines. These each had 2,400 valves. They were easier to use. They could be programmed to work at five times the speed of the Mark 1. A Mark 2 Colossus first worked on 1 June 1944.

At first Colossus was only used to find the starting wheel places used for a message (called wheel setting). Codebreakers worked out how to use the Mark 2 to help find the patterns of the cams on the wheels ( wheel breaking). At the end of the war there were ten Colossus computers working at Bletchley Park. This meant that very many messages were decoded.

Design and use

Colossus used parts that were new back then. It used vacuum tubes, thyratrons and photomultipliers. It read from paper with light. It then did a special thing for every letter; the special thing could be changed. It counted how often this special thing was "true". Machines with many vacuum tubes were known to break a lot. They break most when turning on, so the Colossus machines were only turned off when a part broke.

Colossus was the first of the electronic digital machines that could have a program. It could not change as much as later machines:

it had no program inside itself. A person used plugs, wires and switches to change the program. This is how it was set it up for a new thing to do.

Colossus was not a general-purpose machine. It was made for only one kind of code-breaking: counting and Boolean operations.

It was not a Turing-complete computer, even though Alan Turing was at Bletchley Park. This idea had not yet been thought of, and most of the other early modern computing machines were not Turing-complete (like: the Atanasoff-Berry Computer, the Harvard Mark I electro-mechanical relay machine, the Bell Labs relay machines by George Stibitz and others, or the first plans of Konrad Zuse). It took a long time for computers be used for many uses, instead of just a calculator only for working out one hard problem.

Influence and fate

What the Colossus computers were used for was very secret. The Colossus itself was highly secret even for many years after the War. This is why Colossus could not be included in the history of computing hardware for a long time. Nobody knew how important that Flowers and the other people who helped make it were.

Not many people knew about this secret computer, so it had little direct effect on the new design of later computers; EDVAC was the early design which had the most effect on later computer design.

Once Colossus was made, some people now knew that high-speed electronic (no moving parts like electrical relays) digital computing devices could be made and they did not break too much. Just this knowledge was enough to have a big effect on the designs of early computers in Britain and probably in the US. People who knew about Colossus were important in the early computer field in Britain. In 1972, Herman Goldstine wrote that:

Britain had such vitality (energy or drive) that it could right after the war start so many well-planned and well-done projects in the computer field.

In writing that, Goldstine did not know of Colossus. He did not know what it left to projects of people who knew about it. People such as Alan Turing (with the Pilot ACE and ACE), and Max Newman and I. J. Good (with the Manchester Mark 1 and other early Manchester computers). Brian Randell later wrote that:

the COLOSSUS project was an important source of this vitality (energy or drive), one that has not been well understood or known, as has the importance of its places in the time line of the invention of the digital computer.

Colossus plans and machinery were secret from the when they were made. They stayed so after the War, when Winston Churchill ordered the destruction of most of the Colossus machines into "parts no bigger than a man's hand"; Tommy Flowers himself burned the designs in a fireplace at Dollis Hill. Some parts, changed to look innocent, were taken to Newman's Royal Society Computing Machine Laboratory at Manchester University. The Colossus Mark 1 was taken apart and the parts were sent back to the Post Office. Two Colossus computers, along with two copied Tunny machines, were kept. They were moved to GCHQ's new head office at Eastcote in April 1946. They moved again with GCHQ to Cheltenham between 1952 and 1954. One of the computers, known as Colossus Blue, was taken apart in 1959; the other in 1960. In their later years, the computers were used for training. Before that, there had been attempts to change them (sometimes well) for other purposes. Jack Good was the first to use it after the war, getting NSA to use Colossus to do something for which they were planning to build a special purpose machine. Colossus was also used to perform letter counts on one-time pad tape to test for non-randomness.

At this time the Colossus was still secret, long after any of its technical details were of any importance. This was due to the UK's intelligence agencies use of Enigma-like machines which they got other governments to buy. The agencies then broke the codes using different ways. Had the knowledge of the codebreaking machines been widely known, no one would have accepted these machines; rather, they would have developed their own methods for encryption, methods that the UK services might not have been able to break. The need for such secrets slowly went away as communications moved to digital transmission and all- digital encryption systems became common in the 1960s.

Colonel Winterbotham's book The Ultra Secret came out in 1975. This broke the secrecy around the Colossus. After that, details about the computer began to become public in the late 1970s.

A 500-page technical report on the Tunny cipher and its code breaking - entitled General Report on Tunny - was given by GCHQ to the national Public Record Office in October 2000; the complete technical report is online.

Making it again

A team led by Tony Sale built a working copy of a Colossus Mark 2. The plans and machines had been destroyed, but a surprising amount of other material was not destroyed. It was mostly in engineers' notebooks, much of it in the U.S. The optical tape reader might have been the biggest problem, but Dr. Arnold Lynch, its designer, was able to redesign it from his own first writings. The rebuilt Colossus is on show at The National Museum of Computing, in H Block Bletchley Park in Milton Keynes, Buckinghamshire. This is where the Colossus No. 9 was used in the war.

In November 2007, to mark both the end of the work and the start of fundraising (asking for money) they ran a competition. The money would help The National Museum of Computing with a Cipher Competition where the rebuilt Colossus competed with radio amateurs all around the world. The first to hear and decode three messages enciphered would win. They would be enciphered using the Lorenz SZ42 and transmitted from the radio station in the Heinz Nixdorf MuseumsForum computer museum in Germany. The competition was easily won by radio amateur Joachim Schüth. Schüth had gotten ready for the event. He made his own signal processing and code-breaking program using Ada. The Colossus team lost because they wanted to use World War II radios,. They were a day late because of bad radio conditions. The winner's 1.4 GHz laptop, running his own program, took less than a minute to find the settings for all 12 wheels. The German codebreaker said: "My laptop worked on ciphertext at a speed of 1.2 million letters per second-240x faster than Colossus. If you compare the two computers, you could say Colossus had a speed of 5.8 MHz. That is very fast for a computer built in 1944."

Related pages

Jack Copeland, Colossus: Its Origins and Originators (IEEE Annals of the History of Computing, 26(4), October-December 2004, pp. 38-45).

Jack Copeland, Colossus and the Dawning of the Computer Age, in Action This Day, 2001, ISBN: 0-593-04982-9.

That version is a facsimile copy, but there is a transcript of much of this document in '.pdf' format at: , and a web transcript of Part 1 at:

I. J. Good, Early Work on Computers at Bletchley (IEEE Annals of the History of Computing, Vol. 1 (No. 1), 1979, pp. 38-48)

I. J. Good, Pioneering Work on Computers at Bletchley (in Nicholas Metropolis, J. Howlett, Gian-Carlo Rota, (editors), A History of Computing in the Twentieth Century, Academic Press, New York, 1980)

T. H. Flowers, The Design of Colossus (Annals of the History of Computing, Vol. 5 (No. 3), 1983, pp. 239-252)

D C Horwood, A technical description of COLOSSUS I, August 1973, PRO HW 25/24.

Brian Randell, Colossus: Godfather of the Computer, 1977 (reprinted in The Origins of Digital Computers: Selected Papers, Springer-Verlag, New York, 1982)

Brian Randell, The COLOSSUS (in A History of Computing in the Twentieth Century)

Albert W. Small, The Special Fish Report (December, 1944) describe the operation of Colossus to break Tunny messages

Harvey G. Cragon, From Fish to Colossus: How the German Lorenz Cipher was Broken at Bletchley Park (Cragon Books, Dallas, 2003; ISBN: 0-9743045-0-6) - A detailed description of the cryptanalysis of Tunny, and some details of Colossus (contains some minor errors)

Ted Enever, Britain's Best Kept Secret: Ultra's Base at Bletchley Park (Sutton Publishing, Gloucestershire, 1999; ISBN: 0-7509-2355-5) - A guided tour of the history and geography of the Park, written by one of the founder members of the Bletchley Park Trust

Tony Sale, The Colossus Computer 1943-1996: How It Helped to Break the German Lorenz Cipher in WWII (M.&M. Baldwin, Kidderminster, 2004; ISBN: 0-947712-36-4) - A slender (20 page) booklet, containing the same material as Tony Sale's website (see below)

Michael Smith, Station X, 1998. ISBN: 0-330-41929-3.

Jack Copeland: Colossus. The Secrets of Bletchley Park's Codebreaking Computers. Oxford University Press 2006. ISBN: 0-19-284055-X

R. Rojas, U. Hashagen (eds.): The First Computers: History and Architectures. MIT Press 2000. ISBN: 0-262-18197-5. - Comparison of the first computers, with a chapter about Colossus and its reconstruction by Tony Sale.

Images for kids

Cams on wheels 9 and 10 showing their raised (active) and lowered (inactive) positions. An active cam reversed the value of a bit (0→1 and 1→0).

Stepping switch allegedly from an original Colossus presented by the Director of GCHQ to the Director of the NSA to mark the 40th anniversary of the UKUSA Agreement in 1986

Colossus selection panel showing selections amongst others, of the far tape on the bedstead, and for input to the algorithm: Δ Z, Δ\chi and Δ\psi.

Colossus K2 switch panel showing switches for specifying the algorithm (on the left) and the counters to be selected (on the right).

Front view of the Colossus rebuild showing, from right to left (1) The "bedstead" containing the message tape in its continuous loop and with a second one loaded. (2) The J-rack containing the Selection Panel and Plug Panel. (3) The K-rack with the large "Q" switch panel and sloping patch panel. (4) The double S-rack containing the control panel and, above the image of a postage stamp, five two-line counter displays. (5) The electric typewriter in front of the five sets of four "set total" decade switches in the C-rack.

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Colossus was the world's first programmable electronic digital computer. British code breakers used Colossus for cryptanalysis during World War II. These messages were sent between the German High Command, and army field commanders. Reading these messages helped the Allies to win the war.