Jonathan Aylen. The International Journal for the History of Engineering & Technology, Volume 85, Issue 1, 2015.
Blue Danube was the first British atomic bomb deployed during the Cold War. There are accounts of the invention of the first atom bombs as part of the Manhattan Project and their subsequent re-invention in the Soviet Union and in Britain but these stories focus on the science and politics of early weapons development in an atmosphere of secrecy and espionage. History is largely silent on the physical technology and practical engineering of the first nuclear weapon in the UK.
The rapid technical development of Britain’s first atomic bomb is examined, focusing on practical issues of procurement, production, assembly, deployment, maintenance and testing. Neglect of the prosaic aspects of atomic weapons is understandable. Atomic bomb design is an unfashionable, even unwelcome, topic. The technology is complicated. It is shrouded in secrecy. Records are fragmented across Government Departments or incomplete. Some archive records have been withheld and some available records have been subsequently withdrawn.
The neglect of technical development of the atom bomb in the UK distorts our view of how technology develops. Accounts of the bomb focus on a polite story of intellectual effort and formal science rather than engineering and practical technology. Interviews with those involved with Blue Danube design, production and deployment show an undocumented technological effort which encompassed a manufacturer of hot water bottles and a tank engine builder. Technicians struggled to perfect the production of items such as airbags, firing circuits and timing fuzes, often unaware of the full scope of the project they were working on.
This paper takes an evolutionary view and argues that Blue Danube was founded on local knowledge and pragmatic solutions which produced a deterrent that was modified as problems emerged. Development work was distributed widely. The weapon system was built on the back streets of northern towns such as Leeds, Barnsley and Mansfield and in southern suburbs such as Ilford, Weybridge and Shoreham as much as the more familiar sites of Woolwich, Aldermaston and Burghfield. Once the weapon came into service, feedback from RAF rehearsals, trial drops and volume manufacturing caused the bomb to be modified.
Those involved were often expert on one aspect of the bomb’s design, but kept in ignorance about other features of the weapon. Designs were given a ‘Top Secret Atomic’ classification. Information was provided on a ‘need to know basis’. As one respondent from Farnborough said, ‘other things were going on like Yellow Sun and Red Beard, but those were in the next office or the next office but one and I can’t tell you anything about them’. Or, as a former RAF officer said ‘You were encouraged not to be curious. You never talked about “top site” matters outside the wire. You never, ever talked about it in the Mess. It was just “verboten”’. Nevertheless, de facto cooperation emerged as key individuals shared knowledge up and down the supply chain, though not always fully aware of the precise significance of the information conveyed.
Development of Blue Danube
Blue Danube was conceived in secrecy and developed in haste. Work began before the go-ahead was given. Operational Requirement OR 1001 was issued in 1946. This initial specification for Blue Danube—the ‘special weapon’, or the ‘Bomb, Aircraft, HE, 10,000lb MC Bomb’ (initially, LC bomb), or ‘the store’, or ‘Small Boy’, or ‘Ten Thousand Pound Elsie’, as it was variously known—set the overall dimensions. The large size, weight and shape of the bomb were crucial as they determined the four designs for the new generation of jet-propelled V-bombers: Sperrin, Valiant, Victor and Vulcan. At the same time, the British Industrial Group of the Atomic Energy Organization began work in February 1946 to produce plutonium for use in bombs.
The formal decision to proceed with a UK atomic bomb was taken at a small cabinet committee GEN 163 on 8 January 1947. The first planning meeting to build the weapon took place in a curtained and stuffy Library at Woolwich Arsenal in June 1947. The first British-made nuclear explosion took place at the ‘Hurricane Trial’ on the Monte Bello islands, off Western Australia on 3 October 1952—a decisive demonstration that the UK’s warhead concept worked. Delivery of the Blue Danube weapon commenced at the Bomber Command Armaments School at RAF Wittering on 7 November 1953. The first operational V-bomber, a Valiant, WP201, was delivered to the RAF on 15 June 1955. The first live drop from a Valiant at 30,000 feet took place at Maralinga on 11 October 1956, three years after the first bomb had been delivered to the RAF. The Air Ministry recognized ‘for political reasons, Blue Danube was introduced into the service at a fairly early development stage, which would normally be regarded as premature’.
Pre-history of UK development
It is an irony of history that production of atomic bombs ceased briefly worldwide after their initial deployment at Hiroshima and Nagasaki and the post-war Bikini Atoll trials. When David Lilienthal became Chairman of the US Atomic Energy Commission in January 1947 he found just one deployable bomb in existence, few skilled personnel able to assemble other parts that were available and no capacity to manufacture more. The knowledge of how to build a bomb had been dispersed and the existing design had many shortcomings.
Despite helping develop the first two atomic bomb designs as part of the Manhattan project and playing a part in the post-war tests at Bikini Atoll in July 1946, the British were cut off from any further American help by the terms of the USA’s McMahon Act which became law in August 1946. The UK Government decided they had to develop their own ‘special weapon’. The aim was to build a version of ‘Fat Man’ used at Nagasaki on the basis of partial knowledge acquired by British scientists working on the war time project.
An organization called Basic High Explosive Research was formed in June 1947 under the leadership of William Penney who had worked at Los Alamos from June 1944, witnessed the Nagasaki explosion and advised the Americans at the Crossroads’ trials at Bikini Atoll. William Penney had the official title Chief Superintendent, Armaments Research. Penney had both the formal knowledge and the tacit know-how to transfer the essentials of bomb production to his new team. Otherwise, members of the UK team involved in the Manhattan project had dispersed to other roles, although Klaus Fuchs, Egon Bretscher and the circuit designer Ernest Titterton worked at Harwell on atomic energy research.
The project name was soon shortened to ‘High Explosives Research’ (HER) and the design team were given headquarters at Fort Halstead, Dunton Green, near Sevenoaks in Kent with production facilities at Woolwich and testing facilities initially at Foulness in Essex and later also at Orfordness in Suffolk. The RAF and the Royal Aircraft Establishment (RAE) were involved almost from the outset. In due course HER moved to a new site of its own at Aldermaston, a former airfield in Berkshire, which became part factory and part R&D laboratory.
As a result of incomplete knowledge, domestic production imperatives and the desire of technologist to modify, the UK bomb emerged as a local design. This fundamental redesign had major benefits:
Compared with the American weapons at the end of 1946 when all collaboration ended, the first British bomb had several advantages: about 20 per cent greater nuclear efficiency; easy change of explosive power; incomparably better ballistic and aiming qualities; rapid assembly; much safer loading; much improved firing circuits and detonators; sealed electronics, permitting release from a high altitude; and better storage characteristics.
Design selection
Blue Danube worked by nuclear fission. In simple terms, a sub-critical mass of plutonium was slammed into another sub-critical mass of plutonium by implosion of a surrounding jacket of high explosive. Reducing the volume of two hemispheres of plutonium so rapidly means the nuclei find plenty of neutrons to fission, but little surface area to escape from. Fission releases huge quantities of energy and subsequent radioactive fall-out.
Two designs of atomic bomb were developed to fruition during the Manhattan Project of World War II. The first design triggered a chain reaction by firing a particle of uranium down a tube inside the bomb into a mass of uranium. This ‘Little Boy’ design was dropped over Hiroshima on 6 August 1945. While the design was straightforward, production of fissile material U235 proved a bottleneck. So much so, that the bomb exploded over Hiroshima had not been tested due to shortage of uranium.
In the second design of atomic bomb, ‘Fat Man’, a chain reaction was triggered by reducing the volume of fissionable material—in this case plutonium—using high explosives to compress the material symmetrically and with great force. This was the design exploded during the Trinity Test north-west of Alamagordo, New Mexico on 16 July 1945 and above Nagasaki on 9 August 1945. Here the technical difficulty lay in the design of the complex implosion mechanism that triggered a critical mass. The US design was aerodynamically poor as its length was constrained by the short bomb bay of the B29 delivery aircraft.
Supply of fissile material helped determine the choice of British design of atomic bomb. Plutonium was largely manufactured in what seems, in retrospect at least, a ‘cheap and cheerful’ way in an air-cooled graphite pile at Windscale in Cumberland. An adjacent chemical separation plant used solvent extraction to separate plutonium from uranium in the irradiated fuel rods. The uranium fuel rods for Windscale were made at Springfields, Salwick, west of Preston in Lancashire using chemical separation and vacuum casting. The hollow spherical tamper inside the high explosive shell of Blue Danube was natural uranium 238, also from Springfields. A tiny amount of polonium 210 known as an ‘urchin’ was needed as an initiator, providing an intense source of alpha particles at the moment of prompt criticality. This polonium was made from irradiated bismuth at Windscale, and later Risley. The scientific team may also have appreciated the ‘Fat Man’ design was less likely to go critical by accident than the ‘Little Boy’ alternative, while plutonium is fairly benign and easy to handle in small finished quantities compared to uranium 235.
Choice of the ‘Fat Man’ design for the UK atomic bomb had two consequences. Firstly, Blue Danube was large. Use of an implosion triggered by conventional high explosives resulted in a weapon weighing some 10,000 lb, just over 24 feet long and almost 62 inches in diameter. The overall bomb weighed 4½ tonnes, but perhaps 2½ tonnes of this were high explosive. Secondly, a key feature of the design was the double layer of explosive lenses that triggered the implosion. So, paradoxically, design and maintenance of high explosives and their accurate detonation were the key focus of an atomic bomb delivery system. Non-destructive testing of the explosive lenses using X-ray techniques became a key maintenance activity.
The Blue Danube design did not replicate the US ‘Fat Man’. The American case was heavily armoured. The British version was a light internally braced ballistic casing. The explosive sphere was redesigned from first principles using a combination of twelve pentagonal and twenty hexagonal shapes to form a sphere—not unlike the outer pattern of a modern soccer ball. The first version of the British bomb was primed in flight through In Flight Loading (IFL) of the core. The UK bomb was designed to work at higher altitudes and lower temperatures than its US equivalent.
Engineering design and the prototype
Penney’s approach to engineering design was the familiar method of breaking down the weapon into its key packages and entrusting design, development and testing of the sub-assemblies to small teams. HER at Fort Halstead set up four working parties to complement their in-house work on the core of the bomb ‘to ensure that all aspects of the project would receive adequate consideration’. These committees were named C, A, F and H which covered Ballistic Case and Supporting Structure (C); Aircraft Installations (A); Fuse (sic) (F) and Handling and Transportation (H). The overall weapon would then be assembled into a prototype from its components. In turn, each team was broken down into smaller groups and allotted specific tasks. This helped maintain secrecy. What appeared to be a highly centralized and directed project was, in truth, widely distributed in terms of delivery across both public bodies and private firms. The project involved a high degree of coordination behind a wall of secrecy.
While this process of deconstruction and reconstruction is a standard approach to engineering, it is not clear that many conventional engineers were involved in the lead team at HER at Fort Halstead. The initial team briefed by Penney—a mathematician—at Woolwich in 1948 was composed of a mix of scientists including chemists and fellow mathematicians. The conceptual and detailed design work for Blue Danube was undertaken within a narrow circle of government departments. This meant scientists were entrusted with production designs. As a result, ‘the design of the weapon is sound enough in principle, but unpolished in the engineering sense, leading inevitably to an expensive and long-drawn-out process of improving the design of many of the component parts’.
The technologies of the Blue Danube bomb
The atom bomb was a set of technologies. It brought together pioneering electronics with novel nuclear materials and conventional, heavyweight explosives. The casing posed aerodynamic problems. Preparation of the fissile material required feats of chemical engineering.
The bomb was built up from six packages of components, each with its own set of development problems and manufacturing challenges. They were the outer ballistic casing; the suspension system for the central physics package (or warhead); the fuzes; the firing mechanism and detonators; the physics package combining a high explosive outer shell and the tamper, core and urchin; and, finally, a new set of organizational routines and facilities surrounding handling, storage and deployment. This omits associated developments which have commanded more public attention, such as a new generation of medium range jet bombers, the difficulties of making fissile material for the core, and the awkward nature of the nuclear testing process.
The ballistic casing and support structure—the role of RAE Farnborough
The outer ballistic casing and internal support structure illustrate the combination of public sector research and private sector manufacture required to build Blue Danube. What appears to be a simple, delegated task actually required considerable experiment, technical development, design work and engineering ingenuity.
The ballistic casing for an atom bomb has four functions. The outer shape of the case determines the bomb’s free-fall characteristics and accuracy. The strength of the case allows the bomb to be suspended in the bomb bay. The internal structure of the centre section holds the physics package in place and maintains gentle pressure on the outer explosive sphere. Finally, the casing encloses the arming mechanism, fuzes, firing mechanisms and batteries necessary to trigger the bomb. The front and rear casings also played a structural role as they were winched up against the fore and aft crutches in the bomb bay. At the front, a fibreglass radome allowed the primitive radar fuzes to operate.
The design, testing and supervision of the development of the overall bomb casing was delegated to the RAE whose central role in design work and managing contracts is underplayed in official accounts. The RAE was to become even more prominent in later weapon developments such as adaption of US hydrogen weapons, conceptual design of Blue Steel and design of WE177.
The RAE was involved in Blue Danube from 1948, not just on casing design and aerodynamics, but also the physical and electrical integration of the bomb into the aircraft. Farnborough had set up a division called ‘ARL’—the ‘Airfield Radio Laboratory’. This innocuous name was retained as work began on Blue Danube under the leadership of Sid Hunwicks. Such misnomers were typical of the dissembling surrounding the weapon. RAE used a secure compound for atomic bomb development work located at the remote southern end of Farnborough airfield. This ARL compound had aircraft access and was occupied around 1950. It was in use by 1952 for bomb loading trials on the Valiant prototype flown in from Vickers at Weybridge. Photographic evidence shows ARL had a staff of at least twenty-two engineers and ten support staff working on Blue Danube in 1953, protected by an armed special police unit.
The RAE was responsible for the design and ballistics of the complete casing and for elements of the implosion sphere such as the support structure and IFL. The casing had a flush riveted stressed skin over an inner airframe. The ballistic shape of the bomb was designed by Dr G. J. Richards. A programme of wind-tunnel testing, trials of rocket-propelled models and tests of 1/3.4 scale models, followed by full-scale trials at Orfordness were used to confirm the shape. Wind-tunnel testing at Farnborough revealed the singular predicament that the bomb was reluctant to leave the aircraft due to flow of air in the bomb bay with local lift at the nose and downward flow at the tail driving the weapon back up into the bomb bay. This would cause considerable embarrassment to the crew if the time-delay fuze kicked in.
Two measures were taken to make sure the bomb did fall away from the aircraft. Blue Danube had four fixed fin stubs which were limited in span by the diagonal size of the bomb bay. Extendable ‘flip out’ fins were fitted to lengthen the span of these stubs or ‘fin gloves’. The flip-out fins were captured inside the fin stubs while it was stowed in the aircraft. The fins were deployed as soon as the bomb left the aircraft. This was achieved using compressed nitrogen to drive a single axial piston and four connecting rods, activated by a lanyard. The Valiants themselves were also fitted with six retractable dragon’s-teeth ‘fingers’ at the leading edge of the bomb bay to disturb the airflow to avoid the ‘nose-up’ effect which generated lift.
The main casing of the bomb was fabricated by Hudswell Clarke at Leeds. The firm is best known for design and manufacture of industrial steam locomotives. They made the transition to aircraft, bomb and—later—rocket production through sub-contract work from November 1938, initially to Blackburn Aircraft’s Olympia Works on Roundhay Road, Leeds. The firm took over the works when Blackburn moved to Brough. They also made the centre section and nose of the various trial models, for which the tails were made by Follands.
The nature of the work at Hudswell Castle was apparent to the workforce:
Every man on the shop floor would know what they were working on, because inside the Blue Danube tail joint ring (and other similar items) was a small brass plate engraved with the customer’s name (Atomic Weapons Research Establishment) and a serial number. No one was so dumb as not to know who that was, even in 1956.
Suspension system—Percival Aircraft
The suspension system for Blue Danube also shows how practical aspects of the technology were devolved to the RAE at Farnborough and onward to individual private contractors. A process of distributed problem solving which allowed HER at Aldermaston to get rid of their responsibilities for the delivery system. Again it involved the most unlikely participants.
The physics package had to be suspended inside the ballistic case and insulated from the severe vibration and buffeting the bomb would experience on a jet aircraft during take-off, climb and cruising in the cold upper atmosphere. Structural design of the centre section of the bomb was undertaken by Percival Aircraft of Luton. There were hefty aluminium front and back formers for the cylindrical centre section of the bomb casing. These were separated by a horizontal structure—a rigid but light ‘strong ring’ made of cast magnesium with a circular hole to provide multi-point support for the sphere
The outside of the explosive sphere was cushioned on thirty-two airbags matching each segment of explosive. Each airbag had an opening to allow for insertion of the detonator. This patchwork of air bags was held in place by a hinged aluminium cover, again made up of the same combination of pentagonal and hexagonal plates. The plates were laced together with substantial piano hinges attached to each plate edge and threaded together by hinge pins of 20 gauge steel wire. This surface covering of tessellated plates spread the weight of the explosive package under gentle tension. The centre of each plate was also open to a detonator cap of about 6 inches diameter. Lugs were fixed on the cover plates all around the equator. The lugs were fixed to the strong ring by attachment bolts. In this fashion, the whole explosive sphere, weighing close on three tonnes, was gently and evenly suspended under slight pressure within a cosseting layer of air.
The butyl rubber airbags surrounding the explosive sphere were made by William Freeman& Company Limited in Barnsley, a well-known hot-water-bottle manufacturer. Reg Milne recalls:
Dai Williams suggested air bags. I chose the rubber. I went to two firms, India Rubber, Gutta Percha and Telegraph Company where London City Airport is now and to a firm up in Barnsley. Now they made Suba-Seal hot water bottles amongst other things. They were a lot more accommodating and competent we thought. We settled on them.
Reg Milne’s choices show the flexibility inherent in the devolved structure of decision-making. However, in contrast to the openness at Hudswell Clarke:
I am quite clear that Freeman and his salesman and staff had no idea of the purpose of the air bags—just that they were important and needed promptly. They were made in the same workshop with moulds made to fit in the presses that were being used for all the other products.
Fuzes
Technical development of the various fuzes used by Blue Danube was given over to Royal Ordnance at Woolwich, along with the related firing mechanism and detonators. The slow development of the whole firing circuit highlights the troubleshooting necessary to convert design ideas into workable technology. Their slow delivery became a bottleneck and prompted design reappraisals. The electronics of Blue Danube shows how design often evolves by solving a sequence of problems, only in this instance the technology was already in service.
To ensure the bomb imploded, there were a variety of fuzes, all with duplicate circuits. The fail-safe approach made the circuitry complicated. Blue Danube was a free fall bomb built for an air burst in either a ‘high’ position at 2450 ft or ‘low’ position at 1082 ft. Detonation was triggered by a ground proximity fuze (or W/R fuze)—a simple form of radar located in the nose of the bomb. Since each fuze was duplicated there were four proximity fuzes in the service weapon, arranged as a quadrant. To add to the difficulty, contracts for manufacturing these devices were divided for security reasons. Two outside suppliers—Plessey at Ilford and Peto-Scott at Weybridge—were responsible for supplying the proximity fuzes. In addition, Woolwich made the first fuzes used on the trial weapons. To add to the complexity, a clockwork time fuze was added, again duplicated. If all else failed, either a graze fuze or a contact fuze detonated the weapon when it hit the ground.
Supply was insufficient. So a ‘crash programme’ had to be set up in January 1955 to supply the ground proximity fuzes. This initiative seems to have been highly effective and the whole programme went up a gear during 1955 as the RAF Valiants were being commissioned. A design freeze was imposed. No more modifications were allowed. Production was switched to the Royal Ordnance Factory (ROF) at Burghfield. Key staff were loaned to suppliers. It was a classic instance of troubleshooting.
Ironically, a shortage of clockwork delayed matters. A government evaluation of Blue Danube ruefully remarked: ‘instead of the supply of radio-active bomb components being the limiting factor, this doubtful distinction belongs to the Firing Installation and the Time Fuse’.
Detonators and firing mechanism
Detonators were one area where US experience helped UK development. US technicians Luis Alvarez and Lawrence Johnston developed exploding wire detonators for ‘Fat Man’. These bridge wire detonators had the advantage they would vaporize simultaneously in microseconds in a predictable and precisely timed way thereby avoiding an asymmetric explosion where plutonium leaked out of one side of the sphere without forming a critical mass. These detonators were developed and tested at Fort Halstead but their manufacture was given to AWRE production unit located on Ha-Ha Road, Woolwich.
Development of the firing circuits, fuzes, secondary fail-safe fuzes and circuits was led at HER, Fort Halstead, by W. J. ‘John’ Challens, a former rocket scientist and future director of AWRE. This was frontier technology. Firing circuits provided a precisely timed high-voltage pulse to reach all thirty-two detonator sites at exactly the same moment. To this end, all of the firing cables were the same length. This meant detonators close to the firing unit had a length of excess cable coiled nearby. These firing circuits were to prove problematic, illustrating a familiar truth that it is often the subsidiary aspects of a technology that stand between success and failure, not the main technical principle itself.
Multipoint detonation of the thirty-two detonators was achieved with a high-voltage pulse. The firing mechanism had to discharge a precisely timed pulse to all of the detonators simultaneously. This posed novel design problems. Details are partly classified, but it seems various designs were used. Early components shown to the author discharged a bank of eight condensers (now known as ‘capacitors’). These are devices which store an electric charge until required. They were prompted to discharge their pulse by a very large relay driven by the fuze current. Later photos show a pulse transformer which may be part of a more reliable design. (Pulse transformers are not dissimilar to the magneto once fitted to cars.) This too would need to be moderated by condensers to prevent arcing. But limited evidence and newly released documents suggest there were a variety of components used at various stages in the evolution of the weapon. In particular, there were problems with the unreliability of condensers.
The electrical pulse to the detonators needed to be discharged in less than a millisecond, requiring a very fast switching device. This was achieved using a trigatron, a glass valve filled with gas which ionizes instantly as a plasma, thereby allowing a current to pass through. It switches ionically, just like a flash of lightning. Trigatrons were widely used in radar as transmit/receive switches during the Second World War, but only had to perform at low altitudes, and even so were prone to explode. The design of trigatron for Blue Danube was altered at a crucial stage and maintenance records for RAF Barnham show they were temperamental in service use.
A trigatron switch has another advantage. An electric pulse is usually a drawn-out distribution of current. (Consider the slow pace at which an old light bulb element illuminated when switched on.) A trigatron trims the slow build up and run down of current, giving a short, sharp burst instead. This current was then fed to the detonators.
These circuits were novel in the laboratory. The problem was to produce a reliable circuit which gave simultaneous switching regardless of temperature or air pressure, even after long periods of storage and despite vibration in flight. Just to make sure it worked, the firing mechanism was duplicated. As was remarked ‘By the very nature of the blast every effort had to be made to get 100% reliability’.
Potting—a potted history of problems
High technology often stumbles on prosaic problems. Delivery of an atomic bomb posed new challenges for electronics. V-bombers were to fly at high altitudes and currents spark across gaps at the low air pressure existing at high altitudes. Flying high meant components cycled from warmth at ground level to extreme cold at high altitude—shrinking with drop in temperature. V-bombers were to be deployed in areas of high humidity, such as the tropics, bringing the problem of moisture ingress. Circuits would vibrate during take-off and flight creating mechanical stresses to break connections.
The solution to these problems was encapsulation of electronic components in resin through the arcane art of potting. This pioneering technology evolved in the late 1940s, but was not without shortcomings. It is difficult to get resin to bond to the components. Cracks and tracks might emerge as the resin shrinks giving alternative routes for stray currents. The durability of resins was not clear. The very process of encapsulation set up forces in components which could break soldered circuits. To add to the embarrassment, preparation of resin could be exothermic and resins would melt through plastic containers and heat up components. Many circuits which performed perfectly under test failed once they were encapsulated for use. For instance, a report on the proximity fuzes concluded: ‘cracking of a percentage of valves in Araldite blocks is envisaged’. The teething problems associated with potting are illustrated by attempts to manufacture the firing system.
Volume production of the firing mechanism was first entrusted to Whiteley Electrical Radio Company of Mansfield, Nottinghamshire. Whiteley was a private company founded in 1926 which specialized in loudspeakers for domestic radios and public address systems. Whiteley was an unlikely candidate for a crucial military electronics contract. However, the firm did have a vertically integrated production system, including electromagnets which were a key component of Blue Danube’s circuitry which amounted to a ‘mass of relays’. They would have set aside separate production facilities for the secret work.
Components of the firing unit included a power supply, a trigatron to switch the pulse, a pulse transformer, a trigger isolator and an arming unit. This was coupled with a trigger unit, a discriminator and a junction box. Everything was duplicated and all wired into a common frame behind the explosive sphere. Surviving units show components were built up on a frame and then substantially encased in transparent resin. Individual electronic components came from a range of UK manufacturers, including Norbury Watch Co. who made the trigatrons and BICC who supplied the eight specially designed EHT condensers for each unit.
An initial order was issued to Whiteley in Mansfield for assembly of components in 1953 but there was insufficient detail for a complete contract; so the actual contract was not issued until 8 January 1954. Even then design details were not finalized. There were constant modifications up to the point where none of the twenty-five initial sets of firing units had been delivered by the end of 1954. By that time Blue Danube bombs had been delivered into RAF service. So the electronic component supply chain was a severe bottleneck. The contract with Whiteley began at an initial value of £255,000 but soon doubled as the modifications flowed in. Individual components proved unreliable and there were no agreed test procedures. In the meantime, firing units were being delivered by the research laboratory of ARE(C) at Woolwich Common as a stop-gap measure. Indeed, the first complete and fully tested production firing unit was not delivered from Mansfield until July 1955. All firing units had to be tested in Stratosphere Cabinets. Sub-units passed individual tests and were successfully built up into sub-assemblies only to fail on final assembly of the complete mechanism once ‘potted’ in Araldite. Arming Units, Trigatrons and EHT condensers were prone to failure at this stage.
By the end of December 1955 Whiteley had still only delivered twenty-six firing installations out of the 120 planned. This was not helped by a change in Trigatron design in July 1955. The contract was finally rescinded in 1955 and ended in acrimony with the Ministry of Supply going to court to recover two stratosphere test cabinets loaned to Whiteley and not returned.
The firing system contract was taken up by Dennis Ferranti Meters, at Bangor. The firing system for an atomic weapon presented an opportunity for new business to an aggressive newcomer. The firm specialized in precision assembly of meters. They had no experience of electronic components. Nevertheless, in 1955 a contract was issued for fifty-six firing units for £200,000 which proved successful. The components were assembled and tested amid great secrecy in a department with its own dedicated workforce, management and security ‘minder’.
Physics package
Conventional explosives were central to the workings of Blue Danube. A carefully structured globe of high explosives was needed to initiate the implosion. Casting of the segments of the fabricated high explosive ball was initially delegated to the Royal Arsenal, Woolwich and the resulting spheres were taken to Foulness in Essex for testing. But full-scale production moved to Royal Ordnance Factory (ROF) Chorley in June 1953. The ball was made up of pentagonal and hexagonal sections which tessellate together to form a sphere. The outer explosives were built up as ‘lenses’ so as to focus the blast on the centre of the sphere. During manufacture, the explosives were poured as liquids into moulds in two stages to form the lenses. When solidified, shaped lenses of RDX/TNT curved outside the inner cones of Baratol.
The plutonium core of Blue Danube remains secret, but it is clear the design evolved from that used by the original ‘Fat Man’ device. The warhead assembly was altered in service once practical shortcomings in arming the weapon became apparent. This evolution is illustrated by the development and demise of IFL which resulted in a redesign of the casing, a change in arming procedures on the ground and the warhead assembly being turned upside-down.
Originally, with IFL, Blue Danube was assembled and loaded into the aircraft without its plutonium core. The first operational bombs were deployed on Valiant aircraft. The bomb was loaded and fixed precisely and firmly into the bomb bay with a 2-inch clearance below to allow the bomb doors to close. The bomb was locked into place using the same device employed for Second World War Tallboy and Blockbuster bombs on the Lancaster. This had two curved S-shaped arms locked into place at the top by a gudgeon pin. There was an access hole in the top of the bomb casing to allow IFL to operate.
IFL was promoted as a safety device to avoid an accidental yield or contamination. This inherently safe concept owed much to John Rowlands who was seconded to HER, Fort Halstead, from the RAF. But there was a more pragmatic reason for wanting to see the core separated from the bomb in flight: if the bomb had to be jettisoned, the precious plutonium core was retained on the plane.
The arming device was initially loaded into the plane from above through a hatch on the top of the fuselage. A vertical box section inside the fuselage above the bomb bay contained the mechanism for inserting the core into the bomb. At its lower end, the loading device rested on the edges of an opening in the outer shell of the explosive of the bomb. A bayonet connection locked the insertion mechanism into the sphere by a push and turn action. The loading device allowed for movement of the bomb relative to the aeroplane.
The arming device—or cartridge—was a slightly tapered test-tube-shaped device like a geological core sample. It contained the spherical plutonium core of the bomb at its base (with its initiator) plus a complete vertical bore through the rest of the sphere including a section of the uranium tamper and segments of the two types of explosives. When the IFL was actuated, an electric motor pushed the arming device into the heart of the sphere from above, inserting this missing section of the sphere precisely between the detonators. Once this transect plug was inserted, the bomb was complete and symmetrical and ready to be dropped. As the bomb fell away, the hole in the top of the bomb was closed by a spring loaded ‘finger chopper’ plate stowed just behind the hole.
The IFL was designed, and then redesigned at RAE insistence, by Frazer Nash. The electric actuator motors were made by Miles Aircraft at Shoreham, with a built-in brake. A pair of actuators was used, coupled by a differential, to drive the vertical movement using two helical screws.
Considerable technical effort went into refining the design of the IFL system by the RAE even after it was installed on Valiant. IFL was not adopted for Victor and Vulcan aircraft and abandoned sometime after summer 1956 for reasons which are not clear, but standing on the slippery back of a Valiant on a snowy, cold night handling a heavy cartridge containing radioactive material and explosives would not have been an attractive job for two aircraftsmen. IFL was replaced by Last Minute Loading whereby a Navigator-Radar from the flight crew inserted the necessary cartridge into the bomb from below to make it live just prior to take-off. This system too was not without its shortcomings.
Deployment and storage
New technologies require new operating practices. Quite apart from new bombers and new strategic doctrines, the Royal Air Force had to develop a new set of routines to handle nuclear weapons, including armed convoys to move bombs around and ‘special storage’ facilities at depots and airfields. A new set of procedures was developed for the loading, arming and release of the weapon. These new measures forcibly illustrate the radical nature of the atomic bomb as an innovation in warfare.
These routines were developed under the leadership of the Herod Committee (‘High Explosives Research Operational Distribution’) and the related Salome Committee. A special training school was set up at RAF Wittering called the ‘Bomber Command Armament School’ (BCAS), formed on 1 August 1953 under Wing Commander J. S. Rowlands to train aircrew and engineers in the use and servicing of nuclear weapons.
Two ‘special storage sites’ were built at RAF Barnham in Suffolk and RAF Faldingworth in Lincolnshire to store and carry out simple maintenance on Blue Danube. The ‘top site’ store at Barnham, south of Thetford, was operational for just ten years between 1953 and 1963. Blue Danube was made up a small fissile core and a large high-explosive sphere. This combination of radioactive material and high explosives dictated the layout of the site at Barnham. Within the inner compound or ‘danger area’ there were three high explosive storage sheds for the casings and explosives known as the DD Buildings. There were also four sets of individual ‘igloos’ for storage of the plutonium cores distributed around the site, totalling fifty-seven in all. There was a central maintenance building and another much smaller building for maintaining the weapons. The site is built around a circular inner road. The secure area is surrounded by a concrete panel security fence and an outer chain link fence a kilometre long with watch towers at each corner. The ‘free fire’ zone between fences was patrolled by armed guards. In common with other Cold War installations, the bomb store is on a large scale.
Igloos for core storage were simple concrete shelters about 2 metres high fitted with wooden doors, remote alarms, secure door locking and a circular stainless-steel locked safe fitted into the floor. The cores were light and compact and amenable to manual handling so these storage huts were spread around the site reached by narrow concrete paths. In contrast, the heavy bomb carcase required road access, travelling cranes and mechanical handling devices (although the overhead gantries at the DD sheds were seldom used). Since the bomb casings contained high explosive, lined with their uranium tampers, the three large concrete-framed sheds had side walls that were not bonded into the pillars or the roof. In turn, these sheds were surrounded by earth banks to help contain and deflect any explosion upwards. These sheds were air-conditioned. Typically the bombs were stored in a fishbone pattern on their trailers allowing swift removal in the event of fire.
New routines were developed for handling the new atomic bomb. There were always two RAF personnel in charge of handling or releasing a nuclear core. To release a core from storage needed an ‘Equipper’ with the combination of the igloo and an ‘Engineer’ with the key to the padlock of the safe inside. They would then walk together with the core to the load carrier. Casings were always transported separately from cores. Again, the two-man principle was always used on the aircraft: the ‘NavRadar’ would release the bomb, but the Captain controlled the bomb release safety lock on the final pin preventing the bomb dropping.
Supply chain: manufacture, assembly and delivery
It is clear the Blue Danube supply chain shifted over time as various manufacturers gained competence and a Royal Ordnance Factory site at Burghfield in Berkshire emerged as an assembly centre, taking over from Chorley. Sections of the weapons were transported to RAF Barnham or RAF Faldingworth for onward deployment to V-bomber airfields in the UK and Cyprus or retained for ‘second strike’ storage. There were many curious features to these covert logistics. For instance, the tail was assembled in Nissen huts at a semi-derelict ROF site at Elstow, south of Bedford. Entrance to this unguarded and unmarked site was concealed behind rusty gates in a hedge off a roundabout on a main road.
Conclusion: evolution of a technology
Blue Danube was the first British nuclear deterrent deployed during the Cold War carried by the V-bomber force. Here we consider how the bomb was designed, procured, manufactured, assembled and delivered to airfields and bomb stores, focusing on the practical evolution of the technology. Production of components was widely distributed across the public and private sector in England and Wales.
Focus on the fissile aspects of atomic weapons development means the difficulties of making the whole weapon have been overlooked. It was a struggle to develop and manufacture reliable electronic components, notably the fuzes and firing units. There was an acute shortage of electronics components three years after the weapon was first supplied for operational use. Ironically, deployment was constrained not by lack of fissile material, but by a shortage of simple, clockwork-based time fuzes.
So, development of Blue Danube is a story of paradoxes. Problems with high explosives turned out to be as much a constraint on serviceability as the novel fissile material. Extraction of weapons-grade plutonium was described as a ‘brilliant success’. Yet, HER struggled to design the complicated explosive jacket for Blue Danube.
In broader terms, the story here contradicts conventional accounts of technical development. The ‘linear model’ of development suggests science leads to technology, then to prototypes, on to testing and design and then closes to a reliable final product. In contrast, Blue Danube was an imperative of ‘build first-test later’. Many components were only tested and reliably manufactured after the weapon was delivered. The operational weapon was modified, as if it were a prototype. There were two different ‘priming’ systems and casings during the bomb’s brief history. Production decisions were often based on rules-of-thumb and judgement rather than science and experiment. Blue Danube was more a process of learning than a finished product. It was deployed first and developed afterwards.
Our account shows aspects of atomic weapons technology were distributed across agencies such as the RAF, the RAE, the Ministry of Supply and a range of manufacturing firms. There was a strong interlock between the military needs and the civilian economy. The many innovations needed to bring the weapon into use were spread around the UK. Blue Danube’s practical development was a product of a wider ‘warfare state’ of Cold War Britain, not just the product of a few boffins. In truth, the first atomic bomb was designed in suburban centres and built in ordinary factories down prosaic back streets by regular workers—men and women—in towns across industrial Britain. The atomic bomb was the product of northern industrial towns and the suburbs of southern England as much as the secret citadels of Fort Halstead, Aldermaston and Burghfield.
So, Blue Danube was a provisional deterrent—frequently modified as problems cropped up. Blue Danube continued to evolve after it was designed. In this respect it was also a learning deterrent as the RAF developed new routines and the supply chain learned how to manufacture and maintain nuclear weapons. It was also a half-way house deterrent as those who had been at Los Alamos knew of the possibility of a fission-fusion weapon, an H-bomb.
Above all, Blue Danube—however provisional—was a British deterrent. The weapon was developed and deployed with awesome professionalism and with emphasis on the credibility of the threat it posed. Cheap but practical development of the atomic bomb saved deploying resources elsewhere. As Peter Barker said of ARL’s Drawing Office:
We joked that somewhere there must be a large brilliant team—with boundless resources—doing the ‘real job’, and that we were just a decoy […] it was inconceivable that ARL’s small-scale activity could possibly be a major part of the development of the British Nuclear Deterrent.
It kept the UK rather forcibly in the great power game and encouraged the Americans to renew cooperation over nuclear secrets. But the triumph of the technology was as much prosaic as scientific.