Violet Club - The first high yield weapon deployed by the British

Brian Burnell explains the use of Nuclear weapons on his website www.nuclear-weapons.info.

This blog extracts some of the information relating to the development and testing of Nuclear weapons and the extensive research that has been undertaken by Brian and a team of researchers.

Concentrating on Violet Club, which was the first high yield weapon deployed by the British, and was intended to provide an emergency capability until a thermonuclear weapon could be developed from Christmas Island thermonuclear tests known as Operation Grapple.

After the Americans tested a thermonuclear weapon in 1952, followed by the Soviets with Joe 4, and before the UK government took a decision in July 1954 to develop a thermonuclear weapon, AWRE Aldermaston was asked in 1953 about the possibilities for a very large pure fission bomb yielding one megaton. AWRE's response referred to the Zodiak Mk.3 bomb but progressed no further than a rudimentary study.

At this time studies were also started that ultimately led to a decision in 1954 to develop a thermonuclear weapon, and the design studies were split into two tracks, the Thermonuclear Bomb Type A, a hybrid type, really a very large boosted fission device, no longer regarded as a thermonuclear weapon, and the Type B, a device that derives a significant amount of energy from fusion.

The British at that time had not yet discovered the Teller-Ulam technique necessary to initiate fusion, and the Type B was still beyond their capabilities. The intermediate devices proposed, the Type A hybrids, were similar in concept to the Alarm Clock and Joe-4 layer cake hybrid designs of other nuclear powers. Although these Type A intermediate devices used small quantities of fusion fuel in their fissile cores to provide a supply of energetic, fast neutrons to boost the efficiency of the fission reaction, they did not derive a measurable amount of energy output from fusion.

The Violet Club warhead, known variously as Green Grass, Knobkerry, and the Interim Megaton Weapon was a pure, unboosted fission device derived from the two British Type A weapons, stripped of their fusion boosting elements. It was the largest pure fission weapon deployed by any nuclear power.

Design defects

Violet Club and Green Grass were not considered satisfactory designs and suffered from numerous design defects, some, in the case of Violet Club's casing, being inherited from the Blue Danube casing that had itself suffered from numerous defects. Many of these were attributable to it being the first British nuclear bomb, and it being the first bomb to be designed for release from aircraft flying at the great heights and speeds envisaged, and there was no experience of bomb release at more than twice the height and speed of the previous generation of medium bombers.

A major defect was the reliance on batteries for all electrical power after release from the aircraft. The batteries used were 6v lead-acid accumulators, - commercial motorcycle batteries, that were kept fully-charged and inserted into the weapon on the ground immediately before flight. In Violet Club they were used to charge large capacitors in the warhead firing circuits and provide power to the Blue Stone ENI (External Neutron Initiator). Both were essential components of the firing circuits. Storing the batteries outside the weapon while on the ground was thought a necessary safety break between the power supply and the firing circuits, but contributed to lengthy delays while the batteries were inserted at the last minute before flight.

Later generations of weapons used ram-air-driven generators that provided no power prior to release, or thermal batteries that could be safely stored in the weapon for lengthy periods without maintenance, and the necessary safety break was provided by other means, eg speed detectors activated only by bomb release.

Other design flaws, the rushed Service entry and uncertainty about shelf-life of the weapon led to a requirement for a complete strip-down and inspection at six-monthly intervals. Each taking three weeks per weapon using AWRE civilian staff. The unstable nature of the weapon, with the fissile core being greater than one uncompressed critical mass, required that the work being done in-situ at RAF bases, causing considerable disruption to operational duties.

Three principal reasons for the strip-downs were deterioration of the rubber bag lining the inside of the hollow spherical core, that was in intimate contact with the steel balls, corrosion of the steel ballbearings, which exacerbated rubber bag deterioration, and deterioration of the HE, which was prone to cracking. Replacement of the HE would cost RAF budgets in excess of £92,000 adjusted to 2007 prices.

The RAF was under considerable pressure to find adequate storage for the weapons at operational bases because the weapon was too unstable to be transported by road to suitable specialist weapon storage facilities or to be stored in close proximity to other similar weapons. One weapon per storage building was the rule. Strip-down inspections were a further hindrance to their operational duties, seriously jeopardising essential safety and servicing work on tactical nuclear weapons.

Deployment and carriage

Deployment was to be at RAF Wittering and Vulcan squadrons at RAF Finningley and Scampton, although at Scampton a problem arose because there were no suitable storage and workshop facilities on base at Scampton. The weapon was to be stored nearby at Scampton's off-base specialist weapon storage and maintenance facility at RAF Faldingworth, seven miles away. The embargo on transport of assembled Violet Club weapons on public roads was a subject of much head-scratching, and there are declassified files that show that an exception was made for this site.

The first weapon was delivered in April 1958, and the fifth and last was due for delivery on 27 November 1958, although there are suggestions that this date may have slipped to May 1959, just in time to be retired from service.

The carriage was by Vulcan medium bombers only, the Victor being later into service, with release at high altitude only, using the same techniques as adopted for Blue Danube. The Violet Club casing had identical ballistic properties to Blue Danube to minimise development time and cost.

RAF dissatisfaction

Violet Club/Green Grass struggled to meet the Chiefs of Staff requirement for a high yield Interim Megaton Weapon as specified with a megaton range yield. It was a cobbling together of elements of at least two other designs, Green Bamboo and Orange Herald, both inherently unstable designs, each with fissile cores that were greater than one uncompressed critical mass. A hastily devised nuclear safety mechanism added to overcome the warhead's inherent instability was less than adequate to ensure safety in several scenarios identified by the RAF.

One such scenario was that of an aircraft fire while a Violet Club bomb was loaded in the aircraft with the safety balls removed. The best advice AWRE could offer was to drench the area with fire retardant while lowering the weapon to the ground for a quick getaway. Or lowering the weapon to re-insert the steel balls. Without the steel balls inserted, a road traffic accident on the airfield that crushed or deformed the hollow spherical fissile core was sufficient to initiate uncontrolled fission. With 1'500 lbs (689 kg) of HE in the bomb, a large 'dirty bomb' was a real possibility and contributed to the restrictions on road movement on and off base.

Violet Club had to be armed before flight and take-off was likely to be hazardous, and therefore the weapon couldn't be used on an airborne alert, and couldn't be jettisoned when armed. Landing on return to base with an armed bomb was too hazardous to contemplate. The aircraft's bomb release mechanism's ferry flight weight limit of 11'100 lbs was inadequate for the bomb with the ballbearing safety device installed, so Violet Club couldn't be flown to a remote dispersal base in accordance with RAF strategy planned for periods of heightened international tension, and that was a source of great dissatisfaction for the RAF, because the dispersal plan was central to RAF strategy.

Strategic Air Command bomber bases were mostly located deep within the North American landmass and had considerable warning time before short-range missiles launched from off-shore could reach their bases, and had adequate time to scramble their aircraft. Unlike SAC, all ten RAF Bomber Command main bases were within range of short-range missiles launched from off-shore or Eastern Europe and had only minutes after receipt of warning in which to scramble their aircraft. The ten main bases were therefore supplemented by twenty-six dispersal airfields, located from Kent, close to the English Channel, to Cornwall, Wales, and Ulster in the west, to the northeast, and the Western Isles of Scotland.

At times of international tension, bombers were to disperse with their weapons around these distant airfields. Violet Club, being unmovable by road when assembled, unarmed, and not able to be flown unarmed to the bomber's dispersal airfield, effectively wrecked RAF's strategic dispersal plans. The RAF were aware of these shortcomings when they agreed to accept Violet Club as an emergency capability weapon for a short period, with the proviso that after approximately one year a more developed variant of the Green Grass warhead fitted into a better, modern casing, Yellow Sun, would be introduced.

It would have in-flight arming with a mechanism to jettison the steel ball safety device only if the bombers were ordered beyond their fail-safe point. RAF chagrin was in large part because that improved weapon was never produced, and the Green Grass ground-armed warhead installed in Yellow Sun casings soldiered on for four years, until 1963, after the Cuban Missile Crisis, with the RAF unable to disperse its bombers.

The warhead installed in Violet Club was never proof-tested, and AWRE estimated its yield at 500 kilotons, based on the Christmas Island test of Orange Herald. Mr W.J.Challens of AWRE who later became the Director of AWRE claimed to the Air Staff that it met the specification because

" A weapon of one half megaton is considered to be in the megaton range."

A statement that returned to haunt AWRE when later estimates revised the yield downwards to 400 kt. Challens also stated to the Air Staff on behalf of AWRE that

 " AWRE were almost completely sure that a nuclear explosion would not occur if the balls are in - but in the absence of trial-proof he could not guarantee it."

It is hardly surprising that his qualification of 'almost' did not instill confidence in the Service users, and the non-nuclear elements of the weapon were not adequately tested either, as this RAF Bomber Command instruction indicates.

" Aircraft engines must not be run with Violet Club loaded on the aircraft with the safety device [ of steel balls ] in place. The engines must not be started until the weapon is prepared for an actual operational sortie." [ to prevent the balls vibrating like a bag of jellybeans. ]

" ... uncertainty exists about the effects of movement with the balls inserted."

Other engineering specialists were also unimpressed with the warhead. Dr S.Jones, writing on behalf of the Armaments Dept at the Royal Aircraft Establishment at Farnbourgh described the nuclear safety device as a:

" very unsatisfactory type of nuclear safety device that was essential for Green Grass ... "

A senior officer, an Air Commodore, the Director of Operations at Bomber Command, writing on 26 Jan 1959, referring to the flight preparation time and recall after take-off said:

" I think the twenty minutes required to make the weapon 'ready' [for take-off] impacts on Bomber Command's plans to no small extent: and it is not very 'safe' once this action has commenced. Return to base after recall, may be hazardous. We want a better safety device."

A Wing Commander at RAF Bomber Command, a Bomber Operations staff officer, minuted his senior, the Air Commodore quoted above with this comment, dated May 1959:

" This minute means that Violet Club and Yellow Sun [both with the Green Grass warhead] are not "in the megaton range" at all, notwithstanding the extraordinary measures taken and costs involved for what we thought to be a megaton capability. This ... leads me to the belief that the production of Green Grass be curtailed. I cannot imagine any commercial organisation continuing to buy a device that so patently fails to meet the requirement, or to be misled without protest as the Air Ministry has so consistently been by AWRE."

Summing up, senior officers at RAF Bomber Command believed they

"had been sold a lemon"

and an expensive one too.

Retirement

All five Violet Club weapons were retired by the end of May 1959. The warheads were removed and retrofitted to the new Yellow Sun Mk.1 casings, where they were to be adapted for in-flight removal of the steel ballbearing nuclear safety device, using the smaller balls. These plans for in-flight arming were never implemented, the equipment was never deployed, and the Green Grass warheads from Violet Club were transferred to Yellow Sun Mk1 casings intact.

The failure of AWRE and RAE at Farnborough to implement the in-flight arming plans was a source of much of the dissatisfaction expressed by senior RAF staff officers, partly because of safety concerns; partly because of servicing issues; but mainly because the RAF Bomber Command dispersal plan was unusable.

The casings were scrapped, and none survive in museums. The five Green Grass warheads from Violet Club with a further thirty-two warheads built for Yellow Sun Mk.1 survived until 1963 when all were replaced by thermonuclear warheads of American design.

About Brian Burnell

Brian was employed there as a (very) junior design engineer, initially charged with making tea and being a 'gofor' (translates colloquially as in "go for some fish and chips").

Over several years from 1955 he worked on Violet Club, Blue Danube, Red Beard, all the Maralinga and Christmas Island airdrop test casings, and numerous other less well-documented projects, both in the design offices, workshops and assembly areas, with access to every aspect of the weapons.

At the end of 1958, shortly before I moved on to work on new projects, Chief Designer Shaw and the Production Manager (a higher form of gofor) received their reward, in the form of a gong, (a medal to my non-British foreign readers) an award of an MBE each in the New Year Honours List, making both of them Members of the British Empire.

Presumably awarded on behalf of us lesser mortals who did the actual hard graft behind a drawing board. There were no computers then, at least not for lowly engineering staff! Not even a pocket calculator had been invented. The best we had was a set of log tables and a slide rule. But we managed OK I believe; without any terrible accidents.