Violet Club: Quite Possibly the Worst Nuclear Bomb Ever Fielded

The warhead, or physics package, of the Violet Club bomb

When taking a look at the development of British nuclear weapons following the Second World War, it has to be viewed in the context of a piece of legislation in the United States that was passed in 1946- the McMahon Act or the Atomic Energy Act. Sponsored by Senator Brien McMahon of Connecticut who chaired the Senate Special Committee on Atomic Energy, this legislation is better known for its creation of the Atomic Energy Commission and the placement of nuclear weapons development and nuclear applications under civilian rather than military control. However, one consequence of the McMahon Act was the stipulation that nuclear weapons development be restricted from US allies- this affect the United Kingdom and Canada who had provided scientists and support to the wartime Manhattan Project. As a result of being shut out of American nuclear weapons development, the British set about to create their own air-dropped weapon which would be fielded in 1953 at RAF Witttering- though somewhat amusingly the first aircraft that could carry the bomb, designated Blue Danube, the Vickers Valiant, didn't become operational until a year later. The purpose of this wasn't just a message to the Soviets, but also to the United States that Britain was more than capable of fielding its own nuclear deterrent despite the McMahon Act. 

On 1 November 1952 the United States detonated its first fusion bomb (H-bomb) in the Ivy Mike test at Eniwetok Atoll in the Pacific. Given that the British were still shut out of US nuclear development by the McMahon Act, despite the fact that the Blue Danube fission bomb (A-bomb) was still a year out from being operational, strategic imperatives meant that Britain had to develop it's own H-bomb and the program was launched in 1954. In the UK, many military systems were assigned code names under the Ministry of Supply's "rainbow codes"- hence, "Blue Danube". In the development of an H-bomb, the casing had its own code name and the actual warhead, called the physics package, had another code name. The casing of the H-bomb was based on the Blue Danube casing and was designated Violet Club while the physics package was designated Green Grass. 

But before the code names had been settled upon, the British H-bomb had a different name- "Interim Megaton Weapon"- implying that it was a high-yield weapon but not a true thermonuclear or H-bomb/fusion weapon. And this is really at the heart of the history of the Violet Club and its historical legacy. First, it indicates that Violet Club was intended to be a temporary weapon and secondly, it wasn't a fusion bomb as was commonly believed by *both* the Soviet Union and the United States. 

The warhead or physics package of the bomb was based on earlier warhead designs that were named Orange Herald and Green Bamboo. Orange Herald was a lighter version of Green Bamboo and the designs were projected to be the new fusion warheads for the Royal Air Force's V-force, the Blue Steel stand-off missile, and the planned Blue Streak intermediate-range ballistic missile. Testing of Orange Herald showed that it had failed to boost the fission reaction to create a fusion reaction. The failure of the warhead designs left the British scrambling for a high-yield weapon and this became the Green Grass warhead of the Interim Megaton Weapon that was based on design elements of the earlier Green Bamboo and Orange Herald designs. As was the case in the United States, interservice rivalries in Great Britain meant that the Army wanted highly enriched uranium (HEU) for nuclear landmines in Europe and the Royal Navy wanted HEU for the reactors for its planned nuclear-powered submarine fleet. The Royal Air Force was of the feeling that the HEU that had so far been produced in British reactors had to be used or it would be lost to rival services, so that was one of several motivations to rush the Interim Megaton Weapon into service as it would use a significant amount of HEU.

Schematic of the Green Grass warhead showing how the ball bearings were used.

It was the design of the Green Grass warhead that went into the Violet Club that made it for all practical purposes a useless weapon. A hollow sphere of HEU was surrounded by a system of 72 explosive lenses that compressed the HEU to critical mass and detonation. But here was the problem. In the Green Grass warhead, the mass of HEU was in *excess* of the critical mass once compressed by the explosive lenses. That meant if the warhead were crushed or damaged during handling, it could partially detonate. American designs avoided this by having an HEU core that was inserted into the physics package usually by the bombardier once the bomber was in flight, thereby "arming" the bomb once the core was inserted. Without the core inserted, the HEU mass in the American designs was below the critical mass. The solution by British designers was to fill the center of the HEU sphere with 20,000 steel ball bearings to prevent the sphere from being crushed and reaching critical mass. To arm the bomb, a plastic plug was removed from the bottom of the warhead (accessible via a hatch on the underside of the Violet Club casing) that allowed the bearings to flow out, thereby arming the bomb. 

While it may sound like a creative solution, there were several issues: 

• The weight of the ball-bearings increased the bomb's weight to 11,250 lbs which was greater than the capacity of not only the bomb release mechanisms of the V-bombers but also the ground-transport equipment of the bomb. 
• The outflow of bearings took at least half an hour under ideal conditions- in cold weather, the bearings could freeze together, making arming the weapon near-impossible. 
• Once the bomb was armed by allowing the ball-bearings to flow out of the center of the warhead, there was on way of making the weapon safe again. In fact, engine running was prohibited even with Violet Club "safed" as it was feared vibration would cause the plastic plug to fall out and inadvertantly arm the weapon. 
• Because the bomb was armed irreversibly, airborne alerts were impossible because take off and landing were too hazardous to attempt with an armed Violet Club. 
• Dispersal of the V-force to outlying fields was impossible as the bomb couldn't be flown to the dispersal airfield and the bomb transport equipment couldn't handle the Violet Club when it had its ball-bearings in place. 

The Blue Danube- the Violet Club looked similar externally.

While the Air Staff of the RAF ordered twelve Violet Club bombs, only five were made and as British author Chris Gibson put it in his book Vulcan's Hammer "From the RAF's point of view, that was five too many." With such an unwieldly weapon, why was it even fielded? First of all, remember that the British were classifying the Violet Club as megaton-class weapon by calling it the Interim Megaton Weapon. It definitely wasn't a megaton weapon, perhaps more 400 kilotons at best, but certainly the Operation Grapple tests at Christmas Island in 1957 did indicate to the Americans the British were succeeding at fielding their own H-bombs- even if those test detonations failed to created the desired thermonuclear reaction. So who was the target of the Violet Club? While serving notice to the Soviet Union that Britain was still a force to be reckoned with, it seems that perhaps the Americans were the target, so to speak- with a weapon in their inventory called Interim Megaton Weapon implying that newer designs forthcoming and the Grapple series of tests in 1957 making a good show of things despite failing to work as planned, in 1958 the United States repealed the McMahon Act and resumed full nuclear cooperation with the United Kingdom. The Green Grass warhead used in Violet Club would be the last all-British nuclear weapon as a new Mutual Defense Agreement signed as part of the repeal of the McMahon Act meant British designers now had access to more advanced and compact American designs. In fact, the successor to the much-despised Violet Club, the Yellow Sun Mk.2, used an Anglicized American Mk.28 thermonuclear warhead. But no other fission weapon ever fielded by any other nation approached the explosive yield of the Violet Club.

Source: Vulcan's Hammer: V-Force Projects and Weapons Since 1945 by Chris Gibson. Hikoki Publications, 2011, p47-51. http://www.nuclear-weapons.info/vw.htm, by Brian Burnell.

The Canceled British Aircraft that Cost the UK Industry

I bet you thought you were going to be reading about the BAC TSR.2 when you came across the title of today's post, but while there's no arguing the effects that the TSR.2 cancellation had on the British aerospace industry, there was a canceled aircraft that came before the TSR.2 that some have argued cost British industry far more than could ever have been imagined. In 1951 the government had issued a specification for a new long range strategic transport that would be able to move 120 troops long distances to replace the elderly piston-powered Handley Page Hastings. It was envisioned that this new transport could also move personnel and equipment rapidly around the world and deploy as necessary with the new V-force bombers that were soon to enter service with the Royal Air Force. The main condition of the specification was that it had be based on existing design. 

Five companies submitted proposals, with Bristol submitting a version of the Britannia turboprop transport, Saunders Roe submitting a variant of their Duchess flying boat, and Handley Page, Avro, Vickers, and Short submitting transports based on their bomber designs (Victor, Vulcan, Valiant, and Sperrin, respectively) and powered by the new Rolls-Royce Conway turbofan. De Havilland submitted a stretched version of its Comet 1 jetliner. Bristol's Britannia variant was eliminated early due to it being too slow, along with Saunders Roe's flying boat. The Sperrin was next eliminated as the transport version had a fuselage only 9 feet wide with accommodation for only 50 passengers or personnel. Handley Page and Avro's submissions were judged too risky for the RAF contract, leaving only Vickers and De Havilland as the remaining designs not eliminated.

It was realized early on after Vickers was named the winner of the RAF competition that what the RAF needed was not terribly dissimilar with BOAC's need for a long range jetliner that offered more capacity and range than the De Havilland Comet 1. The original specifications that Vickers won was then amended with the requirement that the jet transport also earn a certificate of airworthiness from the civil aviation authorities. With the new amended specifications in place, an order was placed with Vickers for the V1000 prototype aircraft, serial number XD662, in March 1953. 

The V1000 would be the RAF transport version and the anticipated civilian version was the VC7. With construction of the V1000 prototype underway in the summer of 1954, the RAF ordered six aircraft with an eventual requirement of twelve aircraft. BOAC was regularly consulted through this phase as they wanted to put the VC7 on the North Atlantic routes to Canada and the United States as well as on the longer Empire routes that couldn't be served by the Comet 1 jetliner. Besides BOAC, Trans Canada Airlines (Air Canada's predecessor) and Pan American showed significant interest in the VC7. Even BEA expressed an interest in the VC7 for its longer European services.

To meet BOAC's wishes, the V1000/VC7 was a bit larger than the RAF desired, mainly out of a need for the wing fuel capacity to meet BOAC's range requirements. Four Rolls-Royce Conway engines were mounted in the wing root similarly to the Vickers Valiant only the wing was larger and more swept with Kuchemann wingtips (similar to the 707-320BAdv and 707-320C's wingtips) and low mounted. The fuselage had six-abreast seating with a 12.5 foot diameter. This was significant at the time, as Boeing was wrestling with the cabin diameter on its anticipated Boeing 707 and Douglas at the time was still contemplating five-abreast seating for its coming DC-8. Unfortunately prototype construction at Vickers' Wisley facility showed that the V1000 prototype's weight would be about 18,000 lbs higher than planned.

It would have been a simple matter to have upgraded the Conway turbofans, but for whatever reason, BOAC's enthusiasm for the VC7 cooled as the planned weight with the intended engine would rule out London-New York nonstop services. Ironically, several years later when BOAC ordered the 707-430, it would have Conway turbofan engines that were upgraded that would have worked on the VC7! Government meetings in September 1955 formalized BOAC's disinterest in the VC7 and suggestions were made that De Havilland put forth a stretched version of the Comet as well as refinements to the Bristol Britannia as being suitable for BOAC's needs. In addition, BOAC looked further ahead to the mid-1960s for a possible supersonic transport. Despite BOAC's incomprehensible stance, Vickers anticipated the V1000 prototype's first flight in June 1956 with the first production aircraft flying in 1959 with inaugural airline services in late 1959/early 1960 (not too far off from when the Boeing 707 began its passenger services). In a bid to maintain the competitiveness of the VC7, Vickers explored other engine options and even looked at a version of the VC7 with each of the Conway turbofans in its own podded nacelle under the wing, not unlike that of the 707 and DC-8's layout.

By this point the RAF was entering a period of fiscal austerity and it's most expensive item to date was the V1000/VC7 project. Without mentioning the V1000/VC7, the British government cautioned the RAF to scale back its expenditures. Politics came into the picture with the prospect of the end of Comet production which would have affected one of the Comet's main subcontractors, Shorts in Belfast. A desire to keep Shorts busy shifted the support amongst some MPs in Parliament against the Vickers jetliner. In addition, the Britannia was having teething problems with its turboprop engines and was selling slow. Some ministers in the government felt that support should be given to the Britannia program instead of embarking on the all-new Vickers jetliner. 

Some historical accounts point the finger at BOAC for planning to procure US jets from the start and with the support of some in the government, did what it could to commit formally to the VC7. A spirited debate in Parliament dragged on for weeks with the supporters of the Vickers projects openly declaring that the VC7's cancellation would "give the large jet market to the Americans for the next 20 years". Rather obtusely, several government officials proclaimed that the planned performance of the Boeing 707 and DC-8 would make them cost-prohibitive for many of the world's airlines and the speed advantage over the Comet and Britannia would not matter to most passengers! With the V1000 prototype 75% complete, the project was ordered shut down by the British government on 11 November 1955, and this was despite intensive lobbying by Trans Canada Airlines. 

For many observers, it was the cancellation of the Vickers VC7 and not the TSR.2 where the British aerospace industry lost its way. Sir George Edwards, managing director of Vickers and the chief designer of the V1000/VC7, had lamented that BOAC and the government had simply handed over the lead in jetliner technology to the Americans for "generations to come."

Source: Stuck on the Drawing Board: Unbuilt British Commercial Aircraft Since 1945 by Richard Payne. Tempus Publishing, 2004, p38-42