Previous efforts Vickers-Armstrongs had been developing guided missiles from the earliest stages of UK research in the field, setting up the Guided Weapons Department at
Weybridge (Brooklands) in
Surrey. By the mid-1950s had been involved in four projects, all of which were cancelled. The last, the
Red Dean/
Red Hebe air-to-air missile was so delayed and over-designed that the company began to have a bad reputation with the
Ministry of Supply, especially with
John Clemow, the Director. When Red Hebe was cancelled in the aftermath of the
1957 Defence White Paper, the company's guided missile department had no remaining projects. Unwilling to give up on the missile field,
George Edwards led an effort to find a new project that could be undertaken with company funds alone. This led them to the ideas of John Housego and Jal Daboo for a lightweight anti-tank missile. They were already aware of the
British Army's unhappiness with the recently deployed
Malkara anti-tank missile, and felt there was an opportunity here. In 1956, Edwards convinced the board to take up the development of a replacement for Malkara using a new guidance system developed in-house.
Earlier designs Malkara was one of the earliest anti-tank missiles, and had several problems. Primary among these was the Army's ongoing interest in the use of large
high-explosive squash head (HESH) warheads instead of the more common
high-explosive anti-tank (HEAT) used by most anti-tank weapons of the era. For any given level of penetration, HESH required much more explosive, and Malkara's need to deal with
main battle tanks demanded a warhead. Combined with the long desired range, , the missile ended up being , far too heavy to make it
man portable. The guidance system was also less than ideal. This consisted of a small joystick that the operator used to guide the missile while visually comparing its position with the target, aided by a bright
flare on the missile. When the operator pushed the stick to the right, for instance, it operated the control surfaces to turn the missile to the right. The problem was that the missile would continue moving to the right after the control was released, eventually crossing the
line of sight, continuing onto the right side of the target, and then requiring left input to stop this motion. This often led to the operator repeatedly overcorrecting the path of the missile, which required significant amounts of training to overcome. The same basic guidance system was used by most contemporary designs like the
ENTAC,
SS.10 and
SS.11, and the
Cobra, as well as the
US Army's experimental
Dart that was not put into production. Another problem with all of these designs was their size. They all traced their development history to
WWII-era German experiments with the
Ruhrstahl X-4 in the anti-tank role [the
X-7]. These used
spoilerons as controls, with limited control authority. In order to provide enough lift to manoeuvre the missile at reasonable speeds, very large wings were needed. This resulted in bulky designs that were large and impractical for carrying manually.
Development begins Sure that a contract for a Malkara replacement would be forthcoming, Vickers hired John Clemow, their critic, along with Howard Surtees, to head up the new effort. Development began in late 1956 under the model number 891 and given the name Vigilant, for VIsually Guided Infantry Light ANti-Tank missile. Setting the range at , half that of Malkara, greatly reduced the size of the rocket motor required. They approached
Imperial Chemical Industries (ICI) who developed a lightweight motor with the required performance. In order to reach their desired weight, the missile would have to use a light HEAT warhead. An advanced model had been designed by the
Royal Armaments Research and Development Establishment (RARDE) but had not been released to industry, so an off-the-shelf design from the Swiss firm Constructions Méchaniques de Leman (CML) was chosen instead. The guidance system consisted of two parts. The first was a gyroscope that measured the "up" direction and changed the control outputs so that the correct control fins were actuated no matter what angle the fuselage was compared to the ground. This allowed the missile to spin along its long axis, which was used to even out any asymmetry in the rocket thrust and ensure it flew in a relatively straight line. The second part used two gyroscopes that measured the azimuth and altitude motion, referenced to the ground plane of the first gyro. This set was the key to the improved guidance system. If the user inputs a correction to the right, for instance, this motion would be seen in the horizontal-measuring gyro. When the control was released, the guidance system would input left control until the gyro was zeroed out again. This resulted in the missile always returning to a line of flight pointed directly away from the operator. To guide the weapon, the operator controlled it left or right until it visually overlapped the target and then released the control. The missile would automatically continue along that line until it hit the target. The second gyro, measuring the vertical motion, kept the missile flying level above the ground and mostly eliminated the need for vertical corrections during flight. This system had the added advantage of eliminating the effects of wind or remaining asymmetry in thrust. With the autopilot providing smooth control, the need for slow-acting controls seen on earlier missiles was eliminated. Instead, the new design used large conventional
ailerons that could point the missile as much as 30 degrees away from the line of flight. At these sorts of angles, the rocket motor itself was producing significant control thrust, allowing the wings to be much smaller. These were in the form of long short-chord rectangles that maintained lift at very high
angles of attack. This led to a much more compact design. Another idea in Vigilant was that the missile launcher was connected by a long wire to the guidance control. This allowed the launcher to be set up in any open location while the operator moved to a location with more cover. After launch, the operator would guide the missile into his line of sight and then correct it onto the target. Although the missile left a smoke trail back to the launcher, that was far enough from the operator to offer protection. Targets could be up to 40 degrees to either side of the launch position.
Testing Uncontrolled tests were first carried out in the summer of 1957. The first examples of the guidance system were test fired in September 1958. By this time the original germanium transistors from
Texas Instruments were replaced by silicon versions, which were both less expensive and much less sensitive to temperature.
Mullard, the UK subsidiary of
Philips, also took up production of the same transistors that year. Further improvements the next year allowed all temperature variation to be ignored, removing the need for
Zener diodes that had provided this function. Testing also demonstrated that the guidance wires were not strong enough and tended to break, leading to extensive experiments to find a solution. The rocket exhaust impinging on the wire tended to pull the wire off the spool early in flight, so the spool arrangement was changed to avoid this. Another change was to the form of the controller. This was originally in the form of a "Sten gun" like arrangement that was designed to be fired from the hip during the testing phase, but modified for use while prone for the production version. In testing it was found that the operator would input the incorrect vertical guidance command about 50% of the time, up instead of down for instance. After some experimentation a new design was developed used that used a cup-like arrangement that the operator inserted the front of their thumb into while their fingers held a pistol-like grip. In this version, guiding the missile down was accomplished by pulling the controller down, as opposed to pushing forward as on a conventional joystick, and the problem of incorrect guidance immediately fell to only 5%. By March 1959, thirty-five missiles had been fired in tests. By this time, US interest in replacing their SS.10 missiles was becoming serious, and the
US Army intended to make a decision in early 1959. To meet the requirement, Vickers scheduled a series of twenty launches at Weybridge between 9 and 20 March 1959 that would be followed by another five at
Fort Benning. It later became obvious that the test equipment at Benning was not really suitable for the tests, so a series of twenty-seven tests was carried out at
Redstone Arsenal instead. Testing at Redstone noted that the flare was too difficult to see at long range in bright sunlight, and a more powerful model was developed.
Official disinterest While testing in the US was leading to a possible order, the British Army proved not only uninterested, but in some ways, actively hostile. In a 1959 memo, it was stated that "We would not be justified in encouraging the Company to maintain their guided weapon design capacity" and while any number of studies included Vigilant in their discussions, there remained no official plan to buy a light anti-armour weapon of any sort. This discouragement was due to the ongoing changes to the industry in the aftermath of the 1957 Defence White Paper.
Duncan Sandys strongly suggested that future orders for weapons would only be given to larger companies, forcing the merger of smaller firms. Among these was the merger of
English Electric and Vickers that would form the nucleus of
British Aircraft Corporation (BAC), later adding
Bristol Aeroplane Company and
Hunting Aircraft. EE and Bristol already had their own successful missile design teams, and the government felt there would be no need for a third. Any encouragement to Vickers at this point was seen as a problem if that team would later be broken up and merged into the other two. To break the logjam, Vickers arranged a 29 September demonstration of the system with 200 officials invited to attend. Eleven missiles were fired for seven hits. It was only at this point that the lingering problems with the wires breaking were clearly on the way to being fully solved, and changes to the simulator system and training regimen were paying off with the average miss from the aim point of only . The demonstration was a success in terms of starting some official consideration of supporting the project. After discussion of purchasing a dozen missiles, later enlarged to two dozen, an 11 January 1960 minute encourages this and compares Vigilant to the French SS.10, SS.11, ENTAC and German-Swiss Cobra, with the Vigilant being highly competitive with all of these. A 22 April memo represents a setback, reiterating the original concerns, followed by a 28 April memo suggesting the Army had not yet decided whether a soldier could effectively operate the system. By this time, the formation of BAC was well underway. On 30 May, the new director of BAC's guided missile programs wrote the
War Office and flatly stated that the company would be keeping the Weybridge office open. The memos continued to fly and it was not until 4 August that the War Office finally conceded the point and decided to offer small contracts to keep the effort going. The news was made public on 26 August, the newspapers noted the company has spent nearly £1 million on development and the projected price was only nearly £500 per unit.
Intro production The Army had long expressed its concerns about the capabilities of the CML warhead against
main battle tanks and both the Army and Ministry continued to consider the system in a negative light. By 1960, the
Swingfire program was in its initial stages, and was already considered the ultimate anti-tank weapon. Swingfire aimed to address any shortfall in performance with a much more powerful warhead. The planned future development of a scaled-down version, "medium-range Swingfire", was intended to be a more portable version that would fill the same role as Vigilant. At almost the same time, the Army Council noted that there was a need for new anti-tank weapons for use by the
British Army of the Rhine and forces in the
Middle East. In particular, they suggested there was an immediate need for an anti-tank armed version of the
Ferret armoured car to serve these roles. While medium-range Swingfire could fill this role, the original Swingfire was not expected until 1966, and the medium-range version sometime after that. They compared ENTAC and Vigilant to arm Ferret and concluded Vigilant was markedly superior to ENTAC due to its guidance system. On 7 November, a contract was offered to fill the "firm and urgent requirement" for the Ferret. This led to an order for seventy additional missiles for tests starting 1961. The matter of a wider purchase remained open and it was not until 24 November 1961 that clear signals from the Ministry of Aviation suggested they were going to fund production. BAC quickly issued a press release, which almost immediately led to several additional orders from foreign users. By this time the merger of Vickers into BAC was starting in earnest, and through the early part of 1962 the Weybridge design office closed with most members moving to Stevenage.
New warhead As the Vigilant pushed through development and an order seemed forthcoming, in May 1962 the Army began development of a new warhead at RARDE that significantly improved penetration. This was effected primarily by moving the
contact fuse to the end of a "probe" that extended forward from the front of the missile after launch, providing more stand-off distance in which an improved metal jet could form. Similar concepts are used by a number of anti-tank weapons to this day. Penetration figures for the British-designed warhead are not known, it was never released for export and only the CML versions were sold abroad. In testing, British Aerospace found the CML warhead was able to penetrate of typical single-layer tank armour. It also proved capable of penetrating
spaced armor consisting of a plate, a gap, and another plate. These sorts of armor thicknesses were much in advance of most tanks on the battlefield, which at that time were generally much thinner; even the
T-72 of a decade later had maximum armor in the turret front of 280 mm. As well as infantry use, Vigilant could be mounted on vehicles such as the Ferret and
Land Rovers. For airborne troops, a lighter polystyrene foam container was developed as well. ==Description==