Vickers Vigilant
The Vickers Vigilant was a British 1960s era MCLOS wire-guided anti-tank missile used by the British Army. It was also licence-built in the United States by Clevite for the US Marine Corps, and sometimes known as Clevite rounds in this case.
Development began at Vickers-Armstrongs in 1956 as a private project to give the company's Weybridge Guided Missile Department something to do after the cancellation of Red Dean. By 1960 it had completed development and an extensive testing program, but the War Office remained disinterested as they wished for the Weybridge department to be disbanded as part of the ongoing formation of British Aircraft Corporation. On several occasions the Office explicitly stated they did not want to provide any encouragement to the team as this might make it harder to close the division down in the future.
After considerable debate spanning several years, the project eventually won an initial order as it was the only suitable design to arm the Ferret armoured car. By this time the War Office had already decided that their ultimate weapon for this role would be the Swingfire, but it would not be available until 1966 at the earliest. An order for several thousand Vigilant was placed late in 1961 as an "interim weapon". The order immediately resulted in several additional orders from Kuwait, Saudi Arabia, Libya and Abu Dhabi, along with Vigilant-armed Ferret sales to the UAE and Yemen. The order also sealed the US decision to license Vigilant for local production.
Swingfire did not arrive until 1969, and during that time the medium-range man portable version had been dropped. This left the Vigilant in use with the infantry and airborne forces well into the 1970s. Approximately 18,000 were produced in total.
History
Previous efforts
had been developing guided missiles from the earliest stages of UK research in the field, setting up the Guided Weapons Department at Weybridge 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 warheads instead of the more common high-explosive anti-tank 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 . 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 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 but had not been released to industry, so an off-the-shelf design from the Swiss firm Constructions Méchaniques de Leman 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.