Air-to-surface tactical missiles

During the 1970s the development of air-to-surface missiles for tactical uses experimented a notable progress, above all regarding anti-ship, anti-radar and precision guidance systems. Here starts a chapter in which, as it happens with a good share of the history of missiles, the origins are found in revolutionary projects realized by German technicians and scientists during the two world wars.

It could be thought that fitting a functional guide system in an air-to-surface missile is a simple task. It could be said that since bombs fall simply by effect of gravity, they could be stabilized by incorporating fins on them and easily directed by appropriate movements of those fins. It is a logical conclusion, but the first developments of missiles of this category - which as in the case of other types were born in Germany - choose in their beginnings the configuration of an airplane. After the Second World War a wide range of these weapons was developed, which happened in part due to the complexity of the task of creating adequate guidance systems. This article describes only air-to-surface tactical missiles; the strategical missiles of this category have a range greater than 160 kilometers and are often fitted with nuclear warheads, which in tactical missiles are rarely used. Before considering the problems posed by a guidance system, it is essential to decide which would be the purpose of the missile. With few exceptions, the first missiles of this type were developed to reach small targets that were beyond the possibilities of free-fall bombs. Among such targets, bridges had a prime position, but there were as well many others, including warships and merchant ships. A factor that largely contributed in the development of this then new weapon was the anti-aircraft defense. The well defended targets discouraged the utilization of bombers or even fighter-bombers, which tried techniques to reach the targets with a reasonable probability of surviving the defenses, such as dive attacks and runs at low altitude upon the target. In some cases there were air-to-surface missiles whose precision was lesser than the one of free-fall bombs, but they could be launched from much greater distances, decreasing or nullifying the danger posed for the launching aircraft by dense anti-aircraft defenses.

Siemens was the pioneer

Without any doubt the most important program of missiles developed before the Second World War was the one directed by the company Siemens-Schuckert Werke (SSW) during the First World War, destined mainly for the German Imperial Navy. Doctor Wilhelm von Siemens suggested the creation of a remote-controlled glider bomb in such early date as 1914, two months after the start of the war. The company had already considerable experience with remote-controlled boats and the project advanced at good pace. Flight tests, directed by engineer Dorner, started in January 1915, with increasingly larger gliders. In every case control was effectuated by means of an electric control, using thin copper wires that were unrolled from a coil. The servoactuators used intitially as energy source a conventional battery, but since mid 1916 it was used a wind generator, which used a pinwheel that rotated when displacing at high speed on the air. The control of rudder and elevators was effectuated by transmission of binary commands, allowing only two extreme positions without any modulation between both, so rudder and ailerons remained in the last position that had been commanded from the two possible ones. After a good number of tests, it was conceived as well a method for having the fuselage opened in two sections when receiving the corresponding command, allowing so to drop a torpedo carried within.

The tests were carried from the factory Siemens in Neumunster, in the spring 1915. Night tests were effectuated from August 1916. After 75 flight tests with large biplane gliders, the Navy prepared an airship and so were started the flight tests with biplanes and monoplanes weighing 300 kilograms from the Zeppelin Z.XII in the surroundings of Hannover, in April 1917. Later were effectuated flights with gliders from airships L.35 in Juterbog and Parseval Pl.25 in Potsdam. The L.35 transported later numerous gliders of 500 kilograms and some ones of 1000 kilograms. The last flight corresponded to a glider torpedo SSW number 7, the 2nd August 1918. It flew 7.6 kilometers after being freed at an altitude of 1219 meters, but the double command wire got broken when the gliderwas already upon its target, about 60 meters above it. In the time of the Armistice - November 1918 -, SSW was starting more advanced tests in the airbase Nordholz, using low-profile monoplanes, with a wingspan between 4.17 and 5 meters. It was also expected to launch these pioneers of the modern air-to-surface missiles from bomber aircraft built by SSW as well. Among these, the R.IV showed itself as unsuitable, but the R.VIII - the largest bomber of the First World War - could perfectly carry these monoplane gliders. Launching tests had not been started when the Allies forced to discontinue the works in December 1918.

Deficiencies of the first missiles

From 1943, Germany used systematically several models of air-to-surface missiles, in quantity of several hundreds, which in turn stimulated the development, in United States, of "glider bombs", "vertical bombs" and other contraptions, most of which suffered from basic deficiencies. In the last 18 months of the Second World War, the United States Army Air Force (USAAF) deployed missiles of this type in England, Italy and Burma, but they were seen with mistrust and many were never used. After the war, the first truly effective use of air-to-surface missiles took place in Korea, when the powerful guided bomb Tarzon was launched from bombers B-29 over bridges, dams and similar targets, in the border with China. The subsequent systems that entered service were the Bullpup of the United States Navy (USN) and a growing family of French weapons, developed by a company successively denominated SFECMAS, Nord and Aerospatiale. As almost all of the air-to-surface missiles of this time, they had to be telecommanded by an operator to keep them aligned with the target until the impact. From the 1950s many of these missiles were developed and still they had obvious deficiencies. The most serious one was that, despite precision could be improved in respect of free-fall bombs, the exposition of the launching aircraft to the anti-aircraft defense was not only not reduced, but it could even be increased, since the aircraft was forced to go after the missile to guide it. Which actually was required - and this had been already specified in a report from the Luftwaffe, from 1943, and another one from the USAAF, from January 1944 - was a missile of the so called "fire and forget", fitted with an autonomous guidance system that would not require any external support once the missile were launched. After the launching, the carrier aircraft could dedicate itself to perform the pertinent evasive maneuvers to escape anti-aircraft fire instead of attending the trajectory of the missile.


Scheme of the Fritz X missile, showing the armored piercing ogive; such strong ogive was intended to perforate the thick armor of a battleship. The 9th September 1943, two of these bombs launched from bombers Dornier Do 217, sank the battleship Rome and severely damaged her twin Italia.

Seeking the perfect guidance system

One of the most important objectives of the air-to-surface missiles is the neutralization of ships, and multiple were the guidance systems used for this purpose. The most simple one was based in the visual and identificative ability of the operator directing the missile, who guided the artifact looking at it and to the target with bare eyes and modifying the course by means of a pertinent signal link, such as radio emissions or wires. Later, it was installed in the nose of the missile an electro-optical or television-based seeker. Once in the vicinity of the target, the seeker was locked onto it. Then the missile would be launched and it would head towards the position that had been previously set. This system was useful for a direct attack, most suitable against a static target. For an indirect attack, useful against a moving target, the missile was launched and directed to the area of the target by the operator, who used a television screen to see the image sent by the camera installed in the nose of the missile. By means of the pertinent command link, the missile would be maneuvered until being locked onto the target when this one was nearby enough. But this method could pose a problem. Both the emission of television signals from the missile and the radio signal transmitted from the aircraft to guide the missile could be interfered by the enemy by means of electronic countermeasures. In this regard, a connection by cable was much safer, but this method is only possible for slow and short-range missiles. As far as possible, the best approach to design a guidance system would be to exploit a source of radiation emitted by the target itself. Either radar signals or thermal emissions were used to create new guidance systems that would automatically direct the missile towards such emission sources, from a distance of several kilometers.

Countermeasures

The enemy could employ diverse resources against such systems: extensive use of electronic countermeasures, infrared countermeasures - either passive ones, like thermal covers, or active ones, like lure flares -, deactivation of the source of emissions or any other mean able to unlock the guidance system. Disconnecting the radars was the simplest way to fool anti-radar missiles, and with this method the North Vietnamese successfully counteracted the anti-radar missile Shrike during the Vietnam War. But soon the more modern air-to-surface missiles were fitted with a memory bank that allowed them to fulfill their trajectory regardless of the source of emission being disconnected. Still, the target could use active countermeasures to confuse the missile directing it towards a different target. Hence, the ideal would be to exploit a radiation source that could not be distorted by the enemy. The subsequent answer to this question was the laser: vanguard troops could be equipped with laser designators, with which they would "illuminate" the targets with a continuous and invisible ray. Then the missile fitted with a laser seeker would be able to automatically reach and hit the target. Albeit many of the laser systems operated in very exact wavelengths, they were developed as well modulated systems, allowing to hit certain targets exlusively with certain missiles.

Three large groups

Basically, there are three main groups of guidance systems, which use either long waves (infrared systems), medium waves (radar systems) or short waves (laser systems) of electromagnetic radiation. Probably the simplest system was the one developed by Texas Instruments for the "smart bombs" Paveway, introduced during the Vietnam War. These were conventional free-fall bombs which had incorporated in their ogive a guidance unit, fitted with four fins that were operated by means of a command system controlled by external signals sent from four low-sensitivity silicon detectors, disposed in a quadrant mounted in a separated conical sensor, which was orientable in respect of the tip of the guidance unit by means of an universal joint. When the bomb was launched, the sensor aligned itself with the course of the wind, hence being always aligned with the direction that the bomb followed. When the sensor detected the target it started to send signals to the control fins, balancing the data from the four detectors and keeping the sensor pointed directly towards the target that reflects the laser radiation, so the bomb was automatically directed towards the same point.

Visibility

The laser allows for launchings of great precision. If the target is "illuminated" by first line troops or remote-controlled aircraft, the target can be hit even if there are clouds, smoke or bad weather in general. An alternative that can be used is that an aircraft carries the laser designator and another one the missiles, albeit this method could double the number of targets within enemy range, with the added inconvenience that the destruction of one of them would nullify the attack capacity of both. The last factor that conditioned the development of air-to-surface tactical missiles was the magnification of the human capability to see clearly any combat situation. Albeit both optical and radar-based methods have been exploited to the end, the greater progress in this field s constituted by the infrared rays, which offer thermal images of the heat sources, usually persons and vehicle engines. The most modern attack aircraft - including helicopters - were fitted with infrared sensors to be able to "see" regardless of camouflage, smoke, rain, snow or the darkness of the night. This was an area where the Soviet Union soon achieved a considerable capability, albeit the characteristics of their missiles were largely unknown by the western experts during the Cold War. Infrared-based systems, as the reader can imagine, were also particularly effective for anti-tank missiles, which shall be presented in another batch of articles. During the 1980s, air-to-surface missiles became a weapon of generalized utilization, of which the most important armies possess a large diversity of models, regarding the different tactical possibilities.


Mark 84 bomb enhanced with HOBOS (Homing Bomb System), a system introduced in 1969. The ogive of the bomb can be seen behind the electro-optical system. This was the first version of the HOBOS, composed of a general-purpose 907-kilogram bomb, a guidance section incorporated in the fore part, a control section incorporated in the rear part and an interconnection ensemble to link all the components.

Multiple employment

A very extended employment, particularly after the War of the Falklands, is the one of anti-ship missiles launched from aircraft. Generally, these missiles were initially conceived for surface-to- surface employment, such as the American Harpoon or the French Exocet, and then adequated for air-to-surface employment. Another range of missiles is the one destined to the destruction of puntual targets, those that, such as bridges, command facilities, certain industrial complexes or centers of energy production, require weapons capable of hitting with great precision. Guidance systems such as television cameras allowed to achieve a great precision without exposing the launching aircraft within the range of enemy anti-aircraft defense. Anti-radar missiles were apparently less widespread, but in the event of a conflict it is probable that their usage would become very broad, since they would allow something so important as to disorganize the defense and even the surveillance of the enemy anti-aircraft systems, by the systematic destruction of the radar stations. The last trends - as in the other type of missiles - sought for the effectiveness of the simultaneous launching of several missiles. Instead of having an aircraft limited to attend only the guidance system of a sole missile, having to wait until this one hits its target to effectuate a second launching, more modern avionics granted aircraft the capability of launching several missiles towards the target, using the laser guidance only in the last seconds before the impact.

Categories: Missiles - Cold War - 20th Century - [General] - [General]

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Website: Military History

Article submitted: 2015-01-28