September 02, 2004

Precision Munitions 

What happened to my intentions of writing of science technology? I feel more like the usual political pundit.

Thus, let's go back to business, and talk about precision weapons!

Precision munitions are also called "smart weapons" - in opposition to "dumb weapons". But I don't like that expression very much, because it is not very accurate, and in translation its meaning can become distorted.

Let's start with defining a conventional (or dumb) munition - or weapon. That is a weapon with no guidance system whatsoever. Bullets, bombs and rockets, once they left a gun's barrel, once dropped from a plane, or once the propellant is exhausted, will follow a ballistic trajectory until they will eventually impact something or the ground.
A ballistic trajectory is determined by the initial speed and direction of the moving body, by its aerodynamic characteristics and by the properties of the medium (usually air).
This means that factors like imperfections of the ammunition, wind and other phenomena will cause scattering of the shots.

Some non-guided munitions are however extremely precise: sniper rifles can put a shot within a radius of few centimeters at 1000 m, and artillery shells will land within a few meters from the aimed point at something like 30 - 35 km.

Other weapons, like aircraft bombs and ballistic rockets (like the infamous Russian series Frog) have much poorer performance. The Frogs will land in an area of a few square kilometers around the aim point. Modern unguided bombs can hit much nearer the target, but they need to be dropped from low altitude, exposing the aircraft to anti-aircraft fire.

During WWII, the Allied strategic bombers dropped from considerable altitude, attempting to avoid anti-aircraft fire (the dreaded FLAK). The bombs went easily astray, and in order to hit any target, the bombing raid was designed to saturate with bombs an area around the target(s). Sometimes, it was even impossible to locate a target (like a refinery) - remember, no satellites, primitive (by our standards) radios and radars, no ground observers, so the commanders decided to bomb the whole area where the target was. The hit ratio was awfully low; maybe 1:10, even less sometimes, but the allies had plenty of resources to throw in the fight.

However, this kind of air bombing is very expensive in materiél and men: thousands of planes were downed, tens of thousands of airmen died or were injured during the raids on Europe and Japan, and later in Korea and Vietnam - even if at that time early guided bombs were available. Carpet (or area) bombing also causes huge destruction and non-combatant losses on the ground - I don't need to remind you the horrible devastation of Europe and Japan after WWII. On the other hand, Baghdad seems almost untouched by the recent fighting.

On the other hand, artillery was already mature in the WWII era, and its performances have not increased much since then - except for the very recent development of rocket shells and guided projectiles.

Rockets were used extensively by more or less any party of the war, in surface-to-surface, air-to-surface, and even air-to-air roles. All of those (as far as I know) were unguided rockets, especially the infamous Russian Katyusha. The German V-1 (missile) and V-2 (rocket, and a big one too) were instead guided; the V-1 with a very rudimentary system to measure the length of flight; the V-2 had a more sophisticated inertial guidance system.

And, carpet bombing cannot be used to provide air support to ground troops (excessive risk of friendly fire), and it's scarcely effective against small-sized and/or hardened targets. Even more, aero-naval battles needed desperately precision bombing: an aircraft carrier cannot haul a whole bomber squadron and the bombs and fuel needed to carpet-bomb another naval group. Thus, towards the end of WWII, both Americans and Germans developed the first guided bombs.

The American model had control surfaces, a cable link to the bomber and a tracer cartridge at the tail: a crewmember in an apposite combat station equipped with control devices could spot the tracer light, and through the cable link manually guide the bomb to its target. These bombs were used against the Thailand-Burma Railway.
I don't know the details of the German guided bombs, but they were used to sink the Italian Navy's battleship Roma, towards the end of the war.

By 1956, the Sidewinder heath-seeking air-to-air missile was born, and military pilots had to start watching out for a new threat.

The first laser-guided bombs were used during the later stages of Vietnam war (I think so), but by no means extensively. The first significant use of guided munitions came later, with the Gulf War (the first one, if you like), where these new weapons proved highly effective. Also in that era the myth of almost-infallible bombs was born. In part because some military overplayed the performance of the new weapons; in part because ignorant journalists did not understand what were they about and were looking for a scoop, that myth was born, and now the anti-war guys are still sneering at the "smart bombs" everytime one goes off target.

The main advantage of guided bombs is that they can be dropped from higher altitude, or farther away from the aim point, and still impact on (or very near) the target. Thus, a target can be destroyed with a few (in the best case, one) bombs, with less risk for the aircraft and its crew, and less collateral damage on the ground.

The laser-guided bombs (LGB) have a sensor which can see laser energy reflected by the target, and feed data to the flight control system, homing towards the target. The illuminating laser beam comes either from the same aircraft which drops the bomb, from another aircraft or a designator team of ground soldiers. The whole subject is fairly complex, and a LGB can miss the target in case of human errors, if the designating aircraft must evade swiftly (as if fired upon), if the beam is scattered or reflected by smoke, dust or mist. In situations of low visibility, LGBs are less effective. Then, it may happen that pilots simply make a mistake in identifying the target. The bomb will work properly, but the target is the wrong one.

There are also TV (or IR) guided bombs, and these will find their way using a visible or infrared camera mounted on their nose. Those bombs are currently being upgraded with GPS guidance systems.

The latest advance is the GPS guided bomb. Actually, more than a new bomb it is a inertial/GPS guidance kit (JDAM) that can be bolted on a Mk-80 series free-fall bomb, giving it outstanding capabilities. The target coordinates are uploaded in the bomb's electronics, and after release the munition will receive GPS signals in order to calculate its position and maneuver towards the target. The GPS system is not affected by bad weather or smoke, and it is very difficult to jam. One of these devices can be dropped from 10 000 m, and still fall within a few meters of the target, on unsuspecting and helpless foes.
The GPS systems will be integrated with optical, radar and IR guidance systems in order to obtain even greater accuracy and flexibility for a variety of missions.
JDAMs have been used extensively in the recent Afghanistan and Iraq wars with excellent results. Precision munitions, in fact, are suitable for close air support, because the risk of friendly fire is minimized. With the help of highly trained ground soldiers, advanced sensors and communication devices, even small groups of hostiles, single safe houses and vehicles can thus be targeted, giving to the US military unprecedented capabilities against guerrillas.

Of the special bombs, the famous Bunker Buster is laser-guided, while more modern hard target penetrators will probably have GPS and laser guidance.
Anti-radar bombs simply follow the beam emitted by a radar transmitter.
The Daisy Cutter is unguided and parachute-stabilized. In contrast, the dropping aircraft must be accurately positioned.
Cluster bombs are currently unguided, but it's in the plans to fit also them with GPS units.

Missiles already use more or less the same guidance systems as bombs (air-to-air or surface-to-air missiles use peculiar guidance systems): laser, radar, IR, TV (a missile can recognize landscape features and compare them with a memorized image of the target and surroundings), inertial and nowadays GPS. Cruise and long-range missiles often use one guidance system for mid-course and another, more accurate, for the final approach.

Up to now I wroe about US weapon systems. Russia uses similar systems, but I don't know if they have access to military-grade GPS signals (the GPS satellites are US-owned).
Europe, China, Israel and other nations have developed their own weapon systems, but they basically are based on the same technologies. Most of Arab countries can only buy foreign-made weapons, often Russian or Chinese. However, the US is currently the undisputed leader of high-technology weapons.


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