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[1.0] Unguided Bombs & Rockets

v4.0.0 / chapter 1 of 10 / 01 may 14 / greg goebel / public domain

* The modern smart munition is an outgrowth of the traditional unguided or "dumb" munition, which has a long and diverse history. This chapter provides an historical survey of unguided bombs and rockets.

US WWII 4,000 pound GP bomb


[1.1] BASICS OF UNGUIDED MUNITIONS
[1.2] A VERY BRIEF HISTORY OF UNGUIDED BOMBS
[1.3] MODERN UNGUIDED BOMBS
[1.4] A VERY BRIEF HISTORY OF UNGUIDED ROCKETS
[1.5] MODERN UNGUIDED ROCKETS

[1.1] BASICS OF UNGUIDED MUNITIONS

* Unguided bombs come in a wide variety of forms. They can be in the shape of finned spindles or pills, teardrops, or cans, and a few have been built in the form of spheres. They can consist of a single unit, making them "unitary" bombs, or can carry hundreds of small "submunitions" that are scattered over a target area after release, making them "cluster" bombs. Such submunitions can also be carried by "dispensers" that remain attached to the launch aircraft, with the dispenser scattering the submunitions as the aircraft streaks over the target area at low level. The dispensers are often discarded when empty, since it may be difficult to ensure that all the submunitions have been released -- meaning one might pop out when the aircraft lands.

Bombs can be as small as a few kilograms, but the largest one ever dropped in combat weighed 10 tonnes (22,000 pounds). Common modern bomb sizes are 225, 450, and 900 kilograms (500, 1,000, and 2,000 pounds). Bombs can be categorized according to their effects:

Conventional bombs also include chemical or biological munitions; smoke bombs; illumination and marking flares; and practice bombs, which are small, cheap munitions whose aerodynamics match those of full-size bombs. Special dispensers are often fitted to aircraft for the carriage of practice bombs.

* An aerial bomb consists of three main sections: a body that contains the destructive payload; a tail section that provides fins and other aerodynamic devices; and one or more detonating fuzes, which can be at the front, back, or sides of the bomb. These parts are often made in an interchangeable fashion, allowing a bomb body to be fitted with different fuzes or tail sections for different missions. Different guidance systems can also often be fitted to modern bomb bodies to turn them into smart bombs, as will be discussed in later chapters. The task of figuring out how to tailor bombs and other munitions to a mission is known as "weaponeering".

The bomb body varies in size, of course, and varies in structure depending on whether the bomb is a GP bomb, penetrating bomb, cluster bomb, and so on. In most cases the tail section simply consists of a set of fins that stabilizes the bomb's fall. However, with bombs designed to be dropped at low altitude, the tail section provides some sort of "retarder", a drag-producing mechanism that ensures the bomb falls well behind the launch aircraft before impact and detonation. A bomb fitted with a retarder is of course known as a "retarded" bomb.

While little parachutes were used as retarders in the past, today the mechanism consists either of popout fins or, increasingly, a balloon-parachute hybrid called a "ballute" that resembles a conical or pyramid-shaped inflatable tent. Popout fins tend to break at high speeds, possibly pitching the bomb up into the launch aircraft, while ballutes have no such speed restriction.

In comparison to the bomb body and tail section, fuzing is a complicated subject. The fuze technology used with a bomb defines how the bomb is enabled to allow it to explode, or "armed", and what events detonate the bomb. Arming mechanisms include:

Fuzes can be organized according to the detonation parameters that trigger them:

"Smart" fuzes with digital processors and sensors are now available that provide advanced capabilities, such as counting the number of ceilings penetrated in an underground installation and then triggering at a given floor. A bomb may be fitted with multiple fuzes. For example, a bomb fuzed to act as a mine may also have a time fuze so that it will eventually self-destruct, either to harass an enemy or to prevent it from being a hazard to advancing friendly forces.

Reliability of fuzing is an important consideration, since dud munitions can remain a hazard for a very long time -- French and Belgians still have unfortunate encounters with buried World War I artillery shells. This is a particular issue with cluster submunitions, since their numbers and small size making cleaning up duds hazardous. Some cluster submunitions operate as mines, the smaller ones being called "minelets"; they often have time-delay fuzes to make sure they detonate after a time, lest they become a dangerous nuisance to civilians or friendly forces moving into the battle area later.

* Explosive composition, bomb construction, and fuzing are designed to obtain the desired destructive effect, while keeping the bomb safe to store and handle. Clean separation from the launch aircraft is also a concern. Even though a bomb will not be armed immediately after release, it is still a big and heavy object that could do great damage if it pitches up into the aircraft after release.

Additional measures are sometimes adopted to increase bomb safety. For example, after major disasters with ordnance "cooking off" during fires on US Navy carriers during the Vietnam war, the Navy adopted the practice of painting their bombs with a thick ablative coating that would burn off before the bomb detonated.

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[1.2] A VERY BRIEF HISTORY OF UNGUIDED BOMBS

* The aerial bomb was basically invented during World War I. The first attacks on ground targets from the air were performed with grenades, artillery shells, or even jars of nitroglycerine, but building finned bombs specifically for the task proved straightforward. In 1915, Zeppelin raiders over England used thermite bombs to attack British cities. These bombs were conical, consisting of a thermite core surrounded by resin, and wound tight with a layer of rope. High explosive bombs evolved through the war. By the end of the conflict, HE bombs of up to 1 tonne (2,200 pounds) had been built.

World War II led to major refinements in bomb design. The different combatants used a wide variety of high explosive, fragmentation, and incendiary munitions. The Americans used their own series of GP bombs during the war, resembling pills with box fins, in weights ranging from 45 kilograms (100 pounds) to 900 kilograms (2,000 pounds), with 113 kilogram (250 pound) and 225 kilogram (500 pound) bombs being commonly used; a 1,800 kilogram (4,000 pound) bomb was also developed, but saw little or no use. The US also had a range of armor-piercing bombs, as well as small fragmentation and metal-incendiary bombs. Napalm was used late in the war.

US World War 2 fat bombs

Other nations had similar sets of bombs. However, the British developed a series of very heavy bombs, beginning with the "High Capacity (HC)" munitions, with weights from 900 to 5,400 kilograms (2,000 to 12,000 pounds). The HC bombs types were thin skinned, generally lacked tailfins, and resembled boilers; they were informally referred to for some obscure reason as "cookies". They were inaccurate, and so were used to attack cities and other built-up areas. A combination of HC and incendiary sticks were used in the night war against German cities, with the HC bombs wrecking buildings and the incendiaries setting the wreckage on fire.

Lancaster with cookie & incendiaries

Later in the conflict, the British also fielded very heavy "deep penetration (DP)" bombs, devised by the brilliant engineer Barnes Wallis. Large high explosive bombs were proving ineffective in attacks on hardened targets such as U-boat pens. Wallis believed that a more effective weapon would be a big, hard-cased, streamlined bomb that could be dropped on such targets from high altitude, with the bomb exceeding Mach 1 before impact to bury itself deeply and then detonate.

The bomb was fitted with curved fins to ensure that it would be spin stabilized as it broke through the sound barrier and then plunged into the ground. Structures that could withstand a direct hit by the biggest conventional bomb could be toppled by dropping a DP bomb next to them. The blast would blow out huge crater that undermined the target's foundations, and underground installations could be shattered by the shock waves set up by the underground explosion.

The first of these bombs was the 5.45 tonne (12,000 pound) "Tallboy" bomb, which was first used in combat after the Allied landings in Normandy in June 1944. It was slung beneath modified Lancasters and used for attacks on tunnels, V-weapon sites, and other high priority targets. Precise targeting from high altitude was required, and the Tallboy was only used by highly trained crews of RAF Number 9 and Number 617 Squadrons. Its most important use was in the sinking of the German battleship TIRPITZ at anchor in Norway, on 12 November 1944.

Tallboy was followed by a similar but bigger penetration bomb, the 10 tonne (22,000 pound) "Grand Slam". This huge weapon was 7.7 meters (26 feet 6 inches) long. Its hardened casing was cast in a single piece in a sand mold, using a concrete core. The Grand Slam was first used in combat in March 1945. It was effective in destroying targets that had resisted other attacks, such as massive viaducts, by blowing away the ground underneath them. In one raid on submarine pens near Bremen, two Grand Slams penetrated 7 meters (23 feet) of reinforced concrete, bringing down the roof. The Grand Slam remains the biggest conventional bomb ever used in action.

big bombs of World War II

After the war, the US adopted the Tallboy bomb as the "T-10" and the Grand Slam as the "T-14", with both such weapons carried by the big Convair B-36 bomber. The B-36 could also carry a further scaled-up penetration bomb, the "T-12", with a weight of 19,500 kilograms (43,000 pounds). The B-36 never fired a shot in anger.

* The Americans also developed unorthodox bombs, one of the most significant being the M-69 incendiary. The first Boeing B-29 raids against the Japanese mainland were performed in the fall of 1944, using high altitude daylight precision bombing with high explosive bombs. For various reasons, this strategy proved ineffective, and in the spring of 1945 the Army Air Force moved to low level incendiary bombing at night.

The M-69 firebomb had been developed earlier in the war and proved ideal for the task. The M-69 was a simple, clever weapon. It looked like a length of pipe 50 centimeters (20 inches) long and 7.5 centimeters (3 inches) in diameter, and weighed only 2.3 kilograms (6.2 pounds). Since handling such a small weapon was inconvenient, and dropping quantities of small bombs from high altitude was wildly inaccurate, it was designed to be incorporated into an "aimable cluster", a type of finned cluster bomb that contained two bundles of 19 M-69s stacked back to back, for a total of 38 firebombs. Incidentally, there were smaller clusters for the M-69 and also cluster configurations for thermate incendiary sticks.

The aimable cluster was fitted with a nose shroud and tail assembly. It was dropped from high altitude and then broke apart at about 900 meters (2,000 feet), scattering its M-69s. Each M-69 then ejected a long strip of cloth to stabilize itself, and crashed nose-first into buildings below. On impact, it ignited its payload of napalm, which shot out of the tail of the bomb in a burning jet. Under optimum conditions, this jet could travel 45 meters (150 feet). The M-69 was small and could not penetrate the roofs of solidly constructed buildings. However, most Japanese buildings were lightly built and extremely vulnerable to fire. A copy of a Japanese residential area was built in the US to test the M-69, and was incinerated in a test bombing.

The low level fire-bombing raids began in March 1945, starting with a devastating attack on Tokyo that killed over 80,000 people and left a million homeless. Following raids incinerated Nagoya, Osaka, Kobe, and then worked their way down to the smaller cities. By the time the Americans dropped atomic bombs on Hiroshima and Nagasaki in August, most of Japan's major cities had already been destroyed by the M-69.

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[1.3] MODERN UNGUIDED BOMBS

* World War II unitary bombs were not very streamlined and were poorly optimized for use as external stores as aircraft flew faster and faster. In the late 1940s, the US Navy began to study more aerodynamic bombs, with the research congealing in the development of munitions by Douglas Aircraft for their little A-4 Skyhawk strike aircraft in the 1950s. The result was the Mark 80 series of "Low Drag General Purpose (LDGP)" bombs. These munitions, known as "slick bombs" (as opposed to the older "fat bombs"), are spindle-shaped munitions, filled with about 50% explosive by weight. There are four variants:

Mark 82 & M-117 slick bombs

While the US Air Force adopted the Mark 80 series, the service also had unique requirements, and developed two bombs of their own:

This family of weapons is referred to as the "common six", and has been widely adopted by US allies, many of which, for example South Korea and Israel, build the bombs under license.

Although in their standard configuration these bombs are fitted with a "slick" tail with four fins, a popout-fin tail is often fitted to the 225 kilogram Mark 82, making it a "Snakeye", and to the 340 kilogram M-117, in which form it is referred to as the "M117R", "M117 Snakeye", or "Retarder". Snakeyes were very widely used in the Vietnam war.

M-82 Snakeyes

Popout-fin tail sections have been replaced by ballute tail sections, more formally referred to as "Air Inflatable Retarding (AIR)" tails. AIR tails have been devised for the Mark 82, 83, and 84 bombs. The first use of such weapons was during the US air strikes on Libya in 1986 designated Operation EL DORADO CANYON.

Other nations of course have their own series of unitary bombs. The British still specialize in penetrating bombs, though most of their modern munitions are much smaller than the Grand Slam, in the 450 kilogram (1,000 pound) range. The French Societe des Atelier Mecaniques de Pont-Sur-Sambre (SAMP) organization manufactures GP bombs in a range of sizes from 50 to 400 kilograms (110 to 880 pounds), along with appropriate tail and nose kits.

The Soviets developed a series of GP bombs under the general designation "FAB", with specific designations giving the size in kilograms: "FAB-50", "FAB-100", "FAB-250", "FAB-500", and so on. There appear to be at least two series of FAB bombs, one resembling US WWII fat bombs except with a ring tail instead of a box tail, and a more streamlined series that resembles British bombs, though with the same ring airfoil. The Soviets also developed the "RBK" fragmentation bombs, such as the "RBK-250" and "RBK-500". In addition, the Soviets developed a penetrating bomb, the "BetAB-500", plus a rocket-boosted penetrator bomb, the "BetAB-500ShP".

* The Americans developed their own penetrating bombs, first the 900 kilogram (2,000 pound) "BLU-109/B" and then the 2,250 kilogram (5,000 pound) "BLU-113/B". Both are about is 75% hardened steel casing by weight. The BLU-133/B has since been replaced by the externally similar "BLU-122/B", which has a superhard casing made of an alloy known as "Eglin steel". These bombs are used as building blocks for constructing guided "smart" bombs, discussed later. By the way, "BLU" stands for "Bomb Live Unit"; dummy training bombs received the designation of "BDU" for "Bomb Dummy Unit" or, more informally, "Bomb Dead Unit".

The US military never fielded their own runway breaker muntion, but did obtain the French Matra "Durandal" 205 kilogram (450 pound) runway-cratering weapon, known in US service as the "BLU-107/B". The USAF purchased thousands of Durandals. The Durandal weighs about 195 kilograms (430 pounds) and is parachute-retarded after low-level drop. Once it achieves a nose-down attitude, it fires a rocket booster that slams it into the ground, where it explodes and blasts out the runway. It can penetrate up to 40 centimeters (16 inches) of concrete, and leaves a crater with an area of about 200 square meters (2,150 square feet). USAF F-111s could carry up to 12 of these weapons at a time, while French Mirage 2000s could handle a total of 8.

BLU-107 Durandals on F-111

* The Americans also developed very large high explosive bombs, such as the unusual 6.8 tonne (15,000 pound) "BLU-82/B" bomb, which was 80% explosive by weight. This bomb was unusually filled with a "gelled slurry explosive (GSX)", a mix of ammonium nitrate, aluminum powder, and liquid gelling agent, instead of conventional military high explosives. The reasons for using GSX, normally a mining and earth-moving explosive, in the BLU-82/B are unclear, but may be due to cost and for safety in handling, since the slurry was mixed from materials that are easy to handle and poured into the bomb before use. GSX could be stored for some time after being mixed, but it became increasingly unstable, making it inappropriate for more general military use. Some sources claimed the BLU-82/B is a fuel-air explosive weapon, but a mudlike slurry would hardly make a very good aerosol.

A BLU-82/B was fitted with a 1.2 meter (4 foot) daisy cutter fuze and rolled out of the back of a C-130 Hercules transport, to descend to earth under a parachute while the aircraft left the area as quickly as possible.

BLU-82/B being loaded for airdrop

The munition was not designed as a weapon as such. It was developed during the Vietnam War as a combat engineering tool in "Commando Vault" operations to clear helicopter landing zones in jungles, blowing down trees and vegetation without leaving a crater. It appears to have been a bit more bark than bite, but the bark was really awesome.

The first use of the BLU-82/B was in Vietnam in 1970, and they were used several more times in that conflict. Eleven BLU-82/Bs were dropped during the Gulf War, apparently to clear minefields and for psychological effect. The blast effect of the BLU-82/B was compared to the effect of a giant hand sweeping over the desert for kilometers around. They had a terrible effect on the morale of Iraqi troops, and drops of these large bombs were often accompanied by leaflets stating that more of them were coming.

At least three more BLU-82/Bs were dropped during the Afghanistan campaign in 2001. During that conflict the news media referred to the BLU-82/B as the "Daisy Cutter" bomb, though of course that name could be applied to any bomb of any size with a daisy cutter fuze; the BLU-82/B was better known as the "Big BLU". It was occasionally called the "Commando Vault" as well, but strictly speaking that only defined a jungle-clearing operation.

BLU-82/B detonation

The military depleted their stockpile of BLU-82/Bs in Afghanistan, with the last expended in 2008. By that time a new heavy munition, the "Massive Ordnance Air Blast (MOAB)" munition had been developed, and is discussed later since it is a guided glide bomb.

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[1.4] A VERY BRIEF HISTORY OF UNGUIDED ROCKETS

* The origins of airborne rockets for ground attack are obscure, but their first major use was in World War II. Most of the major combatants developed unguided rockets for use with attack aircraft, and these weapons had devastating effect on armor and other targets. The simplicity and effectiveness of unguided rockets have kept them in use to the current day.

The Soviets were one of the first combatants to develop airborne rockets, introducing the "RS-82" rocket even before the Nazi invasion in the summer of 1941. The RS-82 had a diameter of 8.2 centimeters (3.23 inches) and was highly effective. Later it the war, the RS-82 was followed by a similar but bigger rocket, the "RS-132" (with, naturally, a diameter of 13.2 centimeters / 5.2 inches). Both types of rockets were built with either a blast-fragmentation warhead for attacking soft targets or a hollow-charge warhead for attacking armor.

Soviet RS-82 unguided rockets

The earliest unguided rocket system used operationally by the United States in World War II was the "M-8" 11.4 centimeter (4.5 inch) triple-tube "Bazooka" launcher. This weapon consisted of what looked like three pipes bundled together, each containing a stubby rocket about 40 centimeters (16 inches) long, with the bundle attached to an aircraft's stores pylons in place of a bomb. The M-8 had fins that unfolded in the airstream after launch. It was very inaccurate, but had a reasonable punch. The M-8 was used with US Army Air Force aircraft such as the Republic P-47 Thunderbolt, North American P-51 Mustang, and Lockheed P-38 Lightning.

The British developed their own unguided airborne "rocket projectile (RP)". This was a simple weapon with fixed cruciform tailfins and a tubular body 7.62 centimeters (3 inches) in diameter. The RP was originally developed for barrage anti-aircraft fire in the desperate days of 1940:41, but after the threat of invasion receded, the large stocks available were adapted for use by attack aircraft. The RP could be fitted with an 11 kilogram (25 pound) solid armor-piercing head, or a bulbous 12.5 centimeter (5 inch) high explosive warhead. The high-explosive version was also known as the "60 pounder" (27 kilogram) RP for the warhead weight. These rockets were used to arm the Hawker Hurricane, Hawker Typhoon, Bristol Beaufighter, de Havilland Mosquito, and other aircraft.

The relatively cluttered launch rails used by the RP usually reduced the speed of the carrier aircraft by a good fraction, but the rockets were effective enough to make the reduction in performance worthwhile. The Typhoon so was devastating in attacks on German armor with the 60-pounder that it became known as "Rockoon".

5-inch FFARs being loaded on F4U Corsair

The RP was also supplied to some US aircraft such as the Grumman TBM Avenger, but the US Navy decided to develop their own equivalent, which emerged in 1943 as the "Forward Firing Air Rocket (FFAR)". The FFAR had a diameter of 8.89 centimeters (3.5 inches), a length of 1.4 meters (4 feet 7 inches), and a solid steel warhead for attacking naval targets, primarily submarines. It was also produced with a warhead derived from a 12.7 centimeter (5 inch) artillery shell, this variant being known as the "5-Inch FFAR".

However, that was too much warhead for too little rocket, so a rocket with a diameter of 12.7 centimeters was developed to mate to the warhead. The result, the "High Velocity Air Rocket (HVAR)", was introduced in mid-1944. The HVAR was also occasionally known as "Holy Moses" because of its impressive destructive effect -- "Holy Moses!" being a popular exclamation at the time. The HVAR was 1.83 meters (6 feet) long and weighed 63.5 kilograms (140 pounds). It had fixed fins and was carried on streamlined stub pylons under the wings of aircraft such as the Thunderbolt, Mustang, Grumman F6F Hellcat, and Vought F4U Corsair.

HVARs on A-26

The HVAR had either a general-purpose explosive warhead, or a steel-cased warhead that could penetrate 3.8 centimeters (1.5 inches) of armor or 1.2 meters (4 feet) of reinforced concrete. It was also used in the Korean War with good effect. Some photographs from that time show HVARs fitted with large conical armor-piercing "RAM" warheads. These were apparently improvised when UN forces found out just how hard a target Soviet-built tanks could be; the RAM HVARs were quickly phased out when improved HVAR warheads were developed.

After developing the HVAR, the Caltech research group then developed a bigger unguided rocket named "Tiny Tim". The Tiny Tim resembled a scaled-up HVAR, had a diameter of 30 centimeters (a foot), a length of 3.12 meters (10 feet 3 inches), and a weight of 582 kilograms (1,284 pounds) including a 270 kilogram (590 pound) warhead. It was carried on standard bomb racks, igniting after it had fallen free of the aircraft. The Tiny Tim was intended for "bunker busting" and other hard targets. It was deployed on US Navy Hellcat fighters late in the war in the Pacific, and also used with A-1 Skyraiders and other aircraft during the Korean war.

Republic F-84 with HVARs & Tiny Tims

* The Germans were impressed by rocket-firing Allied fighter-bombers and decided to develop their own unguided air-to-ground rockets, with very little result. The first attempt was to use the "Panzerschreck" infantry anti-tank rocket, a scaled-up derivative of the American "Bazooka" rocket, from underwing launch tubes. Trials showed the Panzerschreck didn't have enough range, and so it was followed by the "Panzerblitz I", which took the hollow-charge warhead from the Panzerschreck and fitted it with an improved rocket motor. It was launched from underwing wooden "crate"-style racks.

The Panzerblitz I still wasn't satisfactory, and so the next step was to adapt the "R4M" rocket. The R4M was a fairly potent weapon that was used in some numbers at the end of the war for air-to-air combat. It had a diameter of 5.5 centimeters (2.17 inches), was kept on course with pop-open fins, and was fired from underwing racks. The R4M was modified for ground attack by fitting it with a hollow-charge warhead, creating the "Panzerblitz II".

* The R4M was used as the basis for unguided rockets built by many nations after the war. Instead of mounting individual rockets individually on a stores pylon, unguided rockets were fitted to aircraft in "pods" that could be streamlined and could carry a large quantity of folding-fin rockets. In some cases, pods were built as the forward sections of external tanks.

Since such unguided rockets are very simple and easy to manufacture, they are widely available in many different versions. In 1948, the US introduced a 70 millimeter (2.75 inch) "Folding Fin Air Rocket (FFAR)" -- recycling the acronym for the older Forward Firing Air Rocket. The 2.75 inch FFAR, also once known as "Mighty Mouse", was derived from the German R4M; it was fired in clusters by 1950s interceptors such as the Northrop F-89 Scorpion, North American F-86D Sabre, and Lockheed F-94C Starfire to knock out Soviet bomber formations attacking the North American continent.

The FFAR saw little or no action in air-to-air combat, which was fortunate because most pilots who fired them in tests found them much too inaccurate. It was used for ground attack in the Vietnam War with good effect. It was standard armament for attack helicopters like the Bell AH-1 Hueycobra, and was often carried by fixed-wing close-support aircraft such as the A-1 Skyraider, fitted with different versions of cylindrical pods accommodating 7 or 19 rockets. The FFAR was often fitted with a smoke warhead for target marking by forward air controller aircraft.

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[1.5] MODERN UNGUIDED ROCKETS

* The old FFAR survives, and indeed remains in widespread use, in a slightly improved form as the standard "70 millimeter" rocket. 70 millimeter rockets are essentially simple munitions and made by a variety of vendors. Improvements have been added over the decades, such as the ability to "spin up" within the launch pod to ensure greater accuracy, more powerful motors, and most noticeably the replacement of the old folding fins with wraparound fins.

70 millimeter rocket launcher

The most common 70 millimeter rocket is the "Hydra 70" series. US Army gunship helicopters use the 7-tube M260 launcher and the 19-tube M261 launcher. US Navy aircraft use the 7-tube LAU-68D/A and 19-tube LAU-61C/A launchers. The launchers are reusable and have an ablative cooking to slow down "cook off" of the munitions in a fire.

The current Hydra-70 Mark 66 rocket motor is 106 centimeters (3 feet 6 inches) long and weighs 6.16 kilograms (13.6 pounds), when not fitted with a warhead. It burns for about 400 meters (1,300 feet) before burnout, giving the rocket a range of over 10 kilometers (6.2 miles) when launched at altitude. The range of the earlier Mark 40 rocket motor was only 8 kilometers (5 miles).

The Mark 66 has four nozzles that are slightly canted to set the rocket spinning at a rate of about 10 revolutions per second, improving the weapon's stability and accuracy. The Mark 66 has a wraparound, spring loaded tailfin assembly. Warheads are screwed into the front of the motor; the rocket can be fitted with general-purpose blast-fragmentation, submunition, flechette, smoke, and illumination warheads.

Hydra-70 warheads

* The US Navy and Marine Corps -- though not the Army or Air Force -- also use a larger 12.7 centimeter (5 inch) rocket, known as the "Zuni", in ground attacks during the Vietnam War, carried in a four-round pod. The Zuni was developed in the early 1950s to replace the HVAR. Early Zunis used the "Mark 16" motor and pop-out fins, while later production used the "Mark 71" motor and wraparound fins. The Zuni remains in service; it can be fitted with high-explosive, anti-armor, flare, smoke, chaff, and practice warheads.

The Zuni is usually carried in an LAU-10 four-round launcher. Although there is a version of the LAU-10 with an ablative coating, out of safety concerns the Navy withdrew the Zuni from carrier operations in the late 1980s, though it was retained for ground-based operations. More recently the Navy relaxed the carrier ban to allow the Zunis to be carried by sea-borne special operations helicopters.

Zuni packs & Bullpup ASM on F-8E Crusader

* The most popular European unguided rockets are the old 68 millimeter (2.68 inch) SNEB, and the improved Thomson-Brandt Armaments (TBA) 68 millimeter and 100 millimeter rockets. Warhead options for the current TBA rockets include blast-fragmentation, hollow-charge anti-armor, illumination, smoke, chaff, penetrating demolition, and an interesting series of anti-armor warheads containing a number of large penetrating darts.

Bofors of Sweden has also produced a range of unguided rockets, with diameters of 60 millimeters (2.4 inches and used generally for training), 75 millimeters (2.95 inches), 135 millimeters (5.3 inches), and 180 millimeters (7.1 inches). It is unclear if all these rockets are still in production.

The Soviets were particularly enthusiastic about unguided rockets, and produced them in a wide range of sizes. The smallest is the 57 millimeter "S-5" folding-fin rocket. It was introduced in the 1950s, has been manufactured in massive numbers, and is still in production. It is fired from eight-tube, 16-tube, or 32-tube launchers. The 57 millimeter rocket, incidentally, has often been used as a "man-portable" weapon by insurgents in nations that obtained stocks of Soviet hardware such as Iraq, Libya, and Syria. Insurgents homebrewed their own launch systems for the rockets, using pipes and other available materials; Iraqi insurgents even made one four-round launcher that an insurgent fighter perched on his head, with pistol grips to fire the rockets and a plexiglass face shield.

The 80 millimeter "S-8" and 122 millimeter "S-13" rockets were developed in the late 1970s. The S-8 is fired from a 20-round launcher, while the S-13, which is designed for runway cratering and attacking "hardened" targets, is fired from a five-round launcher. The Soviets built a huge 240 millimeter (9.5 inch) unguided rocket, reminiscent of the US Tiny Tim. Sources also mention 160 millimeter and 212 millimeter unguided rockets, but it seems they were not built in large quantities.

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