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[1.0] Dumb Bombs (1): Unitary Bombs

v3.0.0 / chapter 1 of 10 / 01 apr 12 / greg goebel / public domain

* Although smart munitions are coming into vastly wider use, the unguided dumb bomb remains a major weapon. Dumb bombs are cheap, and when used by sophisticated strike aircraft, highly effective. They also come in a bewildering variety of forms, optimized for different missions, and can be used as a basis for smart munitions. This chapter and the next provide an overview of dumb bomb technology.

US WWII 4,000 pound GP bomb


[1.1] BASICS OF DUMB BOMBS
[1.2] A SHORT HISTORY OF DUMB BOMBS
[1.3] UNITARY EXPLOSIVE BOMBS

[1.1] BASICS OF DUMB BOMBS

* Aerial dumb bombs, as noted, 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, and illumination and marking flares. There are also 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:

New "smart" fuzes with digital processors and sensors are 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.

* 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 SHORT HISTORY OF DUMB 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. The US developed a 1.95 tonne (4,300 pound) bomb named the "Mark 1" in the early 1920s, but abandoned the weapon because the Army had no airplanes big enough to carry it. There was also a belief that the Mark 1 was simply more bomb than any target would ever need.

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 German Luftwaffe was oriented toward tactical warfare, rather than strategic bombing, and its primary high explosive bombs were the 50 kilogram (110 pound) "SC-50" and 250 kilogram (550 pound) "SC-250" bombs. Larger HE bombs, including the 500 kilogram (1,100 pound) "SC-500" and 1 tonne (2,200 pound) "SC-1000", were developed, and carried by larger bombers. A 1.4 tonne (3,000 pound) armor-piercing bomb, the "PC-1400" was developed, as well as a 1.8 tonne (4,000 pound) bomb, the "SD-1800".

One of the most significant Luftwaffe tactical munitions was the small 2 kilogram (4.4 pound) "SD-2" antipersonnel fragmentation bomb, known as the "butterfly bomb". This weapon looked like a small can with a curved cover over one side. On release, the cover popped open, deploying two linked circular fins from the ends of the bomb and connected to the bomb by a short cable. The fins spun to slow the fall of the bomb. Interestingly, the US used an exact copy of the SD-2 butterfly bomb during the Korean war, under the designation "Mark 83".

butterfly bomb

Another important tactical weapon was the 4 kilogram (8.8 pound) "SD-4" hollow-charge antitank munition. The SD-2 and SD-4 could be carried on racks or in cluster bomb canisters, such as the "AB-250" 250 kilogram canister, which split into halves on release to scatter its "splitterbombe (submunition)" payload. The AB-250 could carry 144 SD-2s or 30 SD-4s. It could also accommodate 224 tiny "SD-1" munitions, 17 "SD-10" bombs, 184 "B-1" incendiaries, or 116 "B-2" steel-nosed incendiaries. A bigger "AB-500" 500 kilogram canister was also used.

* At the beginning of the war, the British relied on stockpiles of antiquated "General Purpose (GP)" bombs, which were mostly small, and were so old that they often failed to explode. As the RAF ramped up its war against the Germans, better bombs were developed. The British fielded two classes of HE bombs, "Medium Capacity (MC)" and "High Capacity (HC)".

MC bombs were of traditional configuration, of moderate size (such as 225 kilograms / 500 pounds), and used for tactical targets. The HC bombs were much larger, in sizes of 0.9, 1.8, 3.6, and 5.4 tonnes (2,000, 4,000, 8,000, and 12,000 pounds). The HC types were thin skinned, generally lacked tailfins, and resembled large 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 weapons 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

British incendiary bombs were generally either 1.8 kilogram (4 pound) thermite sticks, or the ingenious 11.3 kilogram (25 pound) incendiary bomb. This weapon descended by parachute, blew off its tail on landing, and then ejected seven firepots at intervals over a total of ten minutes. The bomb casing itself had a thermite charge that was ignited when the firepots were expended. The British also developed large incendiary bombs, in weights of 113 and 250 kilograms (250 and 500 pounds) that were tanks of gasoline with a rubber thickener. Apparently there were even larger incendiaries in this configuration that were used for target marking.

* The British developed highly specialized bombs for certain missions. The most famous of these was the "Upkeep" bouncing bomb, used for the attacks performed by the elite Royal Air Force (RAF) 617 Squadron on the Moehne, Eder, and Sorpe dams on the night of 16:17 May 1943. The Upkeep weapon was designed by Dr. Barnes Wallis, who had been trained as a structural engineer but turned to aircraft and weapons engineering, becoming well known for his geodetic-framed Vickers Wellington bomber.

Upkeep was really a kind of depth charge, and its operation reflected Wallis's knowledge of structures and their vulnerabilities. It was designed as a 4.2 tonne (9,250 pound) drum, and was carried underneath a modified Lancaster heavy bomber. The bomb was given a 500 RPM backspin before it was released at low altitude over the surface of the water, in front of a dam. It would then skip over the water, run into the surface of the dam, roll down its face, and explode at a predetermined depth. Confinement of the explosion to the face of the dam by water pressure multiplied the effect of the blast.

The bombs breached the Moehne and Eder dams. The actual military usefulness of this action is still debated, but the Upkeep weapon worked precisely as designed, even though nothing like it had been done before. Wallis had hoped to build his bomb as a dimpled sphere, something like a giant golfball, which would have been more aerodynamically efficient than a drum. A tight schedule meant that he had to settle for the drum. However, a smaller spherical golfball style munition was also built. The 270 kilogram (600 pound) "Highball" bomb was designed to be dropped by Mosquito bombers against naval targets, but development of this weapon proved troublesome and it was never used in combat.

The Germans tried to develop a spherical bomb of their own, the 385 kilogram (850 pound) "Kurt" bomb, in response to the Upkeep attacks. This weapon was to be boosted by a rocket to provide some standoff distance to protect the launch aircraft. The project was abandoned in 1944.

* While Wallis's bouncing bombs were something of a dead end, he also developed the first serious penetrating bombs. 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 such a "Deep Penetration (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. Grand Slam was so massive that it required special heavy duty handling even when empty.

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 used their own series of GP bombs during the war, resembling pills with box fins. US GP bombs used early in the war included:

   bomb       metric             english
   ______     ________________   ______________

   M-30          45 kilograms      100 pounds
   M-31         135 kilograms      300 pounds
   M-34         225 kilograms      500 pounds
   M-44         450 kilograms    1,000 pounds
   M-34         900 kilograms    2,000 pounds  
   ______     ________________   ______________

Later in the war, this series was replaced by improved GP bombs:

   bomb       metric             english
   ______     ________________   ______________

   M-57         113 kilograms      250 pounds
   M-64         225 kilograms      500 pounds
   M-65         450 kilograms    1,000 pounds
   M-66         900 kilograms    2,000 pounds  
   ______     ________________   ______________


World War 2 fat bombs

The US developed a 1,815 kilogram (4,000 pound) GP bomb, but it is unclear if it saw much or any service. The Americans found that even the biggest GP bombs were almost completely ineffective against hard targets, and so towards the end of the war they developed the "Disney" rocket-boosted hard target bomb, with a weight of 2,040 kilograms (4,500 pounds). It was initially used in March 1945 in attacks on submarine pens. The US also had a range of small fragmentation and metal-incendiary bombs. Napalm was used late in the war, with drop tanks fitted with fuzes serving as casings.

* The US Army's Fifth Air Force, under General George Kenney, demonstrated a particular flair for imaginative tactical use of existing aerial bombs. While prewar Army philosophy envisioned using high altitude bombers to perform attacks on enemy naval vessels, in practice hitting even a large ship from high altitude was very difficult.

Kenney's bomber pilots, operating with Douglas A-20s and North American B-25s, developed an ingenious tactic known as "skip bombing" to attack Japanese ships. The aircraft flew in at low altitude and released a bomb so that it would "skip" over the wavetops and slam into the side of the ship. The bomb was fitted with a delay fuze to ensure that the bomber was clear before the explosion occurred. The tactic was very dangerous, with incautious bomber pilots striking the masts of their targets or even being downed by their own bombs, bouncing back up from the sea.

Kenney's pilots also made effective use of parachute-retarded 10 kilogram (23 pound) fragmentation bombs, or "parafrags", in attacks on Japanese airfields in New Guinea. Strikes were made in two waves, with the first wave of bombers fitted with nose machine guns to suppress Japanese antiaircraft artillery, followed by a second wave that released swarms of parafrags to shred enemy aircraft sitting on the ground. Phosphorus incendiary bombs were then dropped to complete the destruction.

parafrags against the Japanese

* The most devastating conventional bomb used by the Americans, however, was 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.

* The US Army Air Force 509th Bomb Group, which performed America's two nuclear strikes on Japanese cities with B-29s, also dropped a very specialized conventional bomb, known as a "pumpkin". This was an egg-shaped 4,080 kilogram (10,000 pound) conventional HE bomb in the shape of the "Fat Man" fission weapon dropped on Hiroshima. The pumpkins were used for operational training up to the actual atomic strikes, with 37 of them dropped on targets in Japan.

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[1.3] UNITARY EXPLOSIVE 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 generally 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.

* Since general purpose bombs are a fairly straightforward technology, indigenous designs are manufactured and used by many countries, sometimes alongside American Mark 80 designs. The British, for example, have a series of GP bombs of their own design.

After their experience with the big Barnes Wallis bombs in WWII, the British still possess considerable expertise in penetrating bombs, though most of their modern munitions are much smaller, in the 450 kilogram (1,000 pound) range. Various marks of such bombs are available, and they can be fitted with either "slick" or retarding tail units. Some are believed to produce enhanced seismic shockwaves to create "earthquakes" that can crack extremely hard buried targets, but details are unclear.

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. SAMP also produces copies of US Mark 80-series and other US bombs.

The French Navy needed insensitive munitions for shipboard use, with Matra BAE Dynamics Associated (MBDA) and the French state-run Societe Nationale des Poudres et Explosifs (SNPE) producing blast-fragmentation weapons in sizes of 125 kilogram (275 pound) and 250 kilograms (550 pounds). These bombs are known by the designation of "Bombe Aeronvale de Nouvelle Generation / Corps de Bombe a Effets Multiples Securise (BANG/CBEMS)", meaning "New Generation Naval Aviation Bomb / Multiple Effects Insensitive Bomb Body". The two types of weapon are of course known as the "BANG 150" and "BANG 250". The BANG bombs first saw service with French forces policing Afghanistan.

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". Details of Soviet-Russian weapons still remain scarce in the West, though more information is becoming available.

* 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 Americans also developed some 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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