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[2.0] US Smart Bombs In The 21st Century

v1.0.0 / chapter 2 of 2 / 01 nov 16 / greg goebel

* US development of guided munitions has continued into the 21st century, with diversification into smaller and bigger weapons, with smarter guidance systems. Smart bomb technology has also been applied to cluster munitions, existed unguided rockets, and artillery shells.

GBU-39/B SDBs


[2.1] SDB, MOAB, & MOP
[2.2] AGM-154 JSOW
[2.3] MINIATURE GUIDED BOMBS
[2.4] OTHER US SMART MUNITIONS
[2.5] COMMENTS, SOURCES, & REVISION HISTORY

[2.1] SDB, MOAB, & MOP

* The US Air Force has acquired a particular interest in a lightweight GPS-guided bomb, known as the "GBU-39/B Small Diameter Bomb (SDB)", initially known as the "Small Bomb System (SBS)" -- which in turn was a follow-on to a proof-of-concept effort, the "Miniaturized Munitions Technology Demonstration (MMTD)" program.

The SDB is a penetrating bomb, with a weight of about 110 kilograms (250 pounds), and length of about two meters (6 feet 6 inches). It has the same penetrating capability as a heavyweight penetrating weapon, able to punch through 90 centimeters (3 feet) of reinforced concrete, but only has a load of 17 kilograms (38 pounds) of explosive. The SDB was primarily designed for carriage on new stealthy piloted and unpiloted strike aircraft to allow them to carry weapons internally, while still giving them enough firepower to destroy a number of separate targets in a single sortie. Of course, it can be carried externally, with four SDBs carried on a single multiple ejector rack, replacing a single JDAM; an F-15E Strike Eagle can carry 12 SDBs, all independently targetable. The SDB is also a good store for drones like the General Atomics Reaper.

Early on, the SDB was not envisioned as having wings, but a "Diamondback Swing Wing Adapter Kit (SWAK)", with pop-out wings, was incorporated as standard, allowing the weapon to be dropped from from standoff ranges of up to 45 kilometers (28 miles) at altitude. If the SDB is launched at a hard target, the wing is discarded in midcourse to allow the bomb to build up velocity before striking the target. For soft targets, the wing is retained until the bomb is in range of small arms fire.

The SDB incorporates a "differential" GPS guidance system to provide a smaller CEP, and an improved penetrating structure to allow the weapon to pierce up to almost two meters of concrete. Compact "lattice fins", AKA "grid fins' -- a Russian invention, originally designed for Russian missiles and space launch vehicles, like paddles facing the airstream and with a honeycomb structure to prove a large airfoil area in a compact configuration -- have been considered to assist with internal carriage.

The SDB is fitted with the new "Hard Target Smart Fuze (HTSF)". The HTSF is a fuze mounted in the tail that incorporates accelerometers and a processor chip. The HSTF can determine if the bomb has struck earth, concrete, rock, or empty space; can count the number of layers it has penetrated; and can compute distance or time to determine the appropriate detonation time for a specific target.

SDB strike

The small size of the SDB is also intended to limit collateral damage to nearby civilian structures, and in fact in 2008, Boeing began shipment of a derivative named the "Focused Lethality Munition (FLM)" with a composite case and a new explosive filler to produce blast without fragmentation effects, the concept being to destroy a specific target while minimizing damage to the target's surroundings.

Weapons designers are also now working on a "Multiple Event Fuze" that could trigger multiple munitions functions, such as igniting a blast-fragmentation warhead to tear open an installation, followed by a fuel-air charge to incinerate it. They have developed a laser seeker for the SDB as well, this SDB variant going into service with Special Operations Command in 2014; and a seeker that can home in on a GPS jammer, though that seems to have been purely experimental.

* The Air Force is very enthusiastic about the SDB. Lockheed Martin and Boeing were selected as finalists, with Boeing winning the award in 2003. The first "all-up" test of live weapons was in late 2004, with two being dropped by an F-15E and both successfully striking their targets. Low-rate production and operational introduction began in 2006, with the munition in combat in Iraq before the year was out. The Air Force plans to obtain an initial stockpile of 44,000 SDBs. The weapon was approved for export to Israel in September 2008, seeing initial combat action against Hamas targets in Gaza at the end of the year. It is being license-built in Italy for use by the AMI, the Italian Air Force; the Royal Australian Air Force ordered a batch in 2016.

Boeing has been working with SAAB of Sweden to use an M26 rocket booster and an adapter to launch the SDB from a Multiple Launch Rocket System (MLRS) ground vehicle. M26 rockets were originally built with cluster warheads; the US has not agreed to a ban on cluster munitions, but is de-emphasizing them, with the M26 cluster munition warheads being decommissioned. That leaves a stockpile of rocket motors for other use.

GLSDB

The "Ground-Launched SDB" is clearly an improvisation, but it seems a very effective one, and likely low-cost, given the off-the-shelf availability of its primary elements. It has a maximum range of 150 kilometers (95 miles); it is capable of maneuvering as per a flight program to attack targets from a roundabout direction, if at expense of range. The GLSDB has completed trials, and is being demonstrated to potential customers.

* As a follow-on to the initial SBD, the Pentagon is now obtaining a much smarter "GBU-53/B SDB-2", with more properly integrated airframe; GPS-INS midcourse guidance; a multi-function warhead that can destroy either hard or soft targets; and most significantly, a triple-mode smart seeker -- featuring millimeter-wave radar, uncooled infrared imaging, and laser homing technology. Although Boeing was favored to win the follow-on contract, Raytheon got the award in 2010, with initial low-rate production in 2015. There has been some thought, if no action yet, of an SDB-2 variant with a small turbojet engine.

SDB-2

* At the other end of the size scale is the "GBU-43/B Massive Ordnance Air Blast (MOAB)" GPS-guided bomb, intended for attacking caves and similar hard targets. MOAB was developed on a crash basis for use in the US invasion of Iraq in the spring of 2003, but it reached field units too late to see any use in that conflict. Concept studies began in April 2002, with development beginning in September, and the first drop 42 days later.

It's a huge weapon, with a weight of 9.84 tonnes (21,700 pounds), 8.48 tonnes (18,700 pounds) of that being explosive. It has two long stub wings and four pop-out lattice-fin tailfins, and is activated by twin nose-mounted fuzes. Its GPS-INS guidance, using a GPS receiver on the tail, allows it to maneuver down narrow valleys, where cave hideouts are often sited to complicate air attack, to impact directly on a cave entrance. The massive shock wave propagates down the tunnel, causing destruction by sheer overpressure deep inside.

MOAB bomb

The MOAB acronym is sometimes said to stand for "Mother Of All Bombs". When the MOAB bomb was announced to the public the town of Moab, Utah, protested against the name, but to no effect. MOAB is intended for drop by a C-130s, with the guided glide capability allowing the drop aircraft to stand off from the target area. Only a small batch of MOABs was built, the Air Force seeing MOAB as more or less a prototype of a series of munitions.

The next member of the family, the "Massive Ordnance Penetrator (MOP)", was developed by Boeing. It is a thick-cased weapon with GPS-INS guidance, stub wings, and lattice tailfins, but with a smaller form-factor for carriage on the B-52 and B-2 bombers. It has a length of 6.35 meters (20 feet 6 inches), a diameter of 80 centimeters (31.5 inches), and a weight of 13.6 tonnes (30,000 pounds), about a sixth of that being explosive filling. When dropped from altitude, it can penetrate 60 meters (200 feet) into the ground and still punch through a reinforced-concrete roof. Initial deliveries were in 2012, the program having been accelerated due to worries about Iran's nuclear weapons development program, which is built around a distributed network of underground complexes.

BACK_TO_TOP

[2.2] AGM-154 JSOW

* While the JDAM and SDB projects have provided the US military with a degree of short-range stand-off attack capability, other programs have worked on weapons to attack targets at greater ranges. One of the most important of these, the US Navy and Air Force "AGM-154 Joint Stand Off Weapon (JSOW)" is in extensive service, and has been used in combat.

The JSOW project was initiated in 1986 under the initial name of "Advanced Interdiction Weapon System (AIWS)", the goals being a lightweight, low-cost, fire-&-forget weapon with medium range and the capability to carry different types of warloads. A development contract was awarded to Texas Instruments in 1992. Texas Instruments was later acquired by Raytheon. Initial tests of JSOW began in 1994.

AGM-154 JSOW

JSOW is an unpowered glide bomb, with pop-out switchblade wings and a GPS-INS navigation system. The weapon is smart enough to fly a pre-planned path to its target, making turns and hiding behind mountains. If the proper preplanned launch point cannot be reached, the pilot can release it and, as long as the target is within a pie-slice wedge on the cockpit display, let the weapon determine its own flight plan. JSOW is light enough to be carried by smaller attack aircraft such as the F/A-18, the F-16, or AV-8B Harrier.


   AGM-154A JSOW:
   _____________________   _________________   _______________________
 
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                2.7 meters          8 feet 11 inches
   length                  4 meters            13 feet
   total weight            475 kilograms       1,050 pounds
   speed                   subsonic glide weapon
   range at altitude       75 kilometers       47 MI / 40 NMI
   _____________________   _________________   _______________________

The first version of JSOW to be developed was the "AGM-154A" or "JSOW-A", which entered full-scale production in 1999. The AGM-154A carries 145 BLU-97A/B Combined Effects Munitions (CEM) for use on "soft" targets.

The BLU-97A/B is a can-shaped submunition with a weight of 1.54 kilograms (3.4 pounds), built around a hollow charge that can penetrate up to about 18 centimeters (7.1 inches) of armor. Once dispensed, the CEM pops out a number of small "spider" tail tabs to ensure that it falls nose-down, and then deploys a ballute -- balloon-parachute -- to retard its fall. It has a scored case that blasts into 300 fragments, as well as an incendiary zirconium ring. When the JSOW-A makes its final attack dive on a target, it blows off covers on either side of its boxy fuselage, and a gas-inflated aluminum bladder scatters the CEMs out the sides.

JSOW was introduced to combat in January 1999, during air strikes by US Navy aircraft on Iraqi air-defense sites, and was used in later combat actions. The results of these strikes exceeded expectations, and the US Air Force accelerated its efforts to get JSOW into full service. Some of the strikes demonstrated that JSOW wasn't able to correct for wind drift as well as desired, but Raytheon implemented software fixes to correct the problem. A "Block II" variant, with improved resistance to GPS jamming, was introduced in 2017. A multiple ejector rack has been developed to allow carriage of two JSOWs, or other weapons of similar size, on a single stores pylon.

AGM-154 JSOW

* Both the US Air Force and the Navy considered an anti-armor version of the JSOW, the "AGM-154B" or "JSOW-B", with six BLU-108/B Sensor-Fuzed Weapon submunitions -- discussed below -- but it was canceled. The US Navy has acquired a variant with a unitary warhead, the "AGM-154C", or "JSOW-C" featuring a British-developed two-stage "Broach" penetrating warhead. The JSOW-B also features an imaging infrared seeker and datalink, compatible with the existing pylon-mounted control pod developed for the Navy Walleye glide bomb, to allow precision strikes on a target. The seeker, inherited from the SLAM-ER cruise missile, is capable of autonomous operation for fire-&-forget attacks.

Low-rate production of the AGM-154C began in the summer of 2003, with operational introduction in 2005 on the F/A-18 Hornet. Improvements have been phased into production, such as a simplified and refined airframe and a new anti-jam GPS unit. A "JSOW-C1" subvariant with an infrared seeker capable of attacking mobile maritime targets, and a two-way Link-16 datalink performed its first free flight test in 2011, with introduction to service in 2016.

A number of nations have obtained JSOW, including Australia, Canada, Finland, Greece, Netherlands, Poland, Saudi Arabia, Singapore, Turkey, and the UAE. Raytheon has developed a low-cost JSOW with using a Mark 82 lightweight unitary warhead, with this variant designated the "AGM-154A-1" and intended for the export market.

A version of JSOW powered by a Williams International WJ-24 turbojet and named the "Griffin-36" was offered for the British Conventionally Armed Standoff Missile (CASOM) competition in 1996, but was not selected. Raytheon flight-tested an extended range "JSOW-ER" in 2009, fitted with a Hamilton Sundstrand TJ150 small turbojet, with the weapon achieving a range of 480 kilometers (300 miles / 260 NMI); the baseline JSOW design actually included space for an engine. There has been no commitment to production.

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[2.3] MINIATURE GUIDED BOMBS

* There has been a push towards very small smart munitions. The US Army and Northrop Grumman developed a small smart submunition, the "Brilliant Anti-armor Munition (BAT)", which was a 20-kilogram (44-pound) weapon looked like a cylinder about 1.5 meters (5 feet) long with a bulbous head when stored in its dispensing system. When released, the BAT popped out four wrap-around tailfins and four long, straight cruciform gliding wings around the midbody. The bulbous nose was fitted with an infrared sensor, and the wingtips were fitted with long spikes fitted with acoustic sensors.

Once deployed, the BAT glided to a preprogrammed target location, with a cluster of BATs dispersing to ensure that they didn't attack the same targets, and used the acoustic sensors to identify the general location of a tank. Once a target was boxed by the acoustic sensors, the infrared sensor took over, directing the BAT to hit the target directly from the top, destroying it with a two-stage penetrating warhead. An Improved BAT (IBAT), with a combined millimeter-wave radar / infrared imager seeker, was also developed.

The plan was to deploy the BAT on the Block II version of the Army Tactical Missile System (ATACMS or "Attack 'Ems"), updated to carry a warload of 13 BATs. However, the Block II ATACMS was canceled in 2003, and BAT went into limbo. A smart weapon that could smash enemy armor concentrations was no longer a particularly relevant weapon for the "dirty little wars" the Army was suffering through by that time; it might have been a nice thing to have, but other weapons were needed at the time.

* The irony was that a simplified BAT ended up being a perfectly useful weapon. It was straightforward to mate a laser seeker to the BAT airframe, and in the spring of 2003, the Army performed a demonstration of a laser-guided BAT named "Viper Strike". The weapons were test-dropped from a US Army Hunter drone, scoring seven hits out of nine drops.

The lightweight, accurate Viper Strike seemed like an ideal weapon for drones, themselves good weapons for dirty little wars, and quickly went into service as the "GBU-44/B", with the Hunter apparently the initial carriage platform. The munition was handled and carried in a bomblike canister with tailfins that ejected the Viper Strike after drop.

The BAT smart submunition didn't turn out to be what was needed at the time, but the Viper Strike proved a handy little glide bomb. Viper Strike was intended for high-precision "top down" attacks on targets, particularly in urban or other built-up areas where collateral damage is a concern. Some Viper Strikes have been modified from such stockpiles of BATs as were accumulated before that program went on hold, with these weapons retaining the wingtip probes for the BAT acoustic sensors, but the probes have been deleted from new-build GBU-44/Bs.

Strike platforms can carry a fair load of such small munitions, providing the ability to plaster a small target area with little collateral damage. The reach of the Viper Strike also enhances its capability: it has a glide ratio of 10:1, meaning that it only falls one meter for every ten meters of horizontal flight, and so a drop from a mere kilometer of altitude gives the munition an attack "footprint" with a radius of up to ten kilometers.

MBDA acquired the Viper Strike from Northrop Grumman in 2011. A backup GPS-INS navigation system has been developed by MBDA to permit midcourse guidance for long-range drops, laser guidance being troublesome when the target is very far away; improved software has also made the munition more effective against moving targets. This version of the weapon is referred to as the "GBU-44/E Viper-E".

It has been since updated to "Viper-E II", with GPS-INS guidance only, and a datalink to permit midcourse updates for attacking mobile targets. There have been mentions of other possible updates, such as a fragmentation belt for the shaped-charged warhead to add anti-personnel effects, and a mode to disable the warhead, turning the munition into a "smart rock" -- 20 kilograms moving at hundreds of kilometers an hour can make a strong but selective impression on an unarmored target.

The Viper Strike can be carried directly on a stores pylon, but it is also handled in and launched from a "Common Launch Tube (CLT)". CLTs can be loaded up for dispensing from the rear ramp of a C-130 using a 10-tube "Gunslinger" launcher, which precludes pressurization of the C-130's cargo bay; or a two-tube "Derringer door" launcher, with two such weapons dropped from chutes built into a crew door, permitting pressurization to be maintained. There's talk of fitting the Derringer door into the Bell-Boeing MV-22 Osprey tilt-rotor aircraft.

* MBDA also developed another small glide bomb, the "Small Air Bomb With Extended Range (SABER)", featuring a switchblade-type wing system; GPS-INS midcourse guidance; a laser terminal seeker, with other seeker options possible down the road; and a rocket-boost capability for standoff range. It is available in configurations from 4.5 kilograms (10 pounds) to 13.6 kilograms (30 pounds).

Lockheed Martin did not fail to notice the interest expressed in the Viper Strike, and has developed their own little smart bomb, the "Small Smart Weapon" AKA "Scorpion". It has a weight of about 16 kilograms (35 pounds), four pop-out tailfins, and a straight pivoting wing. The default seeker system is semi-active laser, but the Scorpion is designed to support swap-in seeker modules based on other technology, such as millimeter wave, imaging infrared, or thermal infrared.

Lockheed Martin Scorpion small smart bomb

Lockheed Martin has designed a carrier that can accommodate three Scorpions on a Hellfire missile launch rail, with the interface protocols emulating the Hellfire's. The Scorpion's form-factor is similar to that of the LUU-series parachute flares, and so the little bombs can be carried in a four-tube SUU-25 pylon-mounted flare dispenser, with two bombs per tube for a total warload of eight bombs.

Raytheon has developed their own small smart bomb named "Pyros" -- initially the "Small Tactical Munition (STM)" -- with a weight of 6 kilograms (13.5 pounds), with a GPS-INS midcourse navigation system and laser seeker. It is unclear if anyone has bought SABER, Scorpion, or Pyros.

* However, Raytheon has been delivering another small smart munition, the "AGM-176 Griffin", in quantity, and it has seen operational service. It has a weight of 20 kilograms (44 pounds), including handling launch tube; a length of 1.1 meters (43 inches); and a 5.9-kilogram (13-pound) warhead. It features a laser seeker, but also has GPS-INS guidance; it has a programmable fuze, along with cruciform pop-out fins on the tail and midbody. It is not a glide bomb as such, having a solid-fuel rocket motor.

Griffin sea launch

There are two production versions of the Griffin, the "Griffin A" and "Griffin Block II / B":

Production began in 2008, with over 2,000 delivered by early 2014; it appears to be the US small smart munition of choice, particularly by Special Operations Command. A "Block III" enhancement of the Griffin B has been introduced that features the ability to hit targets on the move; it also features a new laser seeker, and a new combined-effects warhead. Raytheon has worked on a "Griffin C" with an imaging infrared seeker along with the laser seeker and a and datalink, as well as a "Griffin C-ER" with a larger rocket motor for much longer range, but there have been no buyers just yet.

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[2.4] OTHER US SMART MUNITIONS

* The US has also developed other smart munitions, such as cluster bombs, laser-guided 70-millimeter rockets, and artillery shells.

The USAF fielded a series of cluster-munition dispensers under the family name of "Tactical Munitions Dispenser (TMD)". All are almost identical in appearance, being 2.34 meters (7 feet 2 inches) long and 41 centimeters (16 inches) in diameter, with three panels that are popped off to disperse the submunitions; The detail differences between them are to accommodate different sorts of submunition loads. Different TMDs with different weapons loads each have their own designations, for example:

The first of the "smart" TMDs, the "CBU-97/B", wasn't really a guided weapon itself, but carried ten "BLU-108/B Sensor-Fuzed Weapon (SFW)" submunitions, each in turn with four "Skeet" anti-armor submunitions featuring infra-red seekers.

The SFW was an outgrowth of work on smart weapons by Textron Defense Systems beginning in the mid-1980s under the ASSAULT BREAKER effort. Development of such systems was accelerated by the defense cutbacks in the 1990s that required the military to obtain "force multipliers" to make best use of restricted resources. Trials of the SFW began in the early 1990s and demonstrated the lethality of the weapon. In a test conducted in late 1991, for example, an F-16 dropped four canisters from low altitude, which then dispersed a total of 40 BLU-108/B submunitions over a column of 24 vehicles. 17 hits were scored on 11 of the vehicles.

The CBU-97/B is based on the standard TMD canister, and has a loaded weight of 450 kilograms (1,000 pounds). The CBU-97/B can attack armored vehicles over a wide footprint. The munition can be delivered at altitudes from 60 meters to 6 kilometers (200 to 20,000 feet). An F-16 can carry 4 CBU-97/Bs; an F-15E can carry 10.

CBU-97/B

Once a CBU-97/B dispenser is released, a pyrotechnic charge pops open the TMD's three panels to release the ten BLU-108/B submunitions. Each submunition is a cylinder that is decelerated by a small parachute; the parachute also orients the submunition vertically over the target area. Chute deployment timing is staggered to allow the submunitions to disperse, and the actual area covered is a function of aircraft speed and the timing interval selected.

As the cylinder descends, the four Skeet warheads flip out from the body of the submunition. Each Skeet consists of a 13.3-centimeter (5.25-inch) diameter disk of flat copper backed by an explosive charge that is boresighted to a protruding infrared sensor. Once the cylinder is aligned properly over the target area, the parachute is cut loose as a rocket motor fires through two nozzles, which are canted so that they stop the cylinder's fall and set it spinning. When the cylinder's spin gets up to speed, the Skeets are released in pairs to fly away from the cylinder; they wobble in flight to allow the infrared sensor to scan over the ground below in a spiral pattern.

When a Skeet flies over a vehicle, the warhead's infrared sensor identifies it as a target, and fires the explosive charge. This slams the wadded-up copper plate into the target at about 1,500 KPH (930 MPH), punching through armor and sending splinters through the interior. Explosive reactive armor is ineffective against such a "kinetic kill" projectile. The Skeets are not guided; they are dispersed more or less at random over a target area, and only fire if they spot a target. If the Skeets don't find a target after a certain length of flight, they explode into fragments as a harassment measure and to prevent "pollution" of the landscape by hazardous dud submunitions.

The infrared sensor is capable of working through fog, since it is close to the target; it works at night and through electronic countermeasures. Not all the warheads are expected to find targets, but the dispersal pattern of the 40 Skeets carried by an SFW is expected to be effective against concentrated targets such as an armor column.

Although SFW development proved more troublesome than expected, the SFW did enter service, proving highly effective. It was introduced to combat during air strikes during the Kosovo campaign in 1999, with SFW-loaded CBUs acquiring the nickname of "cans of whup-ass".

The latest SFW configuration includes seeker improvements to permit attacks on naval vessels and even parked, cool aircraft and ground vehicles. The explosively-formed projectile scheme has been modified and enhanced, and a highly reliable self-destruct system is being considered to reduce collateral damage. The new projectile includes a ring of 16 explosively-formed penetrators around the central main penetrator, providing an additional shotgun effect. In addition, a more insensitive explosive is used to meet Navy requirements for shipboard storage and handling.

* The USAF then developed a guided tailkit for the TMD family. The "Wind Corrected Munitions Dispenser (WCMD)" or "Wick-Mid", provides INS guidance through the addition of a new tailkit assembly. Unguided cluster bomb units have to be released from low altitude to keep them from being blown off target by the wind; adding a guidance system permits such munitions to be dropped from high altitude. The original program definition only envisioned an INS tailkit that could provide a CEP of 26 meters (85 feet), which was regarded as acceptable for a wide-area weapon such as a cluster bomb unit, but the tailkit is designed to accommodate a GPS guidance system should such an upgrade seem necessary. WCMD configurations include:

A WCMD with BLU-114/B submunitions -- which throw out carbon-filament threads to short out power stations as a "soft kill" -- has also been introduced, and the Air Force Research Laboratory has developed an "agent defeat" weapon based on the WCMD named "Stop" to allow it to attack chemical or biological weapon storage facilities using 3,800 titanium flechettes to puncture storage tanks and production facilities. Two of these weapons, designated "CBU-107/B", were expended in the invasion of Iraq in the spring of 2003 under the name of "Passive Area Weapon (PAW)".

WCMDs on F-16

The weapon been used in combat, with CBU-103/B munitions used in the Afghanistan campaign in the winter of 2001:2002. The United Arab Emirates has purchased a number of the weapons. The Air Force experimented with the "WCMD-ER", which had popout gliding wings to give it a typical range of about 55 kilometers (30 nautical miles) and was fitted with a GPS-guidance upgrade. However, it was canceled in 2006 due to technical difficulties and budget cuts.

* After World War II, along with the "slick" bomb family, the US military also acquired unguided rockets in their arsenal, the best-known being the 70-millimeter unguided rocket, the most heavily produced type being the "Hydra-70".

The Hydra-70 is generally fired from 7-tube and 19-tube launchers. 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 -- possibly the number of different heads led to the "Hydra-70" name.

Given the modular nature of the Hydra-70 and the emergence of laser-guidance systems, it was a natural progression to develop a laser-guidance kit for the Hydra-70 -- though oddly, it didn't happen until the 21st century, presumably because it was regarded as too small to be worth it. The Army and General Dynamics worked on a laser-guided Hydra-70 system, designated the "Advanced Precision Kill Weapon System (APKWS)", nicknamed "Hellfire JR" after the Hellfire laser-guided anti-tank missile. The program suffered from "requirements creep", and was canceled after suffering from poor test results.

The Army scaled back requirements, and ran a second competition for the APKWS, with BAE Systems winning the contract. Initial all-up tests were in 2007. The APKWS amounts to a module, the "WGBU-59/B", that's screwed between the warhead and rocket motor of a standard Hydra-70 rocket, with the module providing guidance using four pop-out fins directed by a "distributed aperture semi-active laser seeker (DASALS)". The baseline rocket configuration uses the standard M151 HE warhead for the Hydra-70.

APKWS

A sensor, or "eyeball", for the DASALS is mounted on each of the four pop-out fins, instead of the nose -- a nose-mounted sensor wouldn't be practical, given the installation. There are little control surfaces on the ends of each of the four pop-out wings. Before launch, the wings are sealed inside the seeker module, only popping out after a half-second following launch; this helps prevent damage to the seeker from the launch of another rocket in the launch pod. The seeker, which has a 40-degree field of view, then acquires the target, remaining on lock by balancing the inputs from the four "eyeballs".

BAE Systems says the APKWS costs about 15% as much as a Hellfire, though the low cost is partly due to the large existing stockpile of Hydra-70 rockets -- all of which are easily converted to a guided configuration with the APKWS. It does require an updated "Digital Rocket Launcher (DRL)" that includes the appropriate interface connections for the "smart" weapons.

The US military is very enthusiastic about APKWS, the effort becoming a multiservice program, with the US Navy taking charge to get the weapon into service -- likely because the Army was so heavily committed in Iraq at the time. The APKWS entered low-rate production in 2011, and was fielded in 2012, with initial deployment on US Marine Cobra helicopters in Afghanistan, the weapon also going into Navy inventory. It has proved very reliable and highly lethal.

While the APKWS can't inflict much damage on heavy armor and hardened targets, its low cost and small blast radius would be a particularly handy weapon for the sort of dirty little wars currently in fashion. It can be carried by any platform that can carry the Hydra-70, with little crew training; laser designation can be provided by ground forces or other platforms if the launch platform doesn't have the capability. Its light weight also makes it an excellent weapon for small drones.

* APKWS isn't the only effort to build a guided 70-millimeter rocket. Lockheed Martin lost out on the competition for APKWS II, but went ahead on development of their "Direct Attack Guided Rocket (DAGR)" weapon anyway. DAGR has been successfully test-fired. Unlike APKWS, DAGR features a nose-mounted seeker, derived from the Hellfire anti-armor missile; it is unclear if the nose-mounted configuration limits compatibility with standard 70-millimeter rocket warheads. Lockheed Martin has developed a four-pack launcher that can replace a single Hellfire on a standard Hellfire launch rack, and has also conducted trials for ground launch.

DAGR ground launch

Lockheed Martin has also introduced a 5-kilogram (11-pound) laser-guided glide bomb named the "Shadow Hawk" -- with a diameter of 70-millimeters, suggesting it was derived from DAGR. It is intended for carriage on small drones. Several other guided weapons based on the 70-millimeter rocket have been developed, but their operational status is unclear.

* While the US Air Force focused on the 70-millimeter rocket, the US Navy and Marines focused on the more potent 127-millimeter (5-inch) "Zuni" rocket, which saw extensive use in Vietnam and later wars. It features a solid-rocket motor 1.95 meters (6 feet 5 inches) long, with four pop-out tailfins. Like the Hydra-70, it has modular warheads, including high-explosive, anti-armor, flare, smoke, chaff, and practice warheads.

That modularity suggests the possibility of a laser-guidance kit for the Zuni as well. Matra BAE Dynamics Alenia (MBDA) test-fired a Zuni with a laser seeker in 2009; BAE Systems also says that it would be straightforward to modify the APKWS seeker to the Zuni. So far, it doesn't seem anyone's adopted a "smart" Zuni, though it would be a fairly potent weapon, able to take out light armored vehicles.

* As laser guidance systems were developed for bombs, it seems obvious that they should be developed for artillery as well; in fact, as mentioned earlier, the design studies that led to the Paveway LGB started out as investigations into laser-guided artillery rounds. Following these studies, in the early 1970s the US Army initiated development of the "Cannon-Launched Guided Projectile (CLGP)" -- better known as the "M712 Copperhead".

Copperhead is a laser-guided artillery round for launch from 155-millimeter (6.1 inch) guns. Martin Marietta conducted studies for the CLGP in the late 1970s, leading to a production contract in 1979. However, full development of a smart munition that could be fired out of an artillery piece, subjecting it to roughly 10,000 gees of acceleration, proved difficult, and Copperhead didn't enter service until the mid-1980s. It was used in both Iraq Wars.

Copperhead Strike

Copperhead is 1.37 meters (4 feet 6 inches) long, of course is 155 millimeters in diameter, and weighs 62.4 kilograms (137.5 pounds). Maximum range is 16 kilometers (10 miles). It is fired like a conventional artillery round, and requires little special handling or training -- though there are switches on the munition to specify trajectory and laser designation options.

On firing, a thermal battery and a timer inside the Copperhead are activated, a gyro is spun up, tailfins pop open, and the laser seeker begins to scan. The seeker acquires laser reflections from a target as the munition falls toward the earth, and then fins pop open from the midbody to guide the Copperhead into its target, which is destroyed by the shell's hollow charge warhead. Work was performed on a Copperhead variant with a radar-homing seeker, but this version did not go into production.

The US Army worked with Aerojet to develop a 155-millimeter round with "smart" submunitions under the designation of "M898 Sense And Destroy Armor (SADARM)". SADARM consists of two submunitions in a 155-millimeter shell. As the shell descends into the target area after launch, it ejects the two submunitions, which then release a ballute to stabilize themselves, and finally release parachutes to slow their descent. Each submunition carries an infrared and a millimeter-wave sensor, and as the submunition descends it scans the area below it for the signature of an armored vehicle. On targeting an armored vehicle, the submunition fires an explosively-formed projectile into the thin-skinned top of the vehicle. SADARM went into production in 1996. Over a hundred were expended during the US invasion of Iraq in 2003, with the munition being judged more effective than expected.

* From the 1990s, the US military's infatuation with GPS led to introduction of GPS-guided artillery shells. Raytheon has developed the "Excalibur / M982" 155-millimeter munition for the US Army. Raytheon worked on the program with assistance from Bofors of Sweden, a BAE Systems subsidiary.

The munition has a pop-out tail and nose fins for guidance, and was designed with a 20-meter (66-foot) CEP. Excalibur has a secondary seeker mode to home in on GPS jammer transmissions, providing aggressive anti-jamming capability. Initial firing of an "all-up" round was in June 2002, with the Army introducing the M982 into service in Iraq on a combat evaluation in 2006. The munition proved all that was expected of it, with a CEP of 4 meters (13 feet) 92% of the time. Raytheon introduced a new variant of the munition in 2013 that added a laser terminal guidance seeker.

M982 Excalibur

The Army also worked with BAE Systems and Alliance Technical Systems (ATK) to develop the "Precision Guidance Kit (PGK)" to convert ordinary "dumb" shells into GPS-guided shells. The PGK is a "smart fuze" that can replaces standard 105-millimeter and 155-millimeter shell fuzes, with the fuze mounting fins to provide guidance. Initial test firings were in 2008 and initial operational fielding of the "XM1156" was in 2013. PGK is regarded as "cheap and dirty" complement to the Excalibur, not a replacement for it.

Other smart artillery rounds are in the works. Work on another GPS-guided rocket-boosted shell, originally named the "Long Range Land Attack Projectile (LRLAP)", began with a collaboration of BAE Systems and Lockheed Martin; it later evolved into the "Multi-Service Standard Guided Projectile (MS-SGP)" program, to develop 5-inch and 155-millimeter guided munitions for the US Navy, Marines, and Army. The first "all up" test of MS-SGP was in 2013; maximum range is expected to be almost 100 kilometers (60 miles), with a 5 meter (16.4 foot) CEP.

* There's also been work on smart mortar rounds. The US Army has sponsored development by ATK of a smart round for the 120-millimeter mortar, with the designation "M395 Precision Guided Mortar Munition (PGMM)", in the form of a hollow-charge gliding munition with popout fins and GPS guidance. The program has been protracted, but the PGMM saw operational use in Afghanistan from 2012. In that same year, the US Marines awarded a contract to Raytheon to build a "Precision Extended Range Munition (PERM)" round for the USMC's 120-millimeter mortar. Details were unclear; Raytheon partnered with Israel Military Industries for the program.

81-millimeter mortar round with RCFC

General Dynamics has tested a "roll controlled fixed canard (RCFC)" fuze that can be screwed into 81-millimeter mortar rounds in place of a traditional fuze, providing them with GPS-INS guidance using moving fins on the fuze body. At the outset, the RCFC fuze was defined for use of mortar rounds as an air-dropped munition, the small size of the mortar round making it appropriate for small drones. There is the minor disadvantage that mortar rounds aren't designed for airdrop -- they don't have lugs -- requiring the development of a clamp-type drone stores carriage system. It seems the RCFC has also been tested for standard mortar launch, but so far it doesn't seem anyone has bought it.

The US Navy has been working on a more sophisticated guided 81-millimeter mortar round under the "Advanced Capability Extended Range Mortar (ACERM)" program. Tests have demonstrated a range of 22.6 kilometers (14 miles) -- a doubling of range -- with a 10-meter (33-foot) circular error probability (CEP). The round is programmed using a ruggedized tablet computer.

While a rocket booster was considered to obtain the longer range, rockets are relatively expensive and have handling issues. The solution was to add two pop-out wings to add glide distance, with two forward-mounted canard fins providing control. The ACERM uses GPS for midcourse navigation, and a laser seeker for terminal attack.

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[2.5] COMMENTS, SOURCES, & REVISION HISTORY

* This document started life in 1999 as what would become a comprehensive survey of global smart munitions. In 2014, I realized it had become very awkward and un-maintainable, and axed it. I have since been extracting and updating elements of it for more selective documents.

GBU-20/B Planar Wing Weapon

* As concerns copyrights and permissions for this document, all illustrations and images credited to me are public domain. I reserve all rights to my writings. However, if anyone does want to make use of my writings, just contact me, and we can chat about it. I'm lenient in giving permissions, usually on the basis of being properly credited.

* Sources for this document include:

* Revision history:

   v1.0.0 / 01 nov 16
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