Artillery ammunition is designed for use in guns, howitzers, and mortars. Size designations for artillery ammunition range from 37MM through 280MM. Artillery ammunition can be classified according to weapon system (gun, howitzer, mortar), filler composition (explosive or chemical), and military use (practice or service). The diameter, or interior, of a weapon barrel, is designated by the term weapon bore. A weapon bore may be characterized as smooth or rifled. The barrel of a smooth weapon bore, as illustrated at the bottom left, has a relatively flat, smooth surface. The size of the smoothbore weapon is simply its diameter (width of the barrel).
It is generally recognized that the key to the U.S. Army’s efforts to prepare itself for a new era of great power conflict is a new set of long-range fire systems. The most important goals of the precision fires modernization effort are to increase the reach/range at which artillery and rocket systems can engage targets, and to develop new shells and missiles to attack high-value, well-defended targets.
To that end, the Army has a plan to upgrade or modernize its array of artillery, rockets and missile systems. In the near-term, this means enhancing the lethality of existing 155mm howitzers and rocket artillery. But within the next decade, the Army expects to deploy artillery, rockets and missiles that can reach out hundreds, maybe thousands, of miles and accurately strike their targets.
A precision-guided munition (PGM, smart weapon, smart munition, smart bomb) is a guided munition intended to precisely hit a specific target, minimize collateral damage and increase lethality against intended targets. Because the damage effects of explosive weapons decrease with distance due to an inverse cube law, even modest improvements in accuracy (hence reduction in miss distance) enable a target to be attacked with fewer or smaller bombs. Thus, even if some guided bombs miss, fewer air crews are put at risk and the harm to civilians and the amount of collateral damage may be reduced.
Precision Guidance Kit is one that can be fitted onto unguided bombs, or “dumb bombs”, into affordable GPS-guided, all-weather “smart” munitions.
GPS Guidance Kit technology
Artillery ammunition is composed of the following five general components, Projectile, Cartridge case, Fuze, Propelling charge, and Primer. The projectile is the component that is propelled from the weapon towards the intended target. The cartridge case serves as the container for the propelling charge and houses the primer. Cartridge cases can be made of steel, brass, or combustible material. The propelling charge propels the projectile from the weapon and is carefully designed for the particular role of the ammunition. The primer is the initiating component in an item that produces the flame to ignite the propellant.
Precision Guided Munitions (PGMs), and other so-called “smart” weapons, have established themselves as a key military technology against targets whose destruction requires a high degree of precision. Precision strikes depend on accurate navigation throughout the entire course of a missile’s flight. GPS is a key enabling technology for existing and future military precision navigation applications.
PGK contains a Global Positioning System (GPS) guidance kit with fuze functions and an integrated GPS receiver to correct the inherent errors associated with ballistic firing solutions, reducing the number of artillery projectiles required to attack targets. The increase in efficiency that PGK’s capability provides allows operational commanders to engage assigned targets and rapidly achieve desired effects while minimizing collateral damage. PGK provides improved fire support to the maneuver force commander through effectively reducing target delivery error of conventional artillery munitions, and reduces the number of projectiles required to execute a fire mission.
Small aerodynamic fins allow the system to steer the shell on target. Its GPS receiver compares the PGK’s flight pattern to the coordinates of where it should hit, and the fins adjust its path to match where the round will actually impact. A fail safe exists where if the shell does not impact within 150 m (490 ft) of the intended target, it will land but not explode; the PGK “decides” five seconds after launch whether it expects to impact close enough to detonate. This safety feature is expected to give soldiers more confidence when calling in artillery support close to their position.
The PGK fuze weighs 3 lb (1.4 kg), 0.4 kg (1 lb) more than a standard fuze because of the addition of fins and an alternator. The self-contained system does not need a battery since the alternator inside generates power in flight. Not only is the PGK fuze cheaper to produce than whole purpose-built guided artillery shells, its purpose to turn standard shells into more accurate rounds enables the millions of rounds already in inventories to be upgraded, while new smart shells have to be built to create a stockpile.
The Joint Direct Attack Munition (JDAM) is a guidance kit that converts unguided bombs, or “dumb bombs”, into all-weather “smart” munitions. This weapon can be employed in all weather conditions, without any need for ground support. Because it is possible to jam GPS, the guidance package reverts to inertial navigation in the event of GPS signal loss. Inertial navigation is significantly less accurate; the JDAM achieves a published Circular Error Probable (CEP) of 43 ft (13 m) under GPS guidance, but typically only 98 ft (30 m) under inertial guidance (with free fall times of 100 seconds or less)
The guidance kit consists of a specialized antenna and associated RF components needed to connect the antenna to the GPS receiver. These guidance kits must be extremely robust to handle high g-force associated with a gun launch, often 20,000 g’s or more. This market is continuing to expand with development of “smart” howitzer and mortar rounds. Advances in antenna technology are also making GPS more applicable to a wider variety of munitions.
First, specialized passive antennas are capable of providing a fixed shape antenna beam. For example, a fixed beam, forward-null antenna may focus less energy in the direction of a missile’s flight path, or possibly, a reduced level of energy below the missile’s flight path. This design strategy assumes that most jammers will be co-located with the targets they are intended to defend. A fixed null in the jammer direction could provide as much as 15 dB signal suppression.
Active beam-forming antennas may steer even less signal in the direction of strong in-band (jamming) signals. Effectively, a null-steering antenna could provide 30 dB or more attenuation of the unwanted signal. In the case of multiple jamming signals, the adaptive beam forming process becomes more complex, and requires either additional antenna elements or a reduction in suppression performance. Of course, any benefits gained from adaptive beam forming must be balanced against reductions in satellite signal reception due to the dynamically changing antenna radiation pattern.
Given this complicated operating environment, selection of the appropriate antenna is an essential part of the overall system performance optimization. These special GPS antennas may be conformal or embedded antennas. An example is the 2011TF L1/L2 GPS antenna. This antenna was designed and optimized for both supersonic flight and extreme environmental conditions. The 2011TF GPS antenna features dual o-rings to seal the antenna from the elements. The radome is constructed of high grade polymer resin for UV and abrasion resistance, and resistance to all deicing fluids, jet fuels, and standard cleaning solvents.
This antenna has been used by war fighters in combat operations around the world with successful deployment on guidance units for Paveway 2,000 pound bombs. The Paveway II contains an array of two GPS antennas to provide continuous GPS coverage during weapon flyout through impact.
Boeing developed a Laser JDAM (LJDAM) to provide both types of guidance in a single kit. Based on the existing Joint Direct Attack Munition configurations, a laser guidance package is added to a GPS/INS-guided weapon to increase its overall accuracy. Raytheon has developed the Enhanced Paveway family, which adds GPS/INS guidance to their Paveway family of laser-guidance packages. These “hybrid” laser and GPS guided weapons permit the carriage of fewer weapons types, while retaining mission flexibility, because these weapons can be employed equally against moving and fixed targets, or targets of opportunity. For instance, a typical weapons load on an F-16 flying in the Iraq War included a single 2,000-pound (910 kg) JDAM and two 1,000-pound (450 kg) LGBs. With LJDAM, and the new GBU-39 Small Diameter Bomb (SDB), these same aircraft can carry more bombs if necessary, and have the option of satellite or laser guidance for each weapon release.
Militaries race to employ Precision Guidance Kits
Spice (munition) is an Israeli EO/GPS-guided guidance kit for converting air-droppable unguided bombs into precision guided bombs. Spice can be preprogrammed, with up to 100 different targets it may have to engage during a mission. The one target it will actually engage may then be selected, inflight, by an aircrewman.
The HGK guidance kit (HGK), Turkish: Hassas Güdüm Kiti / Precision Guidance Kit), developed by TÜBİTAK-SAGE, is a GPS/INS guidance kit that converts 2,000-pound (910 kg) Mark 84 bombs into smart weapons. It enables precision strike capability in all weather conditions with long range at a dispersion of 20 ft (6 m).
Armement Air-Sol Modulaire (AASM) is a French equivalent to JDAM. AASM comprises a frontal guidance kit and a rear-mounted range extension kit matched to a dumb bomb. The weapon is modular because it can integrate different types of guidance units and different types of bombs. It uses hybrid inertial navigation system (INS) / Global Positioning System (GPS) guidance. Other variants add infrared homing or laser guidance to increase accuracy.
Denel Dynamics Umbani a precision-guided bomb kit manufactured by Denel Dynamics in South Africa. It consists of a number of modules fitted to NATO standard Mk81, Mk82 or Mk83 low drag free-fall bombs to convert them to glide bombs. DRDO Smart Anti-Airfield Weapon is an Indian precision-guided Anti-Airfield Weapon with the range up to 62 mi (100 km) .
Basir is an Iranian artillery fired laser-guided, 155 mm explosive projectile designed to destroy enemy tanks, vehicles and other moving or non-moving targets with high precision. This weapon is similar in function with Russian Kransnopol or American M712 Copperhead. Basir put Iran among the five countries in the world with laser targeting technology.
The US Army is adding to its inventory of precision rounds, such as Excalibur, and providing jam-resistant, precision-guidance kits for 155mm artillery projectiles. Increasingly, guidance kits are being fitted to “dumb,” or unguided bombs, which steer them to the target post launch.
A conventional unguided M549A1 155 mm artillery projectile has a circular error probability (CEP) of 267 m (876 ft) at its maximum range, meaning that half of the rounds can be expected to land within 267 meters of their intended target. This has made unguided artillery dangerous to use in close combat for fear of friendly fire and collateral damage. The M982 Excalibur was fielded as a guided shell that effectively hit within 6 m (20 ft) of a target, but the Army developed the XM1156 as a cheaper alternative. The PGK fuse can be screwed onto existing M549A1 and M795 projectiles, be fired from M109A6 Paladin and M777A2 Howitzer artillery systems, and hits within 50 m (160 ft) of the target at any range.
The Precision Guidance Kit (PGK) has fundamentally transformed artillery fires operations for the US Army and has very quickly become the “weapon of choice” to support theatre operations. Similar to how the Joint Direct Attack Munition (JDAM) Global Positioning System (GPS) guided tail kit enriched precision guidance for the US Air Force, the PGK GPS guided nose-kit has drastically improved indirect fires for the US Army. The PGK, designated M1156, is a Northrop Grumman designed and produced precision guidance system that turned 155mm “M795” and “M549A1”artillery rounds into smart weapons. HGK-84 is a GPS/INS guidance kit that turns existing 2000 lb Mk-84 general purpose bombs and penetrator bombs into air to ground smart bombs.
Now, Army developers with the Army’s Program Executive Office Ammunition at Picatinny Arsenal are taking the technology to a new level by improving upon the range, accuracy and functionality of the weapon. The PGK-M’s highly accurate, lethal capability enables one-shot hits on the target. It requires less ammunition than conventional artillery to complete the mission, saving on costs, and increasing effectiveness, says BAE. Perhaps of greatest importance, the emerging PGK-M shell is engineered such that it can still fire with range and accuracy in a war environment where GPS guidance and navigation technology is compromised or destroyed.
However, GPS signals are also subject to electronic attacks such as jamming by adversaries. Apart from jamming by adversaries, GPS signals are also subject GPS-spoofing attacks whereby a malicious entity generates a GPS-like signal designed to mislead GPS receivers. “Threats to military GPS have evolved and improved at a rapid pace — from a proliferation of small-scale commercial jamming devices that can readily be purchased on eBay to large-scale military anti-access/area-denial (A2/AD) capabilities,” said MAJ Christopher Brown, assistant program manager Dismounted PNT within the Assured PNT program.
Picatinny Arsenal engineers are leading the development of a GPS alternative using image navigation for precision guidance of munitions, under the Armament Research, Development and Engineering Center (ARDEC). Other research partners include Draper Labs, U.S. Army Research Laboratory, Air Force Research Laboratory and the Aviation and Missile Research, Development, and Engineering Center. The enhanced munition can navigate to a desired location, through a reference image used by the technology to reach the target. The PGK-M includes a collection of ad hoc software programmable radio networks, various kinds of wave-relay connectivity technologies and navigational technology.
The next generation PGK-AJ (anti-jam) will contain new technology that modernizes PGK. Additionally, PGK-AJ will provide compatibility with developmental artillery projectiles and platforms to achieve the Long Range Precision Fires Cross Function Team goals of lethality at extended ranges.
NORTHROP GRUMMAN details PGK
Northrop Grumman’s precision guidance kit (PGK) transforms existing 155-millimeter high-explosive artillery projectiles into affordable satellite-guided precision weapons. The low-cost reliable, fuze-sized guidance kit installs in the artillery shell’s fuze well and also provides traditional fuze functions for height-of-burst and point detonation, Northrop Grumman officials say. PGK provides maneuver forces with an organic precision capability that works in all weather conditions, and fills a gap between conventional artillery and smart munitions capabilities. The PGK uses signals from the Global Positioning System (GPS) to guide artillery shells to their targets with accuracy of less than 10 meters.
The M1156 PGK GPS guidance and navigation unit can be fitted to 155mm artillery projectiles with a deep fuze well to get a step change in accuracy – typically well under 30 metres. It replaces conventional artillery fuzes, requires no additional modifications to the 155mm and can have point-detonating and proximity-fuzing options.
The Northrop Grumman engineering team enhanced the design to have a single moving part and self-generated electrical power and programme management drove increased reliability to better than a standard fuse (which is 20X less complex) as well as paved the way for future PGK derivatives. Supply Chain metrics make the above achievements remarkable: 1100+ parts, 360 part types and 68 sources of supply managed.
“This unprecedented reliability avoided costs of $8.2 million for the US Army. Similarly, the accuracy measurements of these LATs have blown away threshold accuracy performance requirements (of 50m) by realizing an amazing sub 10m CEP average,” the company concludes. “The LAT reliability achieved is unparalleled having achieved 98.89% reliability rate vs a 92% requirement. The result: a battery can now fire for first time lethal effects thus allowing them to get in and get out which consequently saves money and more importantly saves lives.”
The PGK is compatible with various 155 mm artillery stockpiles to reduce dispersion. It was demonstrated on German DM111 shells in September 2014 fired from a PzH2000 self-propelled howitzer. From a distance of 27 km (17 mi), 90 percent of the PGK-equipped German shells landed within 5 meters of the target.
Rheinmetall Denel Munition has formalised a ten-year agreement with Northrop Grumman to develop ammunition technology for future artillery operations. The agreement was signed in February 2021 and focuses on precision-guided enhanced range artillery ammunition solutions. The companies will cooperate on realising an enhanced range 155mm artillery round fitted with an integrated M1156 precision guidance kit (PGK). They will also focus on developing a new 155mm projectile featuring an enhanced integrated propulsion system.
The M1156 PGK, which is already operational with several armed forces, is a quick and affordable option that turns existing types of 155mm artillery rounds into smart weapons. When combined with Rheinmetall’s velocity-enhanced long-range projectile (V-LAP) projectile, the M1156 PGK results in a solution that has been proven in numerous combat operations. In 2019, a conventional artillery projectile achieved a 76km range with a non-Nato Joint Ballistics memorandum of understanding (JBMOU)-conforming 52-calibre gun and RDM 155mm projectile. Currently, enhanced range Rheinmetall artillery ammunition from South Africa is used by the armed forces of more than 12 countries.
BAE’S precision Guidance Kits
BAE Systems has successfully demonstrated the ability of its Rokar Silver Bullet precision guidance kit to transform a standard 155mm artillery shell into a highly accurate munition during a live fire test in Israel. The system successfully proved its versatility through firings from a number of artillery guns including the M109 and the K9 barrel and has been proven effective on several types of shells including the M795 and the K307.
The system has in-flight high correction capability that reduces the requirement for an aiming process as its enhanced accuracy greatly increases the ability to hit a target with the first shot fired. The capability facilitates more precise engagement in urban environments, and against protected targets, while minimizing collateral damage.
The US Army’s Defense Ordnance Technology Consortium (DOTC) awarded BAE Systems and General Dynamics Ordnance and Tactical Systems (GD-OTS) Phase 2 contracts for continued development of technologies to enable 155 mm projectiles to perform against a broad spectrum of threats. The Precision Guidance Kit-Modernization (PGK-M) effort is a new application of technology currently in development by the army as a replacement for the fielded 155 mm Precision Guidance Kit (PGK).
PGK-M will provide enhanced performance against a broad spectrum of threats. In addition, PGK-M will be interoperable with the Army’s new long-range artillery projectiles, which are currently in parallel development,” Audra Calloway, spokeswoman for the Army’s Picatinny Arsenal, told Warrior Maven.
BAE Systems is among several vendors currently developing PGK-M with the Army’s Defense Ordnance Technology Consortium. BAE developers say the kits enable munitions to make in-flight course corrections even in GPS-jammed environments. BAE Systems’ Precision Guidance Kit-Modernization (PGK-M) technology will meet current and future anti-jam requirements, and advance on previously successful capabilities developed to improve the reliability of precision-strike functions in GPS-jammed environments, says BAE.
- Improved accuracy against modern threats
- Reduced Circular Error of Probability (CEP)
- Decreased collateral damage
- M795 and M549A1 standard projectiles
- M109A7 self-propelled Howitzers
- M777A2 lightweight towed Howitzers (manufactured by BAE Systems)
- Miscellaneous developmental rounds and firing platforms
The kit combines enhanced Global Positions System (GPS)-based navigation with an innovative, roll-stabilized guidance unit and antenna array. This integrated technology, paired with a proven, variable deflection canard control method, allows for advanced in-flight correction capabilities.
The PGK-M technology is designed to help warfighters complete every mission accurately:
- Precision at longer distances keeps soldiers away from threats
- Improved GPS anti-jam performance
- Enabled technology compatible for GPS restricted environments (semi-active laser, imagers, pseudolites, datalink, etc.)
“Our experience with munitions handling, gun launch shock, interior ballistics, and guidance and fire control uniquely positions us to integrate precision technology into the Army’s artillery platforms,” David Richards, Program Manager, Strategic Growth Initiatives for our Precision Guidance and Sensing Solutions group, BAE Systems, told Warrior Maven in a statement.