Counter-rocket, artillery and mortar
Counter-rocket, artillery and mortar (C-RAM) is the U.S. Army term for a new defensive technique that detects and destroys enemy projectiles in flight. C-RAM complements older counterbattery techniques that destroy the firing site, which may not be practical if the enemy is firing from a populated area. It is a new mission for the Air Defense Artillery (ADA) branch. ADA continues to have separate systems of surface-to-air missiles against aircraft and ballistic missile defense systems against short-range ballistic missiles.
While the U.S. has operational C-RAM in Iraq and Afghanistan, and at the highly realistic Joint Readiness Training Center, Israel is actively developing C-RAM to protect urban areas, which it sees as a having different constraints than the U.S. military system, and announced a successful operational test in March 2009;  Iron Dome may be deployed by the end of 2009. 
Previous "counter-artillery" systems, such as the AN/TPQ-36, tracked a shell back to its point of origin, but relied on counterbattery methods to prevent the next attack: counterbattery gives the coordinates to one's own artillery, which fires on the enemy point of origin attempting to destroy the weapons there. Counterartillery sensors only detect, and counterbattery is preemptive deadly force. C-RAM, instead, is active defense: it intercepts and destroys the rocket, artillery shell, or mortar shell in midair. the C-RAM system proper does not attack the point of origin.
A concept of "seven pillars" was drawn up by a 2004 NATO new working group dubbed "Defence Against Mortar Attacks" (DAMA). Made up of representatives from NATO member states directly concerned (e.g. the US, Germany, the Netherlands, Spain, Canada, France, Great Britain, Greece and Denmark). The pillars are:
- command and control
Only four of those pillars are truly part of "active defense", which is what differentiates C-RAM from counterartillery detection & warning, counterbattery, and passive protection. The U.S.Army provides more detail the pillars, but not all of the "pillars" are truly active defenses: 
|Active defense||Preemptive||Passive defense|
|Command and control direct active defense, passive defense and response||Respond "application of lethal fires before or after RAM attacks"||shape "actions taken to deny the enemy's use of tactically advantageous terrain or to channel enemy forces into areas where they can be observed."|
|sense||protect:actions taken to harden sites or disperse assets to mitigate the effects of RAM attacks.|
|warn (cue C-RAM interceptor)||warn threatened troops to take cover; friendly aircraft to stay out of engagement volume|
There is an Army C-RAM official website. Cite error: Invalid
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Counterbattery methods are inappropriate for situations where the threat is from guerrillas firing unguided rockets or mortars from urban areas. Rockets, in such situations, may be launched from single-use launchers fired by a timer, so there is no equipment to destroy. More importantly, even if there were a mortar, counterbattery into an urban area would be apt to cause unacceptable civilian casualties. If the counterbattery weapon used antipersonnel or "dual-purpose" cluster submunitions, the percentage of submunitions that do not detonate, but still are dangerous, effectively creates an antipersonnel minefield. There is a international initiative to ban antipersonnel mines, so such methods become even more unattractive.
While there are anti-ballistic missiles and surface-to-air missiles, they are designed to engage much larger targets than artillery, light rockets, and mortars; a typical mortar shell is 81mm in diameter and approximately 240mm long. Katyusha and GRAD rockets, as well as locally made variants, are larger, on the order of 150mm diameter and 2 meter length.
Mortar shells have successfully been shot down at Balad Air Base in Iraq. One article from mid-2008, without explicitly naming systems, speaks of knocking down the 100th enemy round.
Command and control
For the U.S., the Forward Area Air Defense (FAAD) is considered the core of the initial C-RAM systems. FAAD interfaces with multiple sensors and information feeds in the Air Defense Artillery cell at Brigade Combat Team level.
Several U.S. systems provide C-RAM sensing, starting with the AN/TPQ-46 Light-Weight Counter-Mortar Radar, which gives short-range but 360 degree coverage. AN/TPQ-36 and AN/TPQ-37 radars have, respectively, medium and long range, but are directional.
While not all the details have been released, it is likely that electro-optical sensors give warning; there is an electro-optical tracking as well as radar fire control sensor on the current "Centurion" Land-Based Phalanx Weapon System (LPWS) intercepting autocannon. Another potential sensor is the Unattended Transient Acoustic MASINT Sensor (UTAMS)
There is more than one kind of warning that must be sent out. Obviously, soldiers in the potential impact area need to be directed to take cover. Friendly aircraft also need to know about both the incoming threat projectiles and the fact that C-RAM is about to engage it, so they do not fly into the trajectory of either.
Friendly aircraft are tracked with the AN/MPQ-64 Sentinel radar, which has a good deal of commonality with the AN/TPQ-36. The Sentinel feeds into FAAD.
Early C-RAM sensing and warning were not precise enough to localize the threat to a specific part of a large base. A few harassing rounds could effectively shut down a large base, affecting both on-base functions and the deployed units it supports. With a localized warning, only the soldiers directly threatened need stop their activities. The Wireless Audio Visual Emergency System (WAVES) receives warning from sensors and alerts soldiers threatened by the weapons.
There is very rapid development. Initial systems use 20mm autocannon. A 35mm autocannon and a laser system are in the demonstration phase. Israel is developing a proximity kill missile.
The gun systems present a threat to personnel on the ground. Firing at 180 rounds per seconds, in short bursts, will put a large number of rounds in the air. In the original naval application of Phalanx, solid tungsten shot were used, to have the maximum probability of deflecting a large missile. RAM projectiles need far less force to deflect, or more likely, detonate them in midair. The Centurion system uses high-explosive, self-destructing rounds that are expected to break into sufficiently small pieces such that they are not a threat to people under the engagement area, but this is still to be fully tested. With the larger rocket targets, there may also be substantial pieces of the rocket body that falls to the ground. It remains to be seen if there will be a ground hazard.  Laser systems, of course, will not put any additional objects into the sky, although there is a concern that chemical lasers may produce a localized toxic hazard around the mount.
Gun systems are also large and heavy. It takes 18 hours to emplace the LPWS, and it has a limited area of coverage. Laser systems may have shorter range but still will be of substantial size. This is part of the Israeli justification for using distributing small missile launchers for area coverage.
In use in Iraq and Afghanistan is the Centurion LPWS, a modification of the Phalanx close-in weapons system, a 20mm autocannon originally deployed to protect ships against sea-skimming anti-shipping missiles (ASM). Phalanx was effective against older, subsonic missiles, but is being replaced against the increased threat of high-performance missiles such as the Russian Moskit.
LPWS has two radar and a forward-looking infrared sensor. The first radar, which searches for the target after being cued, is a Ku-band with Moving Target Indicator. The fire control radar is also Ku-band, using pulse Doppler techniques. Phalanx always used two radars: it followed the target with one, and tracked its own stream of shells with the other; its fire control computer moved the gunfire to intercept the target. The FLIR sensor is new; it also has a recorder that allows review of engagements.  Raytheon has proposed adding a coaxial high-energy laser. 
Land warfare RAM, however, while smaller than ASM, are, in some respects, easier to track. They are on a ballistic trajectory that can be predicted, against the clean background of the sky. In contrast, a sea-skimming missile will fly just above the water, taking advantage of the radar clutter of waves, and also often maneuvers just before impact, guiding all the way into the target.
Israel has raised concerns about the existing and near-term systems, which it believes are too optimized for point defense of high-value targets to be useful for its need for urban area protection. There are, however, conflicting reports that Israel is trying to buy Centurion. Alternatives here include both an Israeli wide area guided missile interceptor system called Iron Dome, and some variant of the Northrop Grumman Skyguard laser system. 
Israel continues to improve a multilayered missile defense system that also would have capability against larger, longer-range unguided rockets as well. Such rockets would be engaged by the lower-altitude systems, such as MIM-104 Patriot PAC-3 in the atmosphere, and still would use point defense. THAAD, Arrow-2, and a possible land adaptation of RIM-161 Standard SM-3 would remain focused on ballistic missiles.
Proximity kill missile
Iron Dome uses a missile called Tamir, with autonomous control to have it engage only those incoming Palestinian fired Qasam improvised rocket, Katyusha and other unguided rockets, deployed by Hezbollah, as well as 155mm artillery shells, from points of origin up to 70 km away. Iron Dome target acquisition and threat assessment will use the Elta Advanced Artillery Radar (AAR).
Command and control come from a Battle Management & Weapon Control (BMC), which, after identifying projectiles presenting a threat, will command the best-placed launcher to fire a Tamir. BMC has an uplink to the Tamir and guides into proximity of the target; Tamir is not hit-to-kill as are the gun and laser systems. A constraint of targeting is that the engagement should take place over a neutral area, where there is little to suffer collateral damage, as opposed to avoiding it with self-destructing munitions in Centurion.
A U.S. development system called the Tactical High Energy Laser has demonstrated the ability, since 2000, to shoot down RAM. Funding was stopped in 2006, due to budget cuts and concerns that the range was too short, requiring a larger number of interceptors. Northrop Grumman continued development using internal funds, working on a "relocatable" version of THEL. Its radar is already operational in Israel, providing early warning from Palestinian attacks on the the city of Shderot.
In 2006, Northrop Grumman announced the Skyguard Laser Based Counter-MANPADS/C-RAM System, not to be confused with the Oerlikon-Rheinmetall gun-based system.  Note that it is not only a C-RAM system, but intended to have a role in protecting airfield landings and takeoffs from man-portable air defense systems, or shoulder-fired surface-to-air missiles that are a distinct concern in the civilian air transport industry. It could engage MANPADS targets at a range of roughly 20 kilometers (12.4 miles), but a reduced C-RAM range of 5 kilometers (3.1 miles). In October 2006, Northrop Grumman received a 18-month U.S. Department of Homeland Security contract to evaluate effectiveness against threat to airliners.
- Mitchell, Christopher R. (January-March 2006), "C-RAM Battery: Proposal Would Place Majors in Command of Air Defense Artillery's Counter-Rocket, Artillery and Mortar Batteries", Air & Defense Artillery: 21-23
- United States Joint Forces Command, Joint fires team helps JRTC improve force protection training
- "U.S., Israel Pursue Counter Rocket, Artillery & Mortar(CRAM) Weapons", Defense Update, February 2008
- "Israel: 'Iron Dome' rocket shield test a success", Cable News Network, March 27, 2009
- Barbara Opall-Rome (1 October 2009), "Training under fire: Israel’s Iron Dome blends operational, instructional worlds", Training and Simulation Journal
- Terma, Ground Based Air Defence: Counter Rocket, Artillery & Mortar – for Air and Area Protection
- Oerlikon Contraves & Rheinmetall Defences (November 2006), New challenges for air defence: Skyshield system to thwart terrorist attacks
- Ripley, Tim & Richard Scot (May 30, 2007), "UK deploys Phalanx C-RAM system to protect forces in Iraq", Jane's Defence Weekly
- Rider, Timothy L. (9 May 2008), Countering capability intercepts 100th rocket, mortar in Iraq
- Raytheon (2006), Land-Based Phalanx Weapon System (LPWS)
- Higgins, Tristan S. (academic year 06-07), Roles and Relevance: Army Air and Missile Defense (AMD) in the Post 9/11 World, School of Advanced Military Studies, United States Army Command and, pp. 30-32
- Higgins, p. 27
- Phalanx (CIWS) Block 1B LPWS Testing and Firing (video)
- "Israel seeks U.S. Phalanx system for defense against rocket barrage", World Tribune, 30 July 2008
- "Mobile Tactical High Energy Laser (MTHEL), Northrop Grumman Corporation", Defense Update, July 14, 2006
- "Skyguard Laser Based Counter-MANPADS/C-RAM System, Northrop Grumman", Defense Update, July 14, 2006