Controlling close support to ground forces
Fire support to ground troops becomes increasingly more risky, in terms of fratricide, as the distance between forces decreases. There is no accident that the term "final protective fire" designates the nothing-held-back, preplanned use of all weapons to keep units from being overrun.
Prior to the 20th century, most artillery was direct fire, and the gunners could see where they needed to fire — until the smoke of "black" gunpowder obscured the view. There was limited use of indirect fire, such as naval mortars, which were controlled by flag or light signals from an observer closer to the target. These weapons rarely were for close support, but for attacking fortifications.
Widespread use of indirect fire in the First World War tended to be against previously surveyed targets, with trajectories laboriously computed by hand. "Creeping barrages" were used to put fire ahead of advancing troops, but these generally moved forward based on a predicted rate of troop advance. If friendly troops moved too slowly, the enemy might have time to recover from the bombardment. If friendly troops advanced too quickly, they would be shelled by their own side.
There was limited air support, but WWI aircraft flew low and slow enough that pilots and gunners had a good chance of visual identification. With the faster aircraft of WWII, even with field radios, it was difficult to establish a coordinate system synchronized between the advancing troops, and air or artillery.
By WWII, however, air and artillery specialists, called, respectively, forward air controllers and forward observers accompanied troops, and were able to give better instructions to distant firing platforms.
Precision control of dumb weapons
Even early in the 20th century, artillery direction became more and more scientific, with Canadian troops, at the Battle of Vimy Ridge in the First World War, using techniques surprisingly like modern methods, but without the benefit of computers.
Serious advances in computer support to field artillery started to be implemented in the 1960s, although the projectiles themselves remained unguided. An early U.S. fire control project, the Field Artillery Digital Automatic Computer (FADAC), went into development in 1958, and remained usable into the 1980s.
There was much cooperative work among Australia, Britain, Canada and the United States, who agreed on standards for critical information such as firing tables. A table standard such as QSTAG 220 let a U.S. unit call for Canadian fire support, without needs for translating among different procedures. These standards became NATO-wide. Nevertheless, the performance of computers usable in the field were marginal in the 1960s and 1970s, and artillery units routinely operated a manual backup. Fire control systems of this period included the U.K. Field Artillery Computer Equipment (FACE), introduced in 1969, and the U.S. TACFIRE, which also started deployment in the late sixties.  TACFIRE is being replaced by the Advanced Field Artillery Tactical Data System, which specifically interoperates with U.K., French, Italian and German systems; its message format is a superset of a NATO standard.
Fast, reliable fire direction systems entered service in the 1980s, but still were focused on dumb weapons and their launchers. These systems also had limited ability to accept precise target designation from the field.
The PGM revolution
PGMs, however, have the potential to reduce fratricide while acting as a force multiplier for ground troops. In many cases, the mission of a ground unit is less to attack the enemy with its own weapons, and more to direct heavy weapons onto them. The widespread availability of using PGMs is not limited to aircraft weapons.  Artillery includes an increasing range of PGMs, not just surface-to-surface missiles but also guided shells and helicopter-launched air-to-surface missiles. Support from high-performance aircraft, however, also is better understood and more capable. 
PGMs are no better than their targeting information. Conventional ground forces increasingly are getting better tools to send targeting information to the PGM launcher. Ground combat vehicles and organic helicopters also have sophisticated target designation capability.
While Global Navigation Satellite Systems (e.g., GPS) are known principally for being sources of position information, their role as a precision time reference is just as important, when modern weapons fire must arrive at a specific point at a specific time.
Requesting close support
No longer is precision fire direction the exclusive province of special reconnaissance (SR) teams. With the restructuring of the United States Army, brigade combat teamss have gained an immense amount of intelligence, surveillance, reconnaissance, and target acquisition/target designation capability. fires brigades and aviation brigades both can deliver PGMs beyond those organic to the BCTs. Specifically, the scouts in the Reconnaissance, Surveillance and Target Acquisition Squadron (Brigade Combat Team) have LRAS3 laser designators
SR teams maintain the ability to guide deep strikes. In either case, directing any support relies on one of two basic guidance paradigms:
Beginnings of control of close support
While there was close air support in the First World War, the technology did not exist to have electronic communications with aircraft, and only limited ability to communicate with artillery. In any event, in both World Wars, PGMs appropriate to close support did not exist.
While PGMs in the Vietnam War were primarily for deep strike missions, there was much more coordination of delivery of air-delivered weapons, however, have been evolving significantly since the early days of Vietnam.. SR teams could place portable radar beacons, and both artillery forward observers and air forward air controllers accompanied troops.
With current modern forces, a unit providing overwatch in ground combat maneuver may be as or more likely to call in strikes as deliver fire from its organic weapons. There is more and more of a trend for foot soldiers to be controllers of strikes rather than using their own kinetic weapons.
Fratricide and deconfliction
Fratricide was, and remains, remains a major concern, and all new close support systems have specific measures to help avoid it. In fire support, the aircraft does not just need a position to destroy the target. In CAS operations there will always be friendly troops in near proximity to the enemy. In other words, it is not enough just to lase the target and pass the location to the aircrew. The aircrew needs situational awareness of friendly troops. After a friendly fire incident, however, deficiencies in giving the bomber the precise location of the supported troops became apparent.
Close air support: ever closer
For close air support, the assumption had been that rapidly changing tactical situations, including sudden changes in geometry between friendly forces and the target, GOT was assumed. If the attack was to be guided from the ground, either the target would be directly illuminated with some equivalent way of putting a virtual "hit me here" indication on the target, such as a laser designator. An alternative, although less preferred because it was much more error-prone, was to put a reference point on the ground that told the weapon "hit over there in relation to my position."
The laser offset technique, however, is a modern and accurate version of that "reference point" approach. Using laser offset, a forward air controller or forward observer designates a reference point to which an intelligent weapon flies. Once the weapon senses that point, it turns on its autonomous target seeker and independently finds and attacks the actual target.
Ground-aided precision strike
More precise than the smoke grenade was to place a radio or radar offset beacon near the target, but the SR troops still face the problem of precise angular and distance measurement from the beacon to the target. In the Afghanistan campaign of 2001, a new technique was adopted, only recently believed possible: ground-aided precision strike (GAPS).  To put GAPS in practice, MG Daniel Leaf, USAF Director of Operational Requirements for Air and Space Operations said, in 2002, "If you had offered the B-1 with JDAMs in direct support of ground forces as a solution 10 years ago, I would have laughed heartily because it’s not what we envisioned." The JDAM's principal guidance mechanism is inertial, with a GPS correction option: a GOLIS model.
To assist the bomber in identifying the target, the ground team designating the target could also designate prominent terrain features, against which the aircrew could orient itself. The electro-optical viewing system could produceimages of the post-strike damage. A radar or other electronic beacon, separate from the targeting system, meets the first requirement.
GAPS was still an "open-loop" system in terms of the weapons, navigation and guidance systems. The early Afghanistan attempts still required voice coordination to give the bomber the coordinates of the target, and there was no automated cross-check that these did not set up incidents of fratricide. . This lack of verification led to one "friendly fire" incident, which killed three Special Forces soldiers and wounded 19 others. A controller had been using a hand-held GPS receiver, whose battery failed. On replacing the battery, the unit reinitialized to show the controller's own position, not the offset from it he had been targeting. He passed the coordinates to a B-52 crew, who had no way of knowing it was the wrong position. They entered it as given, and the JDAM flew accurately and unfortunately onto its own controller's position.
Needs for real-time deconfliction
It could have been avoided if someone, on the bomber, on a command & control aircraft, or at an operations center, had full awareness of the situation. Situational awareness, in this case, means having positive confirmation of several key data:
- Positions, and movement if any, of any friendly forces and civilians in the area
- Positions, and movement if any, of the target
- Means by which the TACP identified the target and the precision of those means, and positive verification of the TACP's identity
- A means of communicating with the TACP, and with the bomber if another center is controlling the attack
- Location, course, and speed of all aircraft that could deliver the requested attack
- Nature of the weapon requested, including its delivery precision
Accurate situational awareness also requires minimizing human error in data entry. Inputting errors are fallibilities that can be removed from the system. US Air Force Chief of Staff John P. Jumper said data is best fed directly into a weapon and then merely confirmed by the human in the loop. Manual data entry, particularly in the cockpit, should be avoided wherever possible
"CAS and GAPS operations do not care what color of airpower is delivering the weapons. Certain segments of the USAF wanted to break out the use of heavy bombers and term it “bomber CAS. However, at the joint CAS symposium held at Eglin, the Navy and Marine Corps were successful in not letting the Air Force call this by a different name.
"If heavy bombers are supporting ground troops in the traditional CAS role, then a name change for that aspect is not needed. [What is being discussed, however, is a new mission:] "Precision firepower called in by TACPs on the ground [is] GAPS and [needs its own doctrine]. The situation in Afghanistan was unique; there was not a large-standing opposing army that was conducting maneuvers to bring firepower to bear against our forces... Airpower was the maneuvering element that was supported by the small fire support teams on the ground. The small ground units have been instrumental in calling in the precise air strikes [especially when Army Special Forces were augmented with Air Force combat controllers]. This emerging mission goes beyond the joint definition of CAS.
General Chuck Horner, the joint air commander during Desert Storm, likened it to giving infantrymen a "2000 pound hand grenade" (i.e., a 2000 pound JDAM guided bomb) from a long-range bomber loitering overhead.
Deconfliction is now a major function of several interoperating systems, including the Advanced Field Artillery Tactical Data System for the Army and Marines, the AN/SYQ-27 Naval Fire Control System for naval guns and gunnery, and the Air Force Theater Battle Management Core System.
- Richardson, Doug (February 1, 2003), "Summoning the Fire", Armada International
- Evans, Nigel F. (May 23, 2008), The computer age, British Artillery Technical Fire Control
- Joint Fire Support, 13 November 2006, Joint Publication 3-09
- Joint Tactics, Techniques, and Procedures for Close Air Support (CAS), 2 September 2005, Joint Publication 3-09.3
- Joint Tactics, Techniques, and Procedures for Laser Designation Operations, 28 May 1999, Joint Publication 3-09.1
- Rosenau, William (2000), Special Operations Forces and Elusive Enemy Ground Targets: Lessons from Vietnam and the Persian Gulf War. U.S. Air Ground Operations Against the Ho Chi Minh Trail, 1966-1972, RAND Corporation. Retrieved on 2007-11-11
- Theisen, Eric E. (2003). Ground-Aided Precision Strike Heavy Bomber Activity in Operation Enduring Freedom. Air University Press.
- Erwin, Sandra I. (April 2002). Air Warfare Tactics Refined in Afghanistan: Planners, air crews fine-tuning targeting techniques and rules of engagement. Retrieved on 2007-11-11.