Document created: 17 June 04
Air University Review, January-February 1970
Lieutenant Colonel Ross E. Hamlin
In the early stages of air warfare, vintage 1914, an
enterprising aviator dropped hand grenades over the side of his flying machine;
another airman took along a rifle and shot at enemy troops on the ground. Since
that time, quantum steps have occurred in the development of bomb-navigation and
gun systems. One facet of the evolution of gun systems is of particular
interest—the side-firing mode. Yet this concept had lain dormant for a number
of years. During World War II flexible side-firing weapons were used almost
exclusively on bomber aircraft as a defensive system in the air-to-air role.
Occasionally, a low-flying bomber would strafe, using its flexible mounted side
guns or turrets. The emphasis for air-to-ground gunnery was placed on fixed
forward-firing systems in the wings or nose sections of fighters and light
attack bombers. With
the advent of jet bombers (e.g., B-47 and B-52), the side-firing system passed
out of existence. These high-speed bombers relied on a tail turret for defense
against enemy fighters. Thus, it appeared that the mounting of guns in the sides
of aircraft was doomed to antiquity.
was not to be, however, for nearly everyone who has served a tour in Vietnam,
and many who have not, has been awed by the tremendous firepower of the AC-47
gun-ships, or “Spookies” as they are often called. The enemy was also
impressed, for after a few nocturnal encounters with a “Spooky,” he named it
“Puff the Magic Dragon.” This name is derived from the long tongues of flame
stretching nearly to the ground: the muzzle blast and tracer action from the
three fixed side-firing 7.62-mm miniguns. They are of the Gatling variety
and together fire 18,000 rounds per minute.
“Spooky” was the first in a new family of Air Force aircraft, the
side-firing gunships. Now we also have the “Shadow” or AC-119 G and K models
and, in the vernacular of Ed Sullivan, “the really big” AC-130 or “Spectre.”
Some wag at the Pentagon took a picture of the new giant C-5 transport, faked in
48 Gatling guns along one side, and speculated that the enemy might well
dub it with the acronym BUF (big ugly friend).
should not scoff at this apparently outlandish concept, for strange things have
occurred in the development of gunships. Consideration was given to bringing
some of the C-97s and C-121s out of mothballs and using them as gunships. The
other end of the scale of aircraft was looked at, too, for some favorable tests
were run with the small O-2 equipped with a side-firing minigun. The present
force structure calls for, in addition to the AC-47, the AC-119G equipped with
four 7.62-mm miniguns, and we also have the jet-engine-augmented AC-119K with
its four miniguns plus two 20-mm M-61 Gatling guns. Of course, the AC-130 with
its eight side-firing guns—four 7.62-mm and four 20-mm Gatling guns—is truly
an impressive weapon system.
did this all come about? And why all the sudden interest in using old and slow
transports? First, we had not been in Vietnam very long before it became
apparent that we had a problem in trying to support the “strategic hamlet”
concept. We found that during the day the Viet Cong would seldom venture forth,
and if they did our fighter aircraft tore them up. So like any smart guerrillas,
they turned to night operations. This created a major problem since there were
many, many hamlets but not enough fighter aircraft to provide protection.
Besides, the jet jocks were having their problems finding the black pajama crowd
and then hanging around all night. At the risk of alienating many friends with
“the big wristwatch and—,” they just did not have the staying power.
Tooling over the rice paddies at 400-plus at night was not conducive to pinpoint
target acquisition. We needed something that could circle over a village or an
outpost while we picked out which rubber tree the bad guys were leaning against.
We needed an aircraft that could carry its own flares or spotlight, and we
needed room for some pretty exotic sensors which were vastly improved over the
20/20 (?) vision of the tired fighter pilot. So people around the Air Force
started looking for a solution.
who dug into the problem thoroughly was Captain (now Lieutenant Colonel) Ronald
W. Terry, who was assigned to the Flight Test Section of the Aeronautical
Systems Division of AFSC, at Wright-Patterson, AFB, Ohio. In the course of
analyzing the close air support problem, he reviewed an old study that addressed
lateral sighting techniques. This paper was based on some observations by an Air
Force officer in a remote jungle village in South America. He had watched
medical supplies and mail being lowered on a rope from an aircraft to the
ground. The aircraft was flying in a modified pylon turn so that the end of the
rope remained nearly stationary over a point on the ground. This technique was
the basis for follow-on studies that led to the development of the current
side-firing gun systems.
To carry on with the evolution of the gunship, let us look at some of the advantages of this “new” system. First, the pylon turn geometry of the side-firing delivery mode allows the guns to be aimed at a ground target for extended periods of time while the aircraft maintains a constant altitude and slant range. This permits almost continuous target surveillance and suppressive fire from all sides. Further, a high degree of accuracy from extended slant ranges is obtained while reducing the exposure of the aircraft to enemy small-arms and automatic-weapons fire. Furthermore, the aircrew has ample time to operate the sensors and remain target-oriented, while devoting maximum attention to the firing problem. A corollary advantage is that the high angle of bullet trajectory increases the accuracy and effectiveness of the gun system. Finally, targets can be acquired, identified, and fired upon without descending to a lower altitude or overflying the target. (See Figure 1.) These advantages are extremely attractive, particularly when air operations are conducted in an environment where hostile fire is limited to small arms and light automatic weapons.
The progress made in sensor technology has enhanced the capability of gunships to assist in conducting tactical air operations on a 24-hour basis, weather permitting. This has always been a goal to which we have aspired but one that has not been easily attainable. The ability to acquire, identify, and then destroy fleeting targets during darkness or periods of low visibility has eluded us in the past. Now, however, we appear to be solving this troublesome problem.
Figure 1. Angles of attack
gunship development has been aided materially in this area because of its unique
side-firing capability and its large load-carrying capacity. It can carry
a large internal load of ordnance, including parachute flares and other devices
for illumination of night targets. In addition, it can handle considerably more
sensors and operators than can be accommodated by fighter aircraft. Another
important asset of these converted transports is their ability to fly for
extended time periods over the target. For example, a current application of the
gunship concept includes airborne alert with the subsequent ability to proceed
to numerous targets, spending considerable time in each area. Mission durations
of five to eight hours are common for these flights. Operator/technicians aboard
can make in-flight repairs or adjustments, thus improving the overall weapons
acquisition and identification
the AC-47, the first in the series of combat gunships in Southeast Asia, the
principal method of detecting and acquiring a target was by use of the human
eyeball. Dense foliage and camouflage made target detection difficult in
the daytime, and daytime operations did give the enemy the advantage of easily
tracking and firing at the large, slow gunship. This he did with disconcerting
frequency and accuracy. To lessen vulnerability from ground fire, the modus
operandi was changed to night operations. This was a compatible change, for
the fighters, though capable of good daytime close air support, were
having problems at night. With the changeover the problem of target acquisition
arose, so the AC-47s carried parachute flares, to the crew in making positive
AC-130 was the next gunship developed, and it had numerous more sophisticated
improvements in target-acquisition capability. It relied on complex electronics
systems to do this job. In addition, it too carried flares plus a large
spotlight for battlefield illumination. These systems gave the aircraft a
self-contained night attack capability. The AC-119 series had variants of these
the target has been acquired and identified, the next step is to place the
aircraft in the proper position for firing. This is the genesis of the gun
geometry problem. The pilot must approach the target from the side, and the
distance for offset depends on the desired slant range. Slant range is the
product of two factors: absolute altitude (actual distance above the
ground) and lateral distance from the target. To maintain the advantage
of a his angle of attack in relation to the target, guns are depressed in
relation to the lateral axis of the aircraft. The depression angle required at a
given airspeed is a factor of altitude and turn radius. For example, with
a 15-degree gun declination and a 30-degree angle of bank, there is a 45-degree
angle of attack on the target. Whenever possible, the guns are depressed at an
angle that allows some degree of flight deviation without diminishing
Another aspect of the gun geometry problem is the effect of projectile motion. The usual ballistic factors associated with any airborne gun are considered, e.g., wind effect, gun angle, slant range, bullet drop, etc. The side-firing gun introduced another problem, since the bullet leaves the muzzle at a 90-degree angle from the path of the aircraft. This induces a condition known as velocity jump. When the projectile leaves the gun, it will have two components of velocity with respect to air mass. These components are the muzzle velocity along the gun line and the true airspeed. The angle in mils between the muzzle velocity line and the projectile total velocity is called velocity jump. (See Figure 2.)
Figure 2. Velocity jump
All these factors make for a sizable “Kentucky windage” problem. In the AC-47 the pilot has to solve these problems as well as position the aircraft properly in relation to the target. In the follow-on aircraft, the AC-130 and AC-119, the solution to the gun geometry problem is made much easier and more effective through the use of a fire-control system containing a computer that provides aiming and steering information to the pilot. The computer interprets the inputs from any one of the sensors to establish a line of sight to a designated point. The computer receives values of aerodynamic wind, true airspeed, and altitude; compares the line of sight with the corrected gun line; and provides position and altitude guidance information visually to the pilot through an instrument landing system (ILS) indicator and a gunsight. (See Figure 3.) Certainly this is a vast improvement over the earlier system, and current plans call for retrofitting the AC-47s with a modified fire-control system similar to this one
Figure 3. A computerized firecontrol system
for the AC-199 and AC-130 helps the
pilot solve the gun geometry problem. A similar system is planned for the AC-47 gunship.
considering these improvements, let us further compare gunships. The AC-47
carries three 7.62-mm miniguns, each of which can fire either 3000 or 6000
rounds per minute. The pilot has a gunsight by his left shoulder and a trigger
on the control column. Gunners are crew members on all gunship missions, and
they reload and clear jammed weapons; however, they cannot fire the guns.
AC-130 has much greater firepower. It carries four 20-mm M-61 Gatling
guns and four 7.62-mm miniguns. The 20-mm weapons are very effective against
trucks, small boats, and light structures.
AC-119G armament consists of four 7.62 miniguns, and its sister ship the AC-119K
carries, in addition, two of the 20-mm Gatling guns. The “K” model differs
from the “G” in the addition of two J-85 jet pods, which give it
approximately 25 percent greater load-carrying capacity and a significant
increase in single-engine performance. Aircrews operating at night off small
airfields and in narrow mountain valleys greatly appreciate this factor.
Examination of gunships to this point has concentrated on their evolution and how they work. Let us look now at how they are employed, what specific missions they perform. The versatility of the side-firing gunship has made it possible to adapt the system to a variety of missions, including dose air sup-port, interdiction, aerial blockade, and base defense. A close look at some gunship missions will highlight the special flexibility of this new “machine.”
Close air support. An essential requirement of close air support is that it be readily available and effective when and where needed. It must be responsive to ground needs, easily obtainable, reliable, and suitably armed; above all, it must be able to strike targets in close proximity to friendly ground units during any condition of ground maneuver and fire. Presently no single Army or Air Force system is capable of doing these things economically during darkness and adverse weather. Yet the gunship in the close air support role has achieved a reputation for its responsiveness, fire support, battlefield illumination and surveillance, convoy escort, airmobile operations, and search and rescue operations.
things, is the capability to react quickly to requests for fire support to meet
unexpected contingencies in ground operations. For aircraft on strip alert,
responsiveness is a factor of basing distance, cruise speed, command and control
procedures, and the time to acquire and strike the target. The gunship cannot
compete with other systems in response time, unless it is on airborne alert over
or near the maneuvering forces. Yet from this posture, it can proceed to the
area of engagement in a matter of minutes and deliver automatic-weapons fire on
a target in minimum time.
should be airborne over the forward edge of the battle area (FEBA) or over
maneuvering forces when it is believed that contact with the enemy is probable.
With its large payload and fuel capacity, the gunship can remain in the battle
area for extended periods. In addition to being available for automatic-weapons
fire, the constant presence of a fire support aircraft with appropriate sensors
provides strong suppressive and deterrent effects on the enemy and puts him at a
distinct disadvantage in initiating offensive actions.
reduce delays inherent in command and control procedures, the gunship on
airborne alert will have prior clearances from the Tactical Air Control System (TACS)
to respond to any request from the maneuver force commander or the fire support
director. If necessary, a forward air controller (FAC) will be aboard the
gunship, or a crew member of the gunship will be qualified as a FAC. Common
communications equipment, maps, and procedures will ensure effective
coordination between the maneuvering unit and the gunship. As they are only a
short time on station, gunship crew members must be familiar with the situation
on the ground and the locations of friendly and enemy forces. Constant
monitoring of ground radio frequencies will keep them up to date with the
ongoing actions, even in a rapidly changing combat situation, thereby
providing immediate response to the ground commander.
mix of 7.62-mm and 20-mm high-explosive (HE) automatic weapons and the system
accuracy make its fire support very effective against enemy personnel and
many other targets normally encountered along the FEBA or in close proximity to
friendly forces in combat. When necessary, flash fires (direct fire on
friendly troops when covered by bunkers) can be used. This technique is
effective when defending fortifications against over-running troops in the open.
Against enemy troops in foxholes, trenches, or under light cover, the gunship’s
high angle of bullet trajectory, plus the high rate of cannon and machine-gun
fire, enhances its effectiveness in delivering enfilading automatic-weapons
fire. The AC-130, for example, can fire one or any combination of its eight
guns. When all eight are placed on rapid fire, the effect is devastating.
In its battlefield surveillance and illumination role, the
gunship with its sensors can detect targets in the battle area which cannot
otherwise be observed in real time from the ground or air, particularly at
night. The gunship can respond to ground requests to investigate suspected
areas and suspicious activity. In this way the ground commander can be informed
via secure communications of enemy activity in the area.
conjunction with battlefield surveillance, the gunship can provide the ground
commander with on-call battlefield illumination by flare or spotlight. Enemy
troops can be pinned down, and hard point targets can be detected and
illuminated for fighter attack. (See Figure 4.) Thus, a gunship’s usefulness in
close air support can extend beyond the time its ammunition is expended. Instead
of returning to base immediately, it can continue to search for targets and
illuminate and mark them for fighter strikes until it is relieved by another
Convoy escort is
the protection of ground forces that are in movement. The aircraft must maneuver
ahead and to the flanks of the column, search for and neutralize threatening
targets, and warn the convoy of impending danger. While escorting, the gunship
circles over and ahead of the convoy, scanning the area along the route with its
sensors. It can observe suspicious conditions and road blocks and detect
ambushes, particularly at night. The gunship has an advantage over light
aircraft for convoy escort because it is able to scan a larger area with greater
thoroughness and bring automatic-weapons fire on enemy threats to the convoy.
The gunship can assist fighters and armed helicopters in providing
security to forces engaged in airmobile operations, especially in jungle
or sparsely populated terrain. The gunship plays a role in each phase of
air-mobile operations: the preassault, assault, and withdrawal phases.
the preassault phase, after the primary and alternate landing zones (LZ)
have been selected, a large aircraft capable of carrying the required number of
real-time readout sensors can survey the surrounding area for signs of enemy
activity and pinpoint the locations of enemy units. With long-range sensors,
this can be done at higher altitudes and over larger areas; such intelligence is
invaluable to the airmobile commander. Just prior to the assault, and as part
of the LZ preparation, definitive airborne sensors should be employed to
determine if enemy troops are waiting in ambush or are in the vicinity.
the assault phase, a gunship can cover the helicopter landings and
disembarkment of troops. Using its communications and ability to survey and fire
from an orbit high above the operations, a gunship could possibly serve as an
airborne command post, radio relay unit, and forward air controller. It can also
maintain security for helicopter resupply and medical evacuation for the forces
on the ground and protect base camps at night.
support during the withdrawal phase is similar to that during preassault
and assault phases and depends upon the circumstances under which the withdrawal
The gunship offers unique capabilities for supporting search and
rescue operations. With its numerous sensors, it can aid in locating downed
airmen, especially at night. It can provide illumination, should it be desired
for a night extraction, and it can also provide suppressive fire to allow a
helicopter or other rescue forces a chance to effect the rescue. As in airmobile
operations, the gunship can perform a multitude of roles. Probably its
most singular advantage is its ability to operate effectively under poor weather
conditions and darkness.
and armed reconnaissance.
low-threat environments, the gunship operates alone at night. It can fly
relatively long distances to an area and still have sufficient endurance to
search along the line of communication (LOC) for trucks, POL dumps, supply
areas, truck parks, and vehicle repair shops.
higher-threat areas, an optimum concept for night interdiction is to have
several gunships search for targets in conjunction with fighter aircraft. Either
the fighter can be directed on a target, or it can provide flak suppression for
the gunship. This joint effort is very effective for attacking enemy LOC’s.
allied to the interdiction mission is the concept of aerial blockade where the
object is to reduce enemy infiltration and resupply by inflicting casualties
and destroying supplies and transport. The political developments in Southeast
Asia have brought about increased emphasis on the use of the aerial blockade.
The Free World forces in South Vietnam are now faced with trying to choke off
the enemy flow of men and materiel from several politically protected
sanctuaries. The provisions of any truce arrangement could be enforced by an
effective aerial blockade.
Figure 4. A spotlight recce/strike
gunships offer excellent capabilities for this mission with their sensors,
firepower, and extended flight duration. They can team up with other methods of
surveillance to apply continuous coverage of points of entry along enemy
borders. If border violations arise that require immediate use of firepower,
gunships can provide instant and accurate response.
base defense, other than normal security measures against saboteurs, entails
protecting the base from ground attack and mortar, rocket, and artillery fire.
Although the type of defense used depends upon the demographic environment of
the base, the mission can be considered as preventing or stopping attacks.
of attacks is the most desirable course if it can be accomplished without undue
consumption of resources. The use of ground forces for the sole purpose of
preventing mortar or rocket attack is wasteful and not too reliable. Airborne
visual surveillance in conjunction with ground patrols is slightly more
effective. Airborne sensor surveillance, along with the other efforts, is still
many instances the gunship sensors can detect enemy positions at night while
they are being prepared or emplaced. In the event an enemy attack is already in
progress, the gunship can again be employed to good advantage.
a mortar or rocket position quickly is imperative to minimize damage to
base facilities, personnel, and parked aircraft. The ability to do this is a
function of target acquisition, time to engage, and effectiveness of suppressive
fires. The gunship, on airborne alert over the base, offers a good solution.
With its sensors, long loiter time, and excellent firepower, both in terms of
accuracy and volume, it provides effective and rapid response. This kind of
reaction degrades mortar/ rocket crew performances and serves as an excellent
deterrent for subsequent attacks.
detection and tracking will continue to be a major problem in the interdiction
mission, particularly under the weather, terrain, and foliage conditions
commonly found in Southeast Asia.
advances in sensor technology have been made since the gunship prototype was
first introduced in SEA. System effectiveness can be improved by utilization of
sensors that can operate during inclement weather and by the use of improved
weaponry (i.e., improved ammunition and larger-caliber guns with an improved
fire-control system). Flexible turrets for sensors and weapons are also a
possibility. Who knows—perhaps we saved some of the ball turrets from
the B-17s and B-24s of World War II!
improved weaponry and new sensors will make the gunship less vulnerable in that
more lucrative targets can be destroyed from greater standoff ranges and during
inclement weather. At the same time, new and refined employment tactics will
evolve that will confirm the role of the gunship along with that of the tactical
fighter. Because of their different characteristics and
capabilities, the gunship and tactical fighter complement each other. Gunships
are primarily for night operations, tactical fighters for day operations.
Working together, gunships can operate in more hostile areas with fighter
protection or increase fighter effectiveness at night by being the eyes, ears,
and pointer for fighter operations.
by placing gunships in strategic areas, we will have the capacity to provide a
rapid response to developing crises. The gunship’s long-distance ferry range
reduces its dependence on base and overflight rights for deployment to distant
places in the world. Once there, it can operate on austere civilian fields if
necessary. Its automatic-weapons fire presents a considerable military
capability without being provocative.
Hq United States Air Force
Lieutenant Colonel Ross E. Hamlin (M.P.A., George Washington University) is assigned to the Office of the Special Assistant for Counterinsurgency and Special Activities, Joint Staff, JCS. After flying training, 1944, he flew B-24s and B-29s until 1946. Subsequent assignments include B-26 pilot, Korea; K-97 pilot, Strategic Air Command, 1956-59; Assistant Air Attaché, Taiwan, 1959-62; Faculty Member, Air Command and Staff College, 1963-67; Commander, AC-130 unit, Southeast Asia; and Air Staff Officer, Special Operations Plans and Policy Branch, Directorate of Plans, Hq USAF. Colonel Hamlin has been selected for promotion.
The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.
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