The art of air-to-ground attack was born in the smoke and flames over World War I battlefields, when low-flying fighter pilots used machine guns to strafe enemy troops in the trenches. The troops, of course, fired back at the fighters. At about the same time, airmen began to perform rudimentary, level bombing from two-seater aircraft. The pilot guided the biplane over a target, and the observer, leaning out of his cockpit, hand-dropped small bombs on troop formations, road intersections, buildings, bridges, and other "strategic" targets. By the end of the war, military airmen had developed simple bomb racks for larger bombs, which were fastened under the wings or fuselage of a plane.
Level bombing was not very accurate at the time, mainly because there were no reliable ranging systems. After the war, the US Navy developed dive-bombing, which was more accurate, and the modern form of warfare, now called "tactical surface attack," began. The pilot could aim a bomb at a target, release it, and pull out of his dive at reasonable risk (for a fighter pilot), in hopes of being above the lethal envelope of small-arms fire, but he had to maintain a steady course as he flew along his delivery path toward the release point over the target. This requirement made a diving plane vulnerable to antiaircraft fire, which rose much higher than small-arms fire.
The aircraft's vulnerability was lessened somewhat by its rapidly changing altitude. This complicated the defender's firing task, because each antiaircraft round was preset to detonate at a specific altitude. A round might be well aimed, passing near the aircraft, but if it exploded at an altitude that was significantly different from that of the diving plane, it was ineffective.
The Proximity Fuze
Eventually, military technicians invented proximity fuzing for antiaircraft rounds. Proximity fuzes could sense the nearness of a targeted aircraft and detonate the warhead, no matter what its preset detonation altitude. The tactical pilot's risk increased considerably. Further, the development and refinement of radar during and after World War II meant that the enemy could know attackers were coming. Advance warning mitigated a key attack advantage: the element of surprise.
Next, fire-control radar was integrated to provide exact target altitude and bearing information to antiaircraft batteries, making their fire more deadly.
The risk to aircraft rose exponentially with the development of surface-to-air missiles (SAMs) and their extensive employment by North Vietnamese forces during the Vietnam War. With direction from a combination of on-board and site-located radar, the missiles could accurately track US fighters. The best way to defeat the SAMs, US pilots found, was to outmaneuver them and dive for the earth. This put the Americans within reach of potentially devastating small-arms fire. As a result, US pilots faced a deadly threat both high and low. They could fly low only in daylight because of the danger of flying into terrain that was not visible at night.
Fortunately, the US developed equipment that returned some of the advantage to the pilot. Soon perfected were new inertial navigation systems that could accurately keep track of a fighter's position, even in constant high-G maneuvering. Onboard air data computers, which gathered sensor information on air temperature and density, were added. A central computer could use inertial navigation system information, combined with altitude, wind direction and speed, and data from ground-mapping radar, to tell a pilot his exact position and the position of the target. The central computer, manipulated by the pilot, could direct armament systems to employ weapons.
Today, cockpit video displays, navigation radios, sensors, onboard computers, ground-mapping radar, forward-looking infrared systems, inertial navigation sets, integrated tactical electronic countermeasures devices, and programmable armament control sets are standard equipment aboard modern surface attack aircraft such as USAF's F-15E. These enable the fighter pilot to strike a target with precision. In many cases, they can employ certain types of ordnance without having to fly over a heavily defended target.
Using the two-pod AN/AAQ-13/14 Low-Altitude Navigation and Targeting Infrared for Night (LANTIRN) system, a two-man F-15E crew can take off from a blacked-out airfield and fly a moonless night attack mission only 100 feet above rough terrain, traveling at airspeeds greater than 500 knots. The infrared picture, which the pilot sees through the head-up display (HUD) in his windscreen, "reads" heat emissions to show him the terrain ahead, which shows up almost as bright as in daylight.
The terrain-following equipment enables the pilot to stay below enemy radar acquisition horizons. Once in the attack area, the aircrew can "see" the target, using ground-mapping radar or infrared return data displayed on one or more of their cockpit multifunction displays (MFDs), and attack it before the defenders know they are threatened.
Even as the pilot flies his high-performance aircraft, the fighter crew must manage all the modern avionics and electronic systems at its command, interpret information provided by the sensors, make attack decisions, and, finally, operate all the systems necessary to carry out the mission.
Today almost all ordnance deliveries are made using the "magic" of the systems in the aircraft. Pilots train to use it every day. Nevertheless, because battle damage or other factors may cause the systems to fail, the pilot must practice delivering bombs the old-fashioned way, in the manual mode. The job remains the same: Put ordnance on the target, regardless of what the defenders throw at the attacking fighter.
The "Pucker Factor"
This job-attacking a ground target from a fighter-might seem simple. After all, a streamlined projectile dropped from an aircraft will follow a predictable trajectory to the target. All the pilot has to do is put the aircraft's release position exactly where it should be to make sure the trajectory's starting point is correct. Getting to that point, however, is not a simple task, even if the pilot doesn't have to contend with the "pucker factor"--stress--induced by flak, enemy interceptors, and SAMs.
To determine the release point for its bombs, the aircrew starts with the target's altitude. Crew members know they must release at a high enough altitude above the target for the bombs to arm. If the bombs are not armed, they will not detonate. One often-used arming setting is six seconds. The pilot also knows that he must release at an altitude high enough to permit him to pull out of the dive and still be above the fragmentation envelope of the bombs.
From precomputed tables, the pilot can determine, for example, that the fragments from a detonated Mk 82 500-pound bomb with an M904 fuze will radiate in all directions at 1,30 feet per second in the first second after impact. By nine seconds after impact, slowing down be- cause of friction with the air, the fragments will have traveled 2,520 feet vertically. The pilot will be pulling out of his dive during this time. He knows he must "bottom out" at least 2,520 feet above the target altitude. Actually, when he includes a safety factor of twenty-five percent, the altitude is 3,150 feet above tart altitude.
Another table tells him that, if he bombs with a forty-five-degree dive angle, and if he applies 4.5 positive Gs to the aircraft within two seconds after release, he will need about 2,000 feet to pull out of the dive. Thus he knows he must release the bombs and start his pullout at just over 5,000 feet above target (3,150 feet plus 2,000 feet). The bomb trajectory differs according to airspeed, so the pilot always strives to release at the same speed in manual bombing--around 450 knots. In this way, he can develop a "grooved" delivery, much the same way that a golfer develops a grooved swing. (With automatic systems operating, the pilot can vary his delivery parameters considerably and still bomb accurately. This, of course, is highly desirable, in that defenders in a hot war cannot divine a predictable pattern that an attacking aircraft will follow.)
To reach the exact delivery point for accurate bombing, the pilot probably finds he must start his roll-in from a point 10,000 or 11,000 feet above the target. This gives him time and airspace to bring the nose of the aircraft down and around to the proper aiming and delivery position.
Shorts and Longs
It is critical that the pilot hold the aircraft in the exact computed dive angle and exact computed airspeed until he releases his bombs. When he holds his aiming "pipper" on the target and he is traveling too fast or diving too steeply, his bombs will be long or will hit-past the target. If he is too slow or too shallow, his bombs will fall short. For example, a dive angle that is five degrees shallow (forty degrees) will cause the first bomb to hit about 130 feet short. If the pilot is twenty knots slow, the first bomb will hit sixty feet short. If he is exerting unwanted G-forces on the aircraft (perhaps starting the pullout too soon), the bomb impact point is affected. Exerting only one-fourth of a G at the release point can cause the first bomb to be almost forty feet short of the target. Pilots try to compensate for deviations in release conditions by moving their aiming point.
Often complicating the situation are crosswinds, headwinds, and tailwinds. At altitudes above 3,000 feet, winds of forty knots or more are common. The aircraft, like a canoe caught in the current while being paddled across a swiftly flowing river, is significantly affected by the air mass through which it is diving. A forty-knot wind from the left, for example, will displace an aircraft's diving flight path toward the right. The winds have negligible effect on the bombs as they fall through the air mass. But the bombs will tend to follow the sideways flight path of the aircraft at the release point, so the pilot has to aim to the side of the target to compensate.
Doing this accurately is not easy, especially in light of the fact that winds rarely come in directly on the nose or tail, or from ninety degrees to the centerline. They usually are quartering winds, and it is difficult to apply a correcting rule accurately. Because of these complications, before the advent of modem computerized bombing systems like those in the F-15E, many pilots used an aiming system they jokingly called the TLAR System. TLAR meant "That Looks About Right. In the past, complicating factors notwithstanding, dive-bombing qualification required an average "miss" of less than 140 feet from the pylon in the middle of the bombing circle. Most pilots had average accuracies of fifty feet or less, and many regularly scored bull's-eyes.
During the Vietnam War, accuracy diminished somewhat because the defenses often dictated release altitudes well above those used on the practice range. Foul weather over the targets often forced unusual release altitudes or attack patterns. Pilots were able to compensate for these by releasing multiple bombs, some of which would fall short or long, with others in the string hitting the targe
In South Vietnam, Cambodia, or Laos, many of the targets that were attacked were "targets of opportunity" located by a Forward Air Controller (FAC). The FAC would estimate target altitude by looking at his map. Over the radio, he would obtain estimated pressure altitude and winds from the command center. He would pass this information, with target coordinates and map location, to an incoming attack flight. While the FAC was marking the target with a smoke rocket, the flight members would prepare for the attack. Often, if there was fuel and time, the flight leader would drop one bomb, observe its impact point in relation to his aiming point, and then advise the rest of the flight on sight settings and offset aiming points.
In the late 1960s, modem computers, avionics, and attack systems began to appear in US fighters in southeast Asia. The venerable Republic F-105 Thunderchief, workhorse of the war over the North, was equipped with the Thunderstick modification, which gave it a computerized toss-bombing system. The McDonnell Douglas F-4E, with an internal gun and a computerized bombing system, was introduced and provided a significant increase in attack capability.
In late 1972, the LTV A-7D, which represented a quantum leap in the sophistication of ground-attack fighter aircraft, was introduced in the Vietnam War. The A- 70 featured an extremely accurate inertial navigation system, a HUD, and a weapons employment system unparalleled at the time.
In the A-7, computerized systems automatically compensated for the effect of winds and other atmospheric conditions and easily accommodated varying roll in direction and altitudes, release altitudes, and airspeeds. It featured a terrain-avoidance system and a reliable radar all-weather bombing system. Equipped with the first truly accurate toss-bombing capability, the A-7D was the forerunner of to day's F-16 and F-15E. The A-7D and the F-4 are still flying.
How the F-15E Does It
Today, because of the greatly increased capability of on-board navigation and ordnance employment systems, an F-15E attack fighter aircrew spends more time than ever in flight planning. In flight, the pilot and his weapon systems officer are busy managing the systems.
Assume the target is a vital, heavily defended railyard, 200 miles inside mountainous enemy territory. The takeoff time is three a.m., and there is no moon. No landmarks will be visible, and all towns and cities will be blacked out because it is war- Although several varieties of precision- guided munitions might be suitable, including some that are powered, assume that the best ordnance available for this mission is the M117 750-pound "iron" bomb. The F-15E can carry at least twelve of them while still carrying a full complement of AIM-120A Advanced Medium-Range Air-to-Air missiles (AMRAAMs) for its own defense.
To fully exploit all the capabilities of the aircraft, every aspect of the low-level flight must be planned in advance, especially the location of navigation reference points along the route and the initial point for the start of the bombing run. The system enable the pilot to fly at low levels, over mountains and through valleys, all the way to the target at night. Staying beneath enemy radar, he uses ground clutter to fool any searching aircraft that might be equipped with look-down, shoot- down radar systems.
The aircrew can briefly pop up to an altitude from which the plane's on-board radar can take and "freeze" a picture of the target that is as crisp as a photograph. Then they quickly drop down into ground clutter again. The central aircraft computer, gathering input from on- board sensors, continuously gives their position in relation to the target and to the initial point for the attack.
Next the pilot must exactly locate the bombing pop-up point, from which he can start the ordnance- delivery phase of the mission. There he initiates a precise, forty-five-degree climb for a specified number of seconds to the pull-down point, where he then must roll the aircraft inverted and pull the nose down and around toward the target. From pre-flight planning, he knows the direction and distance to the target. From observation of the target, if it is visible, and from his HUD symbology and other information (presented on the aircraft's MFDs to the pilot and his backseater), he must determine whether the aircraft systems are, indeed, directing him precisely to the target or if they may be slightly off. If they are off, he must use some of the buttons and switches on his throttles and stick to align the aiming and release systems correctly.
He then smoothly rolls the aircraft upright, with the nose pointed down at the preplanned dive angle (or close to it), making sure the aiming symbol in the HUD is on the target.
The systems will use data from the aircraft's sensors to compensate continuously for climb and/or dive angle, airspeed variations, distance from the target, and wind effect. The pilot's job is to be sure the aiming symbol stays on the target and then smoothly to follow directions from his HUD symbology that tell him whether to fly left or right. When he depresses and holds the "pickle button," the system will release the bombs at the proper point to enable them to "fly" to the target. This job is much harder than it sounds, and doing it right requires a delicate touch on the controls and nerves of steel.
When the pilot gets an in-range indication in the HUD, and the release cues are flashing, he depresses the bomb-release button on the stick grip and starts the pullout. When the fighter reaches the precise point that will enable the twelve bombs to "fly" to the target, the armament system ejects them. Aircraft inertia tosses them toward the target, still a mile or more away; The time on the stabilized release heading is less than five seconds. Then the pilot aggressively rolls the aircraft to start his turn away from the target and enters the egress route.
Back at the target, the bombs erupt in a destructive pattern that blows up rolling stock and puts huge craters among the twisted and shattered railroad tracks. The rail yard is disabled. Antiaircraft guns are firing blindly. They don't have a target, because the attacking aircraft did not fly over their lethal horizon for more than a few seconds. The F-15E and its aircrew escape to fight again.
For the task of surface attack, the US is developing new aircraft such as the A-12 Advanced Tactical Aircraft. These planes will have even better capabilities, and they will be flown by a modem breed of tactical fighter pilots. Their mission will remain the same: Destroy the target.
Daily Report: Read the day's top news on the US Air Force, airpower, and national security issues.
Tweets by @AirForceMag