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Altitude, altitude..." Every pilot of a modern fighter aircraft has heard the soft female voice of the cockpit warning system indicating that the aircraft is too near the ground. For commanders, altitude is a tactical commodity, traded for time, accuracy, and survivability. The goal is to pick the operating altitude that gets the mission done while giving the aircrew as much control as possible over the risks and benefits of the battlespace.

The United States fought low-casualty air wars over Iraq in 1991, Bosnia in 1995, and Yugoslavia in 1999. Operations Desert Storm, Deliberate Force, and Allied Force, respectively, put a new twist into the question of altitude. Critics of Allied Force claimed airmen compromised accuracy-and integrity-by flying at 15,000 feet to avoid air defense threats.

"I was very frustrated with [the] preoccupation with altitude as if that were a measure of commitment," remarked Maj. Gen. (sel.) Daniel P. Leaf, commander of the USAF wing at Aviano AB, Italy, during Allied Force.

A year later, during the 2000 Presidential campaign, Sen. John McCain (R-Ariz.) said this: "The most obscene chapter in recent American history [was] the conduct of the Kosovo conflict, when the President of the United States ... had them flying at 15,000 feet, where they killed innocent civilians because they were dropping bombs from such high altitude."

In fact, altitude is not a linear guide to justice in war. Risk is present at all altitudes and the choice of altitude for a mission is a complex tactical calculation constantly reviewed by pilots and commanders as they seek the best way to get the job done.

No Man's Land

During the Cold War, pilots trained extensively to fly at low altitude. Systems as diverse as the F-111 fighter-bomber and the B-52 heavy bomber practiced with terrain following systems to improve their proficiency in flying low and fast. Pilots knew that the airspace from 500 feet to 5,000 feet was No Man's Land: It was constantly endangered by small-arms fire, anti-aircraft artillery, and handheld surface-to-air missiles like the SA-7 and SA-14.

At that time, the idea was that, at least for the first few nights of the war, aircraft would fly low and fast. Then, attacks on the enemy's integrated air defense system were supposed to reduce the threat at medium altitude. Meanwhile, technological breakthroughs in electronic countermeasures, anti-radiation missiles, and later, stealth sought to reclaim the optimal airspace at medium altitude.

On the eve of Desert Storm, USAF was still training to go low and fast. An F-111F pilot commented that, while he and other pilots trained for both medium and low altitude, "80 percent of our training was for the low-level altitude environment."

Air Force Lt. Gen. Charles A. Horner (now retired general), the Joint Forces Air Component Commander in the Gulf War, actually raised the training altitude restriction from 500 to 1,000 feet in October 1990. He did so after the US experienced a pair of training accidents. However, he allowed the B-52s to continue training at 500 feet.

Whether to fly low depended on the aircraft, the weapons, and the attack profile. Early in the war, an RAF Tornado pilot described attacking an airfield at "520 knots and 180 feet radar altitude, through what seemed to be a solid red and white wall of tracer."

The RAF pilot had to fly low because the attack employed JP233 mines optimized for delivery at about 200 feet. Although this RAF crew survived the fireworks display, three Tornados were lost in low-level attacks. On the war's second night, a B-52 at low altitude had to turn back from its target in the face of heavy gunfire.

Gulf War planners concluded that risk and mission accomplishment factors did not favor low-altitude attacks because there were other ways to do the job. Units shifted to medium-altitude tactics. While Horner did not order the change, he gave it his approval and told the RAF specifically after the first few days that their low-altitude losses were unnecessary. As it turned out, the Desert Storm air campaign planners "would largely abandon low altitude in favor of altitudes above 10,000 feet," said the Gulf War Air Power Survey.

More to the point, the premier fighter-bombers of 1991 worked best at medium altitudes. The stealthy F-117 specifically was designed to fly above small-arms fire and to survive the SAM threat at medium altitudes. Precise delivery of its laser-guided bombs required room to work. From an altitude of 15,000 or 20,000 feet, the pilot had time to identify the target and guide in the weapon. The laser-guided bombs needed time to leave the aircraft, acquire the laser-spot, and fly in to the target, within launch parameters that required steady flight. Dropping a laser-guided bomb outside the launch window would result in a miss.

Time to Target

The point is that an F-117 streaking over a target at an altitude of 1,000 feet would rob the pilot and weapon of the time needed to acquire the target. Stealth helped reclaim the preferred airspace from 15,000 to 25,000 feet, and for precision attack, medium altitude worked best.

For F-111Fs with the Pave Tack pods, the case was much the same. Whether attacking fixed targets or "plinking" Iraqi tanks, medium altitude--neither too low nor too high--was essential for accuracy. Moreover, early attacks on Iraq's integrated air defense system reduced the impact of its surface-to-air missiles, the deadliest weapons for medium- and high-altitude aircraft.

In contrast with F-117 and F-111F, F-16 and F/A-18 fighters had no precision targeting pods at the time of the Gulf War. When they attempted higher altitude deliveries, their accuracy suffered.

In the Kuwait Theater of Operations, where the bulk of the sorties were flown, aircraft at first generally flew above 15,000 feet. A need for greater accuracy pushed them lower. On Jan. 31, 1991, A-10s were ordered to drop down to between 4,000 and 7,000 feet for weapons delivery. F-16s were told to release bombs below 8,000 feet.

Going Low

What caused the change in tactics was the need to pick out targets by eyesight in the Kuwait kill boxes. "The lower altitude allowed the A-10 pilots to find their targets more easily than before, and the tank kills rose," Horner later wrote. After the change, the attrition of Iraqi military equipment picked up pace, and so did battle damage to the A-10s.

During the ground war of Feb. 24-28, 1991, aircrews once again went very low. Horner told the aircrews to fly as low as needed, saying, "You have a sacred duty to help the men on the ground. ... Now is the time for you to risk your jet, to risk your life, because they are down there engaged in combat and are for sure risking their lives."

Desert Storm demonstrated that altitude would now be considered a controllable variable in mission effectiveness. With precision weapons, medium altitude was the most effective place to operate. There were, to be sure, some drawbacks. Overcast weather hampered precision bombing when cloud layers disrupted infrared targeting. Still, the trend was clear. The best periods of sustained attrition bombing of Iraqi tanks came from the F-111Fs and F-15Es with laser-guided bombs working at medium altitude.

Four years later, the prosecution of Operation Deliberate Force in Bosnia saw a jump in the percentage of precision weapons employed. By then, most Air Force and many naval aircraft had precision targeting pods. The attacks on fixed targets in the air campaign ending in September 1995 were conducted almost entirely from medium altitude.

The air campaign known as Operation Allied Force began in March 1999 with a directive ordering pilots not to fly below the established "floor" of 15,000 feet altitude. USAF Lt. Gen. Michael C. Short, the JFACC, noted that the NATO allies agreed that it would be a precision campaign insofar as possible. With laser- and GPS-guided bombs, Short said, "we would ... be as precise and as accurate as we could." The idea was to accept legitimate risk but avoid the squandering of aircraft and pilots by exposing them to small-arms fire, anti-aircraft fire, and man-portable SAMs.

"The first measure of merit is not to lose aircraft," directed Gen. Wesley K. Clark, US Army, Supreme Allied Commander of NATO forces. Clark's directive drove decisions on tactics for the air war. "We had all agreed that 15,000 feet was going to be the floor," Short said.

"We started with 15,000 feet and it worked OK," Leaf recalled. Attacks on fixed targets were no problem unless cloud layers slipped between the strike aircraft and the target. Bad weather early in the campaign forced a number of canceled missions. Except for the GPS-guided Joint Direct Attack Munition on the B-2, all the precision munitions employed by the Air Force were line-of-sight, meaning, as Leaf said, "you had to see the target to guide it."

More challenges came when NATO airmen initiated serious attacks on the Yugoslav 3rd Army. In the Kosovo Engagement Zone "we had to find and identify and strike targets," said Leaf. The 15,000-foot restriction "became more difficult" in the dynamic attack environment.

"I don't mean that we had to get down to 500 feet AGL [Above Ground Level] or 5,000 feet AGL," Leaf explained, "but that [staying about 15,000 feet] was a pretty challenging rule to live by in the KEZ, where you were finding and locating targets."

One F-16 pilot told reporters that seeking targets was like bungee jumping from the top of a building and trying to pick out details on the way down.

Then came the April 14 incident at Djakovica. At midday, forward air controllers spotted a large convoy of vehicles moving along a road. Airborne controllers in an EC-130 verified that the convoy was "VJ"--meaning Yugoslav Army--and cleared several fighters to attack the vehicles. The fighters employed laser-guided bombs from 15,000-foot altitude. The pilots were emphatic that, from the attack altitude, to the naked eye, they appeared to be military vehicles. At least one F-16 reported taking fire from anti-aircraft artillery near the convoy.

However, controllers called off the engagement when intelligence specialists at the Combined Air Operations Center said that VJ forces did not normally travel in such large convoys. An OA-10 was sent in to check the column and reported military and possibly civilian vehicles. The attack was terminated. The Serbs immediately reported civilian casualties from the air attacks. Subsequent investigation showed that at least one vehicle had been misidentified. There had been two convoys in the area, with a mix of military and civilian vehicles. Clark later wrote that the truth about the number of civilians in the columns might never be known.

International criticism instantly focused on the fact that the airmen operated under an altitude restriction.

Short felt responsible. He later said, "Under the limitations I had placed on the crew to stay above 15,000 feet and to let the forward air controllers go down to 10,000 feet for excursions, it was inevitable that we were going to drop a bad bomb." Short called Leaf at Aviano within hours of the incident and said, "I've been too restrictive. ... How do I need to change the rules?"

Relaxing the Rule

According to Short, Leaf advised him, "We needed to let the forward air controllers go down to 5,000 feet and to let the strikers go down as low as 8,000 feet in a diving delivery to ensure that they verify their target."

The new rules were implemented immediately via special instructions to the NATO airmen. When the change came, Operation Allied Force was just in its fourth week of operations. More than 85 percent of the sorties in the Kosovo Engagement Zone were flown under the new, broader guidance that gave aircrews expanded flexibility.

Those who flew on the forward air controller missions, as Leaf did, were pleased with the change. "It was good to have that flexibility," he said. "You went down to that altitude when you needed to be there, and you spent as little time as possible down there."

Even with the new guidance, however, medium altitude often was the right place to be. "You still tried to keep a nominal operating altitude above 15,000 feet," said Leaf. "We didn't want people just cruising around at 5,000 feet AGL, the heart of the man-portable infrared missile regime. But if you had to get the mission done, you had to get the mission done."

The Djakovica incident sparked an ugly and ongoing debate on operating altitude. It became a flashpoint for highly publicized charges that, by restricting their altitude, NATO airmen were in some way shirking their responsibilities.

NATO immediately apologized for the incident and released extensive details on the confusing engagement. Still, accusations about the moral implications (such as McCain's) continued. Commentators failed to pick up on the change in altitude rules or the fact that airmen often found themselves in danger even at higher altitudes. Retired Marine Corps Lt. Gen. Bernard E. Trainor wrote of being discomfited by events, saying, "High-tech weaponry permitted pilots to fly high out of harm's way while visiting destruction below." To Trainor, this development had "troubling moral and political implications" because the air campaign could "drive an enemy to his knees without shedding a drop of the bomber's blood."

700 SAM Shots

Trainor's sensitivities notwithstanding, the fact is that Allied Force strike missions were risky and pilots were not "out of harm's way" by any means. President Clinton said, "I was surprised that we'd lost only two planes and no pilots." Serbian gunners fired almost 700 radar-guided SAMs at NATO aircraft. "They were still firing SAMs on the last day of the war," said Maj. Gen. Dennis G. Haines, who was then director of combat weapons systems at Air Combat Command. Leaf had command of about 48 F-16s at Aviano. Over the course of the campaign, he said, many of his pilots "got down to last-ditch SAM maneuvering" to avoid missile shots. "I think about 20 people came very close to being shot down," Leaf said. "Most if not all were well above 15,000 feet." An A-10 flown by Short's own son was struck and dented by a SAM that somehow failed to explode. He was flying at 18,000 feet.

The criticism of Allied Force fueled an impression that there is an area of the battlespace where pilots fear to tread. Purely technical critiques of air operations have also suggested that the low-altitude region is a "lost battlespace" and that valuable targets are slipping away because of a reluctance to go down to low level. The new Secretary of the Air Force, James G. Roche, lent some credence to the case when, in June, he reportedly stated that the Air Force needed to work on regaining control of the airspace below 20,000 feet.

From the airman's point of view, the actual issue is how best to find and destroy targets efficiently. Altitude alone does not resolve the problem. Low altitude frequently has no special advantages and in most cases, flying low can degrade the capabilities of a strike aircraft.

"In a modern weapon system, there's no payoff" below 5,000 feet, Leaf explained. "In terms of precise, laser-guided bomb employment, moving it up to 15,000 or 20,000 feet, if the weather allows, you get better, not worse, in terms of precisely placing your ordnance."

As the tactical payoff diminishes, the random dangers to aircraft increase. Said Leaf: "If you are below 5,000 feet AGL, anybody with an AK-47 or anything else can really ruin your day." In Vietnam, there were several reported cases of pilots or their backseaters being killed by small-arms fire. "Above 15,000 feet, you've got less vulnerability and more reaction time," continued Leaf. "Based on radar warning or visual acquisition of something that's threatening you, you've got more time to respond and they're less likely to hit you. You don't get comfortable, but you do have a sense that above 15,000 feet you have a more significant sense of being able to control the situation."

Target acquisition is no longer the sole responsibility of the individual aircrew. Time-critical targeting that evolved during Allied Force drew on the resources of satellites, reconnaissance aircraft, UAVs, forward air controllers, airborne battle managers, and intelligence specialists processing data and tracking targets at the CAOC and other locations. Finding and killing a target is a team game; the altitude of the strike aircraft certainly is not the sole determining factor.

The transition of operations from low to medium altitude represents an evolution in the tactical flexibility of aerospace power. To Leaf, the main point was that "we didn't go to medium altitude because we had to for risk avoidance; we went to medium altitude because we had developed the capability in both airframe and associated systems and weapons to do it and still be effective."

Even so, airmen expect to come face to face with special situations in which the mission requires striking from extremely low altitude. The need to support friendly ground forces in close combat might very well be such a situation. Gen. John P. Jumper, the new Air Force Chief of Staff who was commander of US Air Forces in Europe during the Balkan air war, put it this way: "Pilots should never have to venture below the clouds unless our troops are in jeopardy. When our troops are in jeopardy, we will, but we shouldn't be going below the clouds merely to demonstrate a nobility that others accuse us of not having."

As the changing guidance in Desert Storm proved, American airmen consider it their duty to take any risk necessary to assist troops in contact with the enemy. Said Leaf, "Sometime, in extremis, when a fire team out conducting perimeter security or security operations for a battalion in combat is at risk, and has no way to respond but USAF air, then if we have to get down to 50 feet and use 20 mm then we'll do it. We'll probably take some losses, but that's war."

Changes in Attitude, Changes in Altitude Airmen have struggled with altitude questions since the dawn of air combat. Often, they decided low was best. Second Lt. H.L Borden, an observer in the 90th Aero Squadron, wrote in 1918: "For the individual observer the altitude will depend upon weather conditions, the keenness of his eyesight, concealment offered by the nature of the terrain to troops on the ground, etc." Borden found an altitude of 330 feet "most satisfactory" for demanding infantry contact missions. However, flying too low had its drawbacks. Another observer in the squadron wrote, "I found that at an altitude less than 150 meters [495 feet] it is necessary to circle over [one] point and search it thoroughly before proceeding to another, as the speed of the plane would only permit a short glance at one point." A pilot from another squadron said that, during the Meuse-Argonne offensive of 1918, "never were we allowed to fly above 600 meters [1,980 feet]"--a situation that made emergency landings treacherous. Second Lt. James E. McCurdy, 50th Aero Squadron, put it best. "Now comes the question of altitude," he wrote. "No two observers will agree on the correct altitude to fly on infantry liaison, but it is a fact that little can be accomplished at a greater altitude than 300 meters [990 feet]." McCurdy himself liked 330 to 660 feet and commented that the "machine gun fire from the ground is no worse at this altitude than at 300 meters [990 feet]." Like their World War I predecessors, World War II pilots often attacked at low altitude to achieve accuracy. P-47s strafed trains from altitudes of only 50 feet, a tactic that often resulted in losses if exploding ammunition hit the fighter itself. At Ploesti in Romania on Aug. 1, 1943, bombers flew toward the target at treetop altitude. Thirty percent of the attacking force was lost and five men received the Medal of Honor for their daring low-level attacks, the highest number in any single engagement in World War II. Close air support in World War II, Korea, and Vietnam often demanded low-altitude work. If pilots, bombardiers, and navigators had to seek the target with their own eyes to hit it, chances were they flew low.