The Air Domain and the Challenges of Modern Air Warfare Harry Foster t is difficult to imagine a modern world with- • Allowed rapid insertion and resupply of Iout flight and its associated technologies. The forces at great distance from supporting speed possible in the air domain shrinks time: bases; and A modern airliner travels 25 times faster than the fastest cruise ship on the Atlantic and seven • Allowed air forces to go “over not times faster than the fastest locomotive in the through” the front lines of opposing 1950s. Militarily, operating in the air domain armies, disrupting rearward logistics, de- provides vantage: the ability to see not only over nying maneuver, and taking war directly the next hill, but also over the horizon. It pro- to capitals. vides maneuverability unencumbered by moun- tain ranges, roads, river crossings, or rocky Today, from a military perspective, the de- shoals at sea. Although navalists frequently re- gree to which the United States can exploit the mind us that 70 percent of the world is covered air domain in its favor to find and hold at risk by oceans, 100 percent of the world is covered by any target (fixed, mobile, hardened, and deep air. The air domain is physically linked to every inland) anywhere on the globe is a key differ- other domain, thus providing flexibility in op- entiator that makes it a military superpower. erations, while its range provides an avenue for Understanding the complexity of modern access anywhere in the world, anytime. air power begins with a basic understanding of Over the past century, exploitation of the the air domain itself. This means understand- air domain’s speed, vantage, maneuverability, ing the air domain’s unique attributes; how flexibility, and range changed the nature of one can access and use the domain while ex- warfare. Specifically, it: ploring the limits of height and speed for plat- forms that operate in it; the domain’s unique • Created new asymmetries that broke the attributes of speed, range, persistence, and stalemate of trench warfare after World payload that have allowed the United States to War I, enabling combined-arms maneuver dominate conflicts for the past 25 years; and warfare that is with us today; current key shifts in the domain, driven by the evolution of technology and the return of state- • Extended the reach of fleets and shore based competition, and their implications for defenses beyond the sight of observation future military requirements. towers or the range of naval surface fires, making control of the air a requisite for operations on the sea; The Heritage Foundation | heritage.org/Military 59 Attributes of the Air Domain per hour from the west at 35,000 feet over The Atmosphere: Home to the Air Do- the central United States in winter to as main. The Department of Defense defines the much as 200 miles per hour in the stron- air domain as “the atmosphere, beginning at gest jet streams. the Earth’s surface, extending to the altitude where its effects upon operations become neg- • Above the troposphere is the stratosphere, ligible.”1 At its most fundamental level, the at- which extends to about 180,000 feet. The mosphere is composed of air, a mixture of gases stratosphere is where the ozone layer is consisting of 21 percent oxygen, 78 percent located, and it is free from clouds and nitrogen, and 1 percent argon, carbon dioxide, weather. Wind diminishes significantly and other gases.2 with altitude in the stratosphere. Most of The composition of air is perhaps its most today’s military operations occur in the extraordinary and important characteristic troposphere and the stratosphere. because it determines the very nature of the domain and dictates what can and cannot be • Above the stratosphere at an altitude of done in it and drives the characteristics of the about 34 miles is a region of the atmo- platforms that fly through it. Because these sphere that has proven easy to transit gases have mass, the distribution of the at- but difficult to operate in persistently. In mosphere is not uniform. For example, due this region, there is enough air to cause to gravitational effects, nearly 50 percent of drag and surface heating but not enough atmospheric mass is contained below 18,000 to support aerodynamic control or air- feet at the equator, 90 percent is contained breathing engine combustion. below 52,000 feet, and 99.99 percent is con- tained below 330,000 feet or an altitude of 100 • Sitting above the stratosphere, extending kilometers.3 While some international organi- to 260,000 feet, is the mesosphere. Here, zations such as the Fédération Aéronautique meteors burn up due to atmospheric heat- Internationale define 100 kilometers as the ing. The ionosphere, which causes high- beginning of space, the United States does not frequency radio waves to bounce off the recognize a formal boundary either by treaty atmosphere enabling long-range amateur or by policy.4 radio operations, begins in this region. The atmosphere is divided into several lay- ers that are of varying degrees of significance • Above the mesosphere lies the final layer to military operations. of the atmosphere, the thermosphere, which extends to as much as 600 miles • The lowest level, the troposphere, varies above the Earth depending on solar activ- in height from the surface to 60,000 feet at ity. Atmospheric drag caused by gases in the equator to 30,000 feet over the poles. the lower portion of this layer limits the All weather occurs in the troposphere. lowest unpowered, stable satellite orbit to The top of the troposphere, called the roughly 120 miles. tropopause, is the “cap” where summer thunderstorms flatten out to form an anvil Accessing the Air Domain for Military shape. In the troposphere, the wind blows Advantage. From its earliest days, competi- west to east in the Northern Hemisphere tion in the air domain has been enabled by and east to west in the Southern Hemi- constantly advancing technology. Warfight- sphere. Temperature decreases by about ing in the air domain, however, is fundamen- 3.5 degrees Fahrenheit with every 1,000 tally a human endeavor, and as one learns feet of climb. Wind speed changes signifi- about airspace technologies, it is important to cantly with altitude, averaging 75 miles keep technology in perspective. Technology 60 2018 Index of U.S. Military Strength enables access to and exploitation of the air Heavier-than-air flight, on the other hand, domain, but humans marshal this technol- uses aerodynamic forces to produce and sus- ogy to gain advantage over others as a tool tain lift. Aerodynamic lift is produced by mov- of statecraft and war. Competition in the air ing an airfoil (wing) through volume of air or domain therefore centers on maintaining or fluid. Design differences between the upper denying this advantage and depends not only and lower surfaces of the airfoil force the air on mastery of technology, but also on its artful to move faster across the upper surface as the and creative organization and application in wing is propelled through the air. This creates strategy and tactics. an area of lower pressure on the top of the wing The characteristics of air and the atmo- that generates lift. There are other factors in- sphere make five modes of access to the volved, but if one produces enough aerody- air domain possible: lighter-than-air flight, namic lift to overcome the force of gravity, then heavier-than-air flight, missiles, ground-fired a heavier-than-air machine can fly.9 or sea-fired projectiles, and the electromag- There are two other forces at play in the cre- netic spectrum. ation of aerodynamic lift: the thrust required Lighter-than-air flight is achieved by trap- to propel a wing though the air to generate lift ping gases lighter than oxygen and nitrogen, and the drag that the wing creates through the like hydrogen or helium, or heated air in a process of creating lift. Thus, balancing the sealed casing. Because the gas inside the cas- problems of lift, gravity, thrust, and drag makes ing is lighter than the surrounding air, lift is flight possible using vehicles that are powered produced. The volume of air contained in that (airplanes, cruise missiles, helicopters, tilt ro- casing, coupled with the characteristics of the tors, and quad copters) and unpowered (towed gas inside, determines its lifting ability. This gliders, lifting bodies, and air-delivered guided allows exploitation of the air domain using hot- munitions). Aircraft provide a reusable form of air balloons, gas-filled balloons, or powered air- access to the air domain and offer an incredible ships (dirigibles and blimps). Lighter-than-air degree of flexibility with regard to speed, range, aircraft can provide persistence and relatively payload, and endurance for military operations. heavy lift, but this means of access is both slow Missiles use the brute force of expanding, and heavily affected by weather. burning gases provided by liquid-fueled or sol- Lighter-than-air flight was exploited in id-fueled rocket engines to overcome the effects World War I by Germany, which used dirigibles, of gravity and gain access to the air domain. As or powered airships, to bomb central London, the vehicle accelerates, it takes on aerodynamic and in World War II by the United States, characteristics and can be controlled using air- which used blimps for antisubmarine warfare craft-like control surfaces until it reaches mid- patrols.5 Although the speed of heavier-than- stratosphere. Above this altitude, small thrust- air platforms made them dominant over their ers or gimbaled engines controlled by guidance lighter-than-air brothers, a role remains for systems allow the highest levels of precision in balloons and powered airships today.