The Air Defense branch is responsible for the defense against enemy aircraft and ballistic missiles. Small teams with shoulder-held anti-air missiles are attached to infantry, armor, and field artillery units and share most of their hosts' stress environments. Teams with "high-tech," mobile missiles and ultra-rapidfire guns, supported by mobile radar teams, are deployed to protect key targets such as the brigade and division support areas and corps base defense clusters. Larger missiles such as the Patriot are used to protect key air bases and ports throughout the theater of operations against ballistic missiles and long-range aircraft.
Unlike the field artillery, which are rarely totally idle, most air defense artillery in recent wars have had to sustain vigilance with little or no opportunity to fire; the exception was the Patriot missile units in the Iraq wars, deployed both in Saudi Arabia and Israel. There, the political impact of their presence far outweighed their actual (subsequently determined) performance, and placed upon them a heavy burden of responsibility. Fatigue and stress became a significant factor for those crews.
The deployment of Patriot batteries to South Korea in 1993 as a show of resolve suggested that the responsibility will continue, and become even heavier if a potential opponent is known to have chemical, biological, or nuclear warheads.
The defense of the field army, and especially the most forward of all combat troops, the maneuver divisions, had been under discussion for many decades. Its genesis was in the interwar Coast Artillery Corps, which had successfully defended the United States against sea attack since 1907. The Coast Artillery's stepchild, the Antiaircraft Artillery, gave the branch a tactical mission and the Coast Artillery spent the 1920's and 1930's in a resource-constrained environment searching for a solution. But prejudices and unproved expectations relegated the antiaircraft to employment in the corps rear until the late 1930's, when the War Department recognized the requirement to improve the AAA protection for its divisions and corps. The Antiaircraft Artillery doctrine, tactics, technology, and structure introduced between 1939 and the Battle of Kasserine Pass reflected the Coast Artillery mentality and the indifference of the US Army towards air attack in the combat zone.
During World War I, the American Army countered German low-altitude attacks against the Allied front lines and higher-altitude bombings of major industrial and urban centers with a composite force of borrowed French 75mm guns, machine guns that were modified for the antiaircraft role, and search lights. This embryonic antiaircraft force defended key points along the trench lines and critical facilities in the rear areas.
In 1923, the Coast Artillery organized the Antiaircraft Artillery battalions into two-battalion regiments to provide a complete capability against both low- and high-altitude air attack. The first battalion had the somewhat immobile 3-inch AAA gun, developed in America during World War I, but never shipped overseas. The antiaircraft gun battalion had four batteries with three guns each and a battery of searchlights. The second battalion was termed the automatic weapons battalion, although it was equipped with the single barreled .30- or .50-caliber machine gun mounted on the AAA pedestal.
In 1925, the Coast Artillery conducted a study to determine the Antiaircraft Artillery requirements for the defense of the field army. The study concluded that the antiaircraft defended two categories of targets: key transportation and logistical facilities in the rear areas and forward combat units. Since the threat to the corps and army rear areas was the bomber, guns were allocated to the defense. Specifically, in a typical corps area, four 3-inch AAA gun batteries (one regiment) could defend all the vital facilities in the corps rear, and their overlapping coverage created an area defense over the entire corps rear area and parts of the divisional rear areas.
The 3-inch AAA gun could fire a projectile over 15,000 yards, but its effective range was reduced to less than 5,000 yards due to the crude state of the weapon's fire control. An area defense required accuracy, and the improvement of fire control (a technical and complicated problem) became an obsession with the Coast Artillery. The speed of the airplane doubled between 1920 and 1939, but the Coast Artillery was unable to develop fire control devices that kept pace. These technical difficulties made the 3-inch AAA gun obsolescent by 1933.
In 1937, the appropriations for the Coast Artillery increased 12 times over the yearly average for the previous 17 years. The AAA gun remained the cornerstone of the antiaircraft force and most of the budgetary increases went toward the development and standardization of a new big gun, the 90mm, which had more range and a radar to improve its target acquisition. The 90mm gun, M1, was approved for production on 21 March 1940. The M1 was a great improvement over the 3-inch AAA gun, as it fired to an altitude of 39,000 feet. The gun was designed for use an an antiaircraft weapon. Its carriage had two road wheels that had to be folded back, and outriggers emplaced, before firing. The gun could not be depressed below zero degrees elevation, and because of the awkward carriage, without crew initiative, it was not an outstanding antitank weapon.
In April, 1941, General George C. Marshall, the Chief of Staff of the United States Army, sent a memo to the Operations Division of the Army Staff directing them to study the creation of "mobile antitank and antiaircraft units organized at the corps and army echelons" to counter the German blitzkrieg. Marshall wanted a combined arms force which was capable of rapid movement and aggressive offensive tactics. For an American Army that was still attempting to escape from the doctrinal lessons of World War I, it was a tall order. The Antiaircraft Artillery role had to be significant, for in Poland and France, the Luftwaffe made a fundamental contribution to the blitzkrieg's successes.
Since the antiaircraft guns of the time could not engage targets below 5,000 feet, the defense against the low-altitude fighter fell upon the single-barreled .30- and .50-caliber antiaircraft machine guns, first developed during World War I. Optimistically, these AAA machine guns had an effective range of 1,500 yards, so it required almost 100 systems to cover a 20-mile route of march. To an American Army intent on keeping the size of the division as small as possible, adding that much force structure to the division was not acceptable.
The 90mm gun, M2, was standardized in May 1943. It had four road wheels and could be fired from the travel configuration. Fielded in 1940, the 90mm gun's capabilities would not be tested until the Battle of Kasserine Pass.24 Pessimistic coast artillerymen expected the 90mm to provide an improved defense for point targets in the corps rear; optimists hoped for an overwatch for at least a portion of the corps area.
Perhaps the greatest lesson of World War II is that air defenders must be realistic about their capabilities in the forward area. In a branch of the Army that, by necessity, remains highly technical, there is a temptation to equate the template of a missile engagement zone with reality. History has proven that this approach does not work. Air defenders need to be tactically conservative, and they need to concentrate command and control while remaining flexible in combat. Defeating an enemy air threat from the ground requires special soldiers -- and the antiaircraft artillerymen of World War II were certainly extraordinary.
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