THE INTRUDER

During the Korean War, carrier based aircraft played a large role in ground support operations of United Nations forces, especially in the early days of the conflict. While the piston powered Douglas A-1 Skyraider provided effective ground support, it was not capable of all weather operation over the target. The United States Navy was in need of an aircraft, which could carry more ordinance to the target, as well as perform ground attack missions in all kinds of weather. The answer to this problem is the subject of this blog-the Grumman A-6 Intruder.

The Intruder was designed as the result of a 1957 requirement issued by the Bureau of Aeronautics for an all-weather attack aircraft capable of long-range interdiction missions in a naval role and with short takeoff and landing (STOL) capability for Marine close air support. The requirement allowed the use of either turboprop or jet engines for the proposed design, with eleven design proposals submitted by eight different companies to include Bell, Boeing, Douglas, Grumman, Lockheed, Martin, North American and Vought. Following evaluation of the bids, the U.S. Navy announced the selection of the Grumman proposal on January 2, 1958. The Grumman plane was powered by two Pratt & Whitney J52 turbojet engines with the initial model designated the A2F1 the following month. This design incorporated a number of high tech features for the era, such as using multiple computers-an arrangement more akin to bombers of the day. The computerized avionics on the Intruder design were so successful that NASA chose Grumman to provide avionics for the Lunar Excursion Module, which was a small spacecraft with two onboard computers. The test program for the aircraft was a long one (3 yrs.) due to the need to correct aerodynamic deficiencies and remove unwanted features. For example, the rudder needed a wider chord at its base to assist in spin recovery. Air brakes were an issue. Initially mounted on the rear fuselage and the wing-tips, their extension early in the test program changed the downwash at the horizontal tail plane, which overloaded the actuator. The Grumman designers then moved the tail plane back sixteen inches, hoping to have a better braking effect. Later tests proved moving the air brakes to the rear were not effective in controlling the speed of the aircraft and resulted in the fuselage-mounted air brakes being removed in favor of wing-tip brakes, with the trailing edge of each wing-tip split to form a much more effective speed-brake, which projected above and below the wing when extended.

The A-6 was manned by a crew of two, pilot and bombardier-navigator, seated side by side. As a convenience, the all-weather navigation and weapons delivery system provides an integrated electronic display, which allows them to view both targets and terrain features, regardless of weather conditions. Because of this, the Intruder has been used a number of times as a search plane for other types of attack aircraft, permitting their use under conditions which would not permit a successful mission. In addition to its characteristics of twin engines and all-weather capability, the Intruder was able to deliver as many as thirty different types of weapons with a maximum load of 18,000 lbs. among the five underwing pods. The Intruder had a weapons system that could be configured for a variety of missions, to include strike missions, close air support and interdiction. The A-6 has a solidly built airframe made of aluminum and steel, which allowed it to withstand the stresses of high-speed flight and heavy weapon loads. The wing of the Intruder was relatively efficient at subsonic speeds, when compared to jet fighters of the era, such as the McDonnell Douglas F-4 Phantom II, which were limited to subsonic speeds while carrying bombs. The A-6 wing allowed a relatively high level of maneuverability, even while carrying a sizable bomb load. The Intruder was also capable of carrying nuclear weapons, which would have been delivered by means of semi-automated toss bombing.

When the A-6 Intruder entered service in early 1963, it was the primary all-weather attack aircraft of both the United States Navy and Marine Corps. The A-6 was the primary attack aircraft during the Viet Nam War, flying from U.S. aircraft carriers off the Vietnamese coast. Intruders launched attacks against targets across both North and South Viet Nam during the entire war. It was supported in this role by USAF attack aircraft such as the Republic F-105 Thunderchief and modified McDonnell Douglas F-4 Phantom IIs. As a result of operations over Viet Nam, a total of 84 Intruders were lost, with 56 of those downed by anti-aircraft artillery and other ground fire. Due to the success of the A-6 as a ground attack platform, the U.S. Navy initiated plans in 1967 to convert several A-6As into A-6Bs to serve as defense suppression aircraft. This modification required the removal of many of the aircraft's attack systems in favor of specialized electronics for deploying anti-radiation missiles such as the AGM-45 Shrike and AGM-75 Standard. A night attack version, the A-6C was developed in 1970, which incorporated improved radar and ground sensors. In the early 1970's, the U.S. Navy converted a portion of the Intruder force into KA-6Ds, to meet a requirement for tanker aircraft. The KA-6Ds saw extensive service over the next twenty years, with many deployed to the Middle East during the Gulf War. The A-6E, introduced in 1970, became the dominant variant of the plane. The A-6E was equipped with the latest electronics, to include the Norden AN/APQ-148 multi-mode radar and the AN/ASN-92 inertial navigation system. Continually upgraded through the 1980's and 1990's, the A6-E proved an effective weapons carrier for such precision-guided missiles as the AGM-84 Harpoon, AGM-65 Maverick, and the AGM-88 Harm. The A6-E also incorporates a surveillance system called TRAM (Target Recognition Attack Multisensor). First used in the latter stages of the Viet Nam War, TRAM offers television-type imagery of targets not detectable by radar or visually and is coupled to laser-guided weapons. Another electronic bombing tool, which came into use about the same timeframe as TRAM, was the Digital Integrated Attack and Navigation Equipment, or DIANE. DIANE was a high tech bomb release device, which could incorporate any speed, rate of climb, angle of dive, wind or altitude and G force, and calculate the optimum time to release a payload. The digital tool's Vertical Display Indicator allowed the pilot to graphically view the horizon, terrain, sky, radar altitude, as well as angle of attack.

The Intruder continued to play an important role after Viet Nam during operations over Lebanon in 1983. A-6s were heavily involved in bombing Libya in response to Colonel Muammar Gaddafi's support of terrorist groups in the Middle East. Intruders flew support missions during the Gulf War in 1991 as part of Operation Desert Sword, with U.S. Navy and Marine Corps A-6s flying over 4,700 combat sorties. Intruders provided close ground support in Somalia in 1993, as well as in Bosnia the following year. In the mid 1990's, the Department of Defense sought to retire the plane for an aircraft which could perform both ground attack and fighter missions. Though an immediate replacement was not available, the Navy assigned F-14 Tomcat squadrons to serve in the ground attack role in addition to their fighter roles. The F-18 Super Hornet performs these missions today. The last Intruder was retired in February 1997. The relatively low A-6 losses in Viet Nam as well as the Middle East, in addition to its effectiveness in the close air support role was a tribute to the original design of the plane, the first Navy aircraft to have an integrated airframe and weapons system.