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A-6 Intruder

History

The Navy's Korean War experience, with no jet all-weather strike capability and limited carrier air group night or all-weather effectiveness, prompted research on avionics systems to overcome this deficiency. By the mid-1950s, the Marine Corps defined its need for an all-weather close support airplane capable of operating from the shortest possible expeditionary field runways. Meanwhile, the Navy was introducing the first of a new generation of jet carrier aircraft. These ranged from the smallest attack jet -- the A4D (A-4) Skyhawk-through various fighters, to the long-range, heavy attack A3D (A-3) Skywarrior. Both of these attack types were designed for nuclear strike missions, as well as being capable of delivering conventional ordnance. However, their limitations -- including no all-weather attack systems in the A4D and the adverse impact of the A3D's large size in carrier operations -- led to studies showing that the application of new avionics technology could produce a carrier-based, all-weather attack aircraft capable of long-range conventional or nuclear strike missions flown at low terrain clearance altitudes, below radar interception. The complex avionics would require a second crewman for its effective use.

An operational requirement was established by the office of the Chief of Naval Operations in 1956 for an all-weather tactical airplane, combining the carrier attack mission with the Marines' close-support, short-field capability. Early in 1957, BUAER set forth the demanding mission and operating performance requirements, along with appropriate current design features, such as ejection seats for the aircrew. With range and short-field/carrier takeoff and landing requirements, either jet or turboprop engines would be acceptable in the design. Typically, various system components and equipment, such as the engines, would be Navy procured and furnished and the proposed contract would require the winning contractor to be responsible for the totally integrated weapon system.

Eight companies submitted 11 designs, ranging from turboprop-powered designs to a supersonic jet and a vertical/short takeoff and landing airplane. Grumman's proposal was selected in December 1957, with contract go-ahead for the now designated A2F-1 early in 1958.

The Deputy Chief of Naval Operations (Air Warfare) staff, the Bureau of Aeronautics (BUAER) personnel who prepared the type specification for the airplane's design, and the Grumman team who put together the winning proposal all played a part in creating a configuration that remained almost unchanged through 30 years of production. Extensive internal changes and replacement of the original wings with new composite construction made little difference in the basic external appearance -- once some initial design quirks were ironed out.

The adage "form follows function" is appropriate in the Intruder's case. The Grumman A-6 Intruder could never have won a beauty contest. With its engines and exhaust nozzles at mid-fuselage instead of at the rear end, an ample cockpit canopy over the crew and a bulbous radome nose, it was often described as being pointed at the wrong end. But if a warplane should sport aggressive lines, especially when carrying its lethal weapons, the Intruder measured up with a beauty all its own.

The first Intruder featured long span flaps, tilting exhaust nozzles and black speed brakes which opened into the retracted tail pipes' exhaust. A unique feature of Grumman's design that played a role in its selection was tilting exhaust nozzles on the mid-fuselage J52 engines. These exhaust outlets angled down 23 degrees for short-field or carrier take-offs and landings without producing undesirable pitching moments. Initial design and wind tunnel testing led to the mockup inspection in September 1958. Many changes in design details would follow, but the overall airframe configuration was well established.

Development and construction of initial aircraft was contracted in April 1959. The first aircraft (BuNo 147864) was rolled out in early 1960 and after ground testing at Bethpage, NY, was transported to Calverton, NY, for its first flight in April. As flight testing proceeded, various changes-several of which fortunately improved the Intruder's overall appearance-were made. The tilting exhaust nozzles didn't give enough improvement to justify their weight, complexity and cost and were eventually replaced with straight tail pipes. The vertical tail shape was changed to correct predicted marginal spin recovery characteristics, and the horizontal stabilizer was revised to a slab which was moved aft to correct a hinge moment problem without redesigning the fuselage attachment components. The speed brakes were perforated to reduce buffeting and supplemented with wing tip brakes for adequate dive-bombing effectiveness. Later, the familiar fixed centerline in-flight refueling probe in front of the windshield was added.

While airframe characteristics, including those of the new nose gear tow catapulting system, were worked out, the new avionics systems were a different story. Not only were there difficulties with individual compo-nents, but the Digital Integrated Attack and Navigation Electronics (DIANE) system was almost unworkable and the unreliability of the components was multiplied in the full system. A combined Grumman-Navy effort to redesign components gradually brought hope of a system capable of use for normal flight and led to solutions for its attack mode problems.

First used in the A2F Intruder, the Vertical Display Indicator (VDI) was a forerunner in equipment designed and adapted to fit the way a pilot functions. The VDI was a head-down cathode ray tube display which simulated real-world conditions, enabling a pilot to fly an aircraft during takeoff, navigation, attack maneuvering and landing modes as though in visual contact with his surroundings. This display technique is known as Contact Analog. The revolutionary "highway in the sky" concept was developed under the Army-Navy Instrumentation Program in response to a need for simplified cockpit instrumentation and all-weather flight capability. Kaiser Aircraft & Electronics (now Kaiser Electronics) built the first instrumentation system in the late 1950s. The original operational display presented ground and sky texture to the pilot with a well-defined horizon for attitude, "highway in the sky" for steering and numerous other symbols for execution of various attack maneuvers. In the mid-seventies heading, radar altitude, vertical speed, angle-of-attack and landing needles were added to the display. Both versions of the VDI provided ground contours for low-altitude terrain avoid-ance maneuvering while in Terrain Clearance mode.

The A2F-1 became the A-6A in 1962 designations. The A-6 carried twice the bomb load of the A-7 and was faster. It could pull 6 Gs with a full bomb load and it wouldn't rip the wings off. With its inertial navigation system, the Intruder could fly in any weather conditions, anywhere in the world and know its exact position all the time.

By early 1963, it was possible to initiate avionics Board of Inspection and Survey trials and at the same time to deliver airplanes for replacement training to Attack Squadron (VA) 42 at NAS Oceana, Va. The initial airplanes did not have fully operable avionics, but were adequate to start instructor pilot training. Initial day carrier qualifications were conducted on Forrestal (CV 59) in July. Full system airplanes began to arrive soon after and full training for both pilots and bombardier navigators (BN) began. While avionics systems reliability and maintenance continued to be a major concern, the first A-6 fleet squadron, VA-75, started its training.

Soon after VA-75 completed its training with VA-42, the events of August 1964 in the Tonkin Gulf led to the America's direct military involvement in the Vietnamese war. By spring 1965, preparations to take the new A-6s to war had progressed to the point where VA-75 deployed with Carrier Air Wing 17 on Independence (CVA 61) in May, flying its first missions against North Vietnamese targets in July. The A-6's initial combat record was anything but auspicious; the Intruder suffered problems typical of a new combat aircraft entering operational use and combat simultaneously. Premature explosion of bombs soon after release accounted for the first, and some subsequent, "combat" losses. This and the unreliability and excessive maintenance of the complex integrated avionics systems on which its all-weather bomber capability depended were tackled head on. The first was solved by fusing and wiring changes and adding multiple ejector racks on the five-store pylons. The second was more pervasive and was a continuing problem. These technical aspects led to indecision on operational mission assignments: whether to assign A-6 missions based on large bomb-carrying capability or on all-weather capabilities.

The Intruder played a critical role in the Vietnam War with over 35,000 combat sorties by 1973. The A-6 worked around the clock in Vietnam, conducting attacks on the targets with a pinpoint accuracy unavailable through any other aircraft at that time. In Vietnam, a lot of missions at night were truck hunting with F-4s. The Intruder would locate a truck using the Airborne Moving Target Indicator -- equipment unique to the A-6 which sensed movement on the ground. The A-6 would drop a flare over a target and the F-4s would then roll in and bomb. Another thing the A-6's equipment allowed was flying in between hills, at night, in fog. The A-6 Intruder's arrival in the fleet began a new era in Naval Aviation. The US Navy had achieved a remarkable ability to "hit the enemy deep in his homeland" in all kinds of weather, day or night.

Over the next several years, as subsequent A-6 squadrons rotated through Seventh Fleet duty, both the technical and operational problems reached resolution. Changes were made to various DIANE components, and successful missions in monsoon season weather dispelled planning for follow-on models with reduced avionics systems capabilities. With less emphasis on close support dive-bombing, the fuselage dive brakes were disabled and locked closed, finally being replaced in production by plain skin.

Other special-purpose versions, with systems optimized for surface-to-air missile site attacks with Standard anti-radiation missiles and for around-the-clock attacks against traffic on the Ho Chi Minh Trail, were built in smaller numbers -- 19 A-6Bs and 12 A-6Cs, respectively. These were integrated into regular A-6 squadrons.



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