The Grumman A2F (A-6) Intruder was the result of a February 1957 Navy request for proposals for a replacement for the Douglas AD Skyraider in both the Navy and the Marine Corps. The request was accompanied by Type Specification 149, which asked for a two-seat aircraft capable of performing in all-weather conditions. An ability to take off and land in short distances was required, as was a top speed of at least 500 knots and a mission radius of at least 300 nautical miles. The Type Specification did not specify how many engines were to be used, or, indeed, even the type of engines to be used. Presumably either jet- or turboprop-powered designs would be acceptable.
Eight aircraft manufactures (Boeing, Douglas, Bell, Lockheed, North American, Vought, Martin, and Grumman) submitted proposals by the deadline of August 17, 1957.
During its design process, Grumman considered several different configurations, including a turboprop-powered straight-winged aircraft with twin fins and rudders as well as a pure jet-powered aircraft with turbojets mounted in pods underneath M-shaped wings, with forward swept inboard panels and swept-back outward panels. The design that they finally settled on (named Design 128Q by the company) was a two-seat jet-powered aircraft.
Since supersonic performance was not called for, the aircraft was powered by a pair of non-afterburning Pratt & Whitney J52 turbojets mounted on the lower corners of the central part of the fuselage, fed by large intakes mounted on the lower sides of the forward fuselage. Since the aircraft was strictly subsonic, complex variable-geometry intakes were not required, and the intakes were simple D-shaped inlets with a small, fixed splitter plate to separate out the fuselage boundary layer air. An unusual feature was the use of a set of extended jet exhaust pipes which could be tilted downward by 23 degrees in order to improve the STOL performance. A pair of speed brakes was installed on the lower rear fuselage, just aft of the engine exhausts.
A large-area mid-mounted wing of moderate sweep (25 degrees at quarter-chord) was provided. The wing had trailing-edge flaps that extended over almost the entire length of the wing, so conventional ailerons were not fitted. Lateral controls was provided at low speeds by the movements of the flaps (operating as "flaperons") and at high speeds by a series of spoilers mounted on the upper wing surface. The spoilers could be operated differentially for roll control in flight. The wing could be folded via a hinge at approximately 1/3 span for storage aboard carriers. The offensive load was carried aboard external pylons, two under each inner-wing panel and one underneath the fuselage centerline.
The main landing gear members were attached to the rear wing spar, just outboard of the fuselage. The members retracted forward and rotated through 90 degrees so that the wheels could lie flat in wheels in the leading edge of the wing. The nose gear retracted rearward into a well underneath the cockpit.
The horizontal stabilizer was of the all-flying variety, with two sets of gearings to define control authority. In flight the stabilizer was restricted in travel so as to not to overstress the aircraft, but this could be overridden in an emergency, such as a spin.
The two crew members sat side-by-side on ejector seats in staggered positions (the pilot was a few inches forward of the navigator/bombardier) underneath a bulbous canopy which slid to the rear as a unit for entry and exit. There were integral fold-down steps on the sides of the air intakes for crew entry and exit. A bulbous nose was provided for a large radar set. The offensive load was to be mounted entirely externally, suspended underneath underwing pylons. There was no provision for cannon armament.
Perhaps the most advanced feature of the Grumman design was the use of a new and advanced all-weather electronic system, named Digital Integrated Attack Navigation Equipment (DIANE). This advanced system had as it basis a pair of antennas in the large radome, one for a Norden AN/APQ-92 search radar, and the other for a Naval Avionics Facility AN/APQ-112 track radar. Also included was an AN/ASN-31 inertial navigation system, a CP-729A air data computer, a Litton AN/APQ-61 ballistics computer, an AN/AVA-1 vertical display, an AN/APN-141 radar altimeter, an AN/ASQ-57 integrated electronics control, and an AN/APN-153 Doppler navigation system. Also included was an Automatic Direction Finder (ADF) as well as Tactical Air Navigation (TACAN) and Identification Friend or Foe (IFF) systems.
Boeing, Douglas, Vought, and Martin submitted two designs each, one turbojet and one turboprop. Bell, Lockheed, and North American submitted just one design each. Bell's design was STOL, and was quickly dropped. Turboprop and single-engined entries were ruled out at a fairly early stage, leaving Douglas, Vought, and Grumman as the three finalists. On January 2, 1958, the Navy announced that the Grumman Design 128Q was the winner of the contest.
An initial design contract was issued on February 21, 1958 which called for preliminary design work and for a full-scale mockup. The mockup was inspected in September of 1958 and some changes were recommended. These included the straightening of the wing trailing edge and in increase in wingspan by two feet. Modified single-slotted flaps were substituted for the originally-proposed double-slotted flaps. The nose was enlarged to make it possible to incorporate both the search and track radar antennae underneath a single radome. The canopy was recontoured to reduce drag. The fin was made larger and was moved further aft. A nosewheel catapult system was adopted. The internal fuel capacity was increased by 155 gallons.
Four A2F-1 development aircraft (BuNos 147864/147867) were ordered in March of 1959. Four more (BuNos 148615/148618) were ordered in 1960.
The first example (BuNo 147864), powered by a pair of YJ52-P-6 engines, was rolled out at Bethpage on April 14, 1960. It carried no radar, and was equipped with only enough electronic equipment to allow for safe flight. After some taxiing trials, the plane was trucked out to Calverton for flight tests. The aircraft took off on its maiden flight on April 19, 1960, with test pilot Robert Smyth at the controls. The second A2F-1 (BuNo 147865) took off on its maiden flight on July 28, 1960. It also lacked radar.
Very early on in the flight test program, there were problems with the aft-mounted fuselage speed brakes. These brakes had perforations that were designed to smooth out airflow and prevent buffeting of the tail surfaces. However, early flight tests uncovered handling problems and airflow disruption caused by extension of these speed brakes. On the third airframe (BuNo 147866) the horizontal stabilizer was moved 16 inches further aft to try and correct this problem. Unfortunately, the handling problems when the speed brakes were extended still persisted, and the fuselage-mounted speed brakes were gradually replaced by unconventional wingtip-mounted speed brakes. These consisted of split hinges which extended both up and down at the wing trailing edges. The wingtip brakes were interlocked to prevent asymmetric extension. They were tested on the first A2F-1 in September of 1961. Some early A-6As were fitted with both fuselage and wingtip speed brakes, either or both of which could be selected by the pilot. Both could be used in a dive, but only the wingtip brakes could be employed during landing. Eventually, the Navy decided to standardize on the wingtip brakes, and some of the fuselage airbrake panels on the earlier A-6As were welded shut. On later aircraft, the fuselage airbrake location was faired over, but the internal structure still had an unused speed brake well present. Beginning with the 304th aircraft (BuNo 154170) the fuselage-mounted speed brakes were completely omitted. Those of earlier aircraft were rendered inoperative.
Flight tests also revealed that the tilting exhaust pipes were not very effective in reducing the takeoff distance, unless the aircraft was operating at fairly low gross weights. Consequently, tilting pipes were installed only on the first four aircraft, and provision for their installation was retained only for the next four planes. All of the production Intruders had fixed exhaust pipes. The tailpipes are skewed slightly outwards and down in order to prevent jet exhaust from reaching the horizontal stabilizer.
The fourth aircraft (BuNo 147867) was the first airplane to be fitted with the full set of avionics. It began flying in December of 1960. As expected for such a complex system, the DIANE system had lots of teething troubles and was initially quite unreliable. Initial assignment to the fleet was delayed by almost a year while the problems with the DIANE system were identified and fixed.
While the problems with the DIANE system were being worked on, carrier trials began aboard the USS Enterprise in December of 1962. Initial deliveries to the training squadron VA-42 at NAS Oceana in Virginia began in February of 1963.
On September 18, 1962, the A2F-1 was redesignated A-6A.
Most A-6As were fitted with a non-retractable refuelling probe, mounted immediately in front of the cockpit.
A total of 488 A-6As (including the prototypes) were built before production switched over to the A-6E version in December of 1970. 19 A-6As were converted to A-6Bs, 12 were converted to A-6Cs, 90 became KA-6D tankers, and 13 were converted to EA-6As. About half of the A-6As (240 in all) were later upgraded to A-6E format.
Engines: Two Pratt & Whitney J52-P-6A non-afterburning turbojets, 8500 lb.s.t. each. Performance: Maximum speed 646 mph at sea level, 555 mph at 35, 900 feet. Cruising speed 481 mph. Stalling speed 133 mph. Combat ceiling 40,250 feet. Initial climb rate 6950 feet/min. Normal range 1350 miles. Maximum ferry range 3225 miles. Weights: 25,300 pounds empty, 48,050 pounds gross, 53,700 pounds maximum. Dimensions: Wingspan 53 feet 0 inches, length 54 feet 9 inches, height 16 feet 2 inches, wing area 529 square feet. Armament: No cannon armament. A maximum weapons load of 15,000 pounds could be carried on four underwing hardpoints and one centerline hardpoint.
147864/147867 Grumman YA2F-1 Intruder (4) Redesignated A-6A in 1962. 148615/148618 Grumman YA2F-1 Intruder (4) Redesignated A-6A in 1962. 148615 converted to EA-6B electronic test aircraft. 148618 converted as EA-6A prototype. 148619/148626 Grumman A2F-1 Intruder contract cancelled. 149475/149486 Grumman A-6A Intruder (12) 149479 converted to EA-6B second development aircraft. 149481 converted to EA-6B aerodynamic demonstrator 149482, 149484, 149485, 149486 modified as KA-6D tanker. 149475, 149477, 149478 converted to EA-6A 149935/149958 Grumman A-6A Intruder (24) 149935 modified to YEA-6A prototype 149936, 149937, 144940, 144942, 144945, 149951, 149952, 149954 modified as KA-6D tanker. 149944, 149949, 149955, 149957 modified as A-6B defense suppression aircraft. 149948/149950, 149953, 149955/149957 brought up to A-6E standards. 149935 converted to NEA-6A 151558/151612 Grumman A2F-1 Intruder (43) Redesignated A-6A in 1962. 151601/151612 cancelled. 151566, 151568, 151570, 151572, 151575, 151576, 151579/151583, 151589 modified as KA-6D tanker. 151558/151565, 151591 modified as A-6B defense suppression aircraft. 151558, 151562, 151564, 151565, 151573, 151591/151593 brought up to A-6E standards. 151595/151600 converted to EA-6A 151780/151827 Grumman A-6A Intruder (48) 151783, 151787, 151789, 151791/151793, 151795, 151796, 151801, 151806, 151808/151810, 151813, 151814, 151818, 151819, 151821, 151823/151827 converted as KA-6D tanker. 151820 modified as A-6B defense suppression aircraft. 151782, 151784, 151790, 151802, 151804, 151807, 151811/151812, 151814, 151820 brought up to A-6E standards. 152583/152646 Grumman A-6A Intruder (64) 152587, 152590, 152592, 152597, 152598, 152606, 152611, 152618, 152619, 152624, 152626, 152628, 152632, 152637 converted as KA-6D tanker. 152616, 152617 converted to A-6B defense suppression aircraft. 152583/152585, 152587, 152591, 152593, 152596, 152599, 152600, 152603, 152607, 152610, 152614, 152617, 152620, 152621, 153623, 152630, 153634, 152635, 152640/152642, 152645 brought up to A-6E standards. 152891/152954 Grumman A-6A Intruder (64) 152892/152894, 152896, 152906, 152910, 152911,152913, 152914, 152919/152921, 152927, 152934, 152939 converted as KA-6D tanker 152895, 152902, 152904, 152905, 152907, 152908, 152912, 152915, 152916, 152918, 152923/152925, 152928/152931, 152933, 152935, 152936, 152941, 152943, 152945, 152947, 152948, 152950, 152953, 152954 brought up to A-6E standards. 154124/154171 Grumman A-6A Intruder (48) 154133, 154147, 154154 converted as KA-6D tanker 154124, 154126, 154128, 154129, 154131, 154132, 154134/154137, 154140, 154142, 154144, 154146, 154148, 154151, 154154, 154156, 154158, 154159,154161/154163, 154167/154171 brought up to A-6E standards. 155581/155721 Grumman A-6A Intruder (141) 155673 modified as development aircraft for A-6E later returned to A-6A configuration, but was again modified as A-6E. 155582/155584, 155588, 155597, 155598, 155604,155619, 155638, 155686, and 155691 converted as KA-6D tanker. 155628/155630 modified as A-6B defense suppression aircraft. 155647, 155648, 155653, 155660, 155662, 155667, 155670, 155674, 155676, 155689, 155684, 155688 converted to A-6C night interdiction aircraft. Most A-6Cs later brought up to A-6E standards. 155581/155586, 155588/155592, 155595/155600, 155602, 155604, 155606, 155608, 155610, 155612, 155615/155617, 155619/155621, 155623/155625, 155627/155633, 155625/155638, 155642/155646, 155648, 155649, 155651, 155653/155662, 155664, 155665, 155667/155670, 155672/155676, 155678/155685, 155687/155689, 155692, 155694, 155695, 155697/155699, 155702/155704, 155706/155708, 155710/155719 brought up to A-6E standards. 156994/157029 Grumman A-6A Intruder (36) 156995/156997, 157000/157006, 157009/157014, 157016, 157017, 157019, 157021, 157023/157027, and 157029 brought up to A-6E standards.