Editing Grumman A-6 Intruder (section)

==Development==
===Background===
As a result of the fair-weather limitation of the [[Propeller (aircraft)|propeller-driven]] [[Douglas A-1 Skyraider|A-1 Skyraider]] in the [[Korean War]] and the advent of turbine engines, the [[United States Navy]] issued preliminary requirements in 1955 for an all-weather [[aircraft carrier|carrier-based]] [[attack aircraft]]. The U.S. Navy published an Operational Requirements Document (ORD) for it in October 1956. It released a [[Request For Proposal]]s (RFP) in February 1957.<ref>Jenkins 2002, pp. 5–6.</ref> The RFP called for a 'close air support attack bomber capable of hitting the enemy at any time'. The specification was shaped by the service's Korean War experiences, during which air support had been frequently unavailable unless fair weather conditions were present.<ref name = "bomber 209">Gunston and Gilchrist 1993, p. 209.</ref>

In response to the RFP, a total of eleven design proposals were submitted by eight different companies, including [[Bell Helicopter|Bell]], [[Boeing]], [[Douglas Aircraft Company|Douglas]], [[Grumman]], [[Lockheed Corporation|Lockheed]], [[Glenn L. Martin Company|Martin]], [[North American Aviation|North American]], and [[Vought]].<ref>Jenkins 2002, pp. 6–7.</ref> Grumman's submission was internally designated as the ''Type G-128''.<ref name = "bomber 209"/> Following evaluation of the bids, the U.S. Navy announced the selection of Grumman on 2 January 1958. The company was awarded a contract for the development of their submission, which had been re-designated ''A2F-1'', in February 1958.<ref>Jenkins 2002, p. 7.</ref>

[[File:YA2F-1 tilting pipes NAN6-60.jpg|thumb|right|250px|YA2F-1 showing the original tilting tailpipes]]
Grumman's design team was led by Robert Nafis and Lawrence Mead, Jr.<ref name = "bomber 209"/> Mead later played a lead role in the design of the [[Lunar Excursion Module]] and the [[Grumman F-14 Tomcat]].<ref>[https://www.nytimes.com/2012/08/31/business/lawrence-mead-jr-aerospace-engineer-who-helped-design-a-6-bomber-dies-at-94.html?ref=science "Lawrence Mead Jr., Aerospace Engineer, Dies at 94."] ''The New York Times'', 30 August 2012.</ref> The team was spread between two sites, the company's manufacturing plant at [[Bethpage, New York]], and the testing facilities at [[Naval Weapons Industrial Reserve Plant, Calverton]] in [[Riverhead, New York]]. During September 1959, the design was approved by the Mock-Up Review Board.<ref name = "bomber 209"/>

The A2F-1 design incorporated several cutting-edge features for the era. In the early 1960s, it was novel for a fighter-sized aircraft to have sophisticated avionics that used multiple computers. This design experience was taken into consideration by NASA in their November 1962 decision to choose Grumman over other companies like General Dynamics-Convair (the [[F-111]] had computerized avionics capabilities comparable to the A-6, but did not fly until 1964) to build the Lunar Excursion Module, which was a small-sized spacecraft with two onboard computers.{{citation needed|date=August 2011}}

===Test program===
The first prototype YA2F-1, lacking radar and the navigational and attack avionics, made its first flight on 19 April 1960,<ref>Jenkins 2002, p. 11.</ref><ref name="wapj12 p40">Dorr ''World Air Power Journal'' Spring 1993, p. 40.</ref> with the second prototype flying on 28 July 1960.<ref name="wapj12 p41">Dorr ''World Air Power Journal'' Spring 1993, p. 41.</ref>

The test program required to develop the aircraft was prolonged. The very advanced navigation and attack equipment required substantial development, and changes had to be made to correct aerodynamic deficiencies and remove unwanted features.<ref>Francillon 1990, p. 431.</ref> Extending the [[Air brake (aeronautics)|air brakes]], which were mounted on the rear fuselage, changed the downwash at the horizontal [[tailplane]] which overloaded its actuator so the tailplane was moved rearwards by {{convert|16|in|cm}}. Later evaluation of the aircraft showed that the airbrakes were not effective enough in controlling the speed of the aircraft and they were moved to the wing-tips.<ref>https://archive.org/details/202417484a6intruder/page/n5/mode/2up, p.5</ref> Early production aircraft were fitted with both the fuselage and wingtip air brakes, although the fuselage-mounted ones were soon disabled, and were removed from later aircraft.<ref name="wapj12 p41"/> 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 rudder needed a wider chord at its base to give greater exposed area to assist spin recovery.{{citation needed|date=February 2025}}

A major difference between the first six production aircraft and subsequent aircraft were the jet nozzles; the close-air support role sought by the U.S. Marine Corps required STOL performance to operate from forward airstrips. Jet deflection using tilting tailpipes was proposed. The performance benefits from varying the angle were not worthwhile, whether operating from short strips or carriers, thus they were fixed at a seven degree downward angle.<ref>Gunston 1974, p. 225.</ref>

===Further development===
During February 1963, the A-6 was introduced to service with the US Navy; at this point, the type was, according to Gunston and Gilchrist, "the first genuinely all-weather attack bomber in history".<ref name = "bomber 210">Gunston and Gilchrist 1993, p. 210.</ref> However, early operating experiences found the aircraft to be imposing very high maintenance demands, particularly in the Asian theatre of operations, and serviceability figures were also low. In response, the Naval Avionics Lab launched a substantial and lengthy program to improve both the reliability and performance of the A-6's avionics suite.<ref name = "bomber 210"/> The successful performance of the A-6 in operations following these improvements ended proposals to produce follow-on models that featured downgraded avionics.<ref name="Andrews">{{cite magazine |last=Andrews |first=Hal |title=Life of the Intruder |magazine=Naval Aviation News |volume=79 |issue=6 |date=September–October 1997 |pages=8–16}}</ref>

Various specialized variants of the A-6 were developed, often in response to urgent military requirements raised during the [[Vietnam War]].<ref name = "bomber 21011"/> The ''A-6C'', a dedicated interdictor, was one such model, as was the ''KA-6D'', a [[Aerial refueling#Buddy store|buddy store]]-equipped aerial refueling tanker. Perhaps the most complex variant was the [[EA-6B Prowler]], a specialized [[electronic warfare]] derivative. The last variant to be produced was the ''A-6E'', first introduced in 1972; it features extensive avionics improvements, including the new [[AN/APG-76#AN/APQ-148|APQ-148]] multimode radar, along with minor airframe refinements.<ref name = "bomber 21011">Gunston and Gilchrist 1993, pp. 210-211.</ref> The last A-6E was delivered in 1992.<ref>{{cite web |url = https://www.flightglobal.com/northrop-grumman/4209.article |title = Northrop Grumman |publisher = Flight International |date = 23 October 1996}}</ref>

In the early 1980s, the Navy anticipated that an Advanced Carrier-Borne Multirole Fighter (VFMX) would eventually be the long term high-end replacement for both the F-14 and A-6, although this program was short-lived and was succeeded by separate efforts for fleet air defense and deep strike/attack; the latter became the Advanced Tactical Aircraft (ATA) program resulting in the development of the [[McDonnell Douglas A-12 Avenger II]].<ref>{{cite report |last1=Parker Jr. |first1=James F |last2=Christensen |first2=Diane G. |last3=Mutimer |first3=George R. |url=https://apps.dtic.mil/sti/tr/pdf/ADA177469.pdf |title=Life Support and Protection Requirements for the Head/Neck Region of Navy Aircrewmen |date=December 1986 |publisher=Office of Naval Research |page=7}}</ref><ref>{{cite book |last=Larrimer |first=Bruce I. |title=Think Obliquely: Robert T. Jones, the Oblique Wing, NASA's AD-1 Demonstrator, and Its Legacy |url=https://www.nasa.gov/wp-content/uploads/2015/04/ThinkingObliquely-ebook.pdf |publisher=National Aeronautics and Space Administration (NASA) |location= |year=2013 |isbn=978-1-62683-005-9 |page=144}}</ref> Meanwhile, a further model, designated ''A-6F'', was being planned. Intended to feature the [[General Electric F404]] [[turbofan]] engine, as well as various avionics and airframe improvements, this variant was cancelled under the presumption that the A-12 would be entering production before long.<ref name = "bomber 211">Gunston and Gilchrist 1993, p. 211.</ref><ref name = "flyint 2011">{{cite web |url = https://www.flightglobal.com/us-naval-aviation-back-on-the-rise/99159.article |title = US naval aviation back on the rise |publisher = Flight International |first = Stephen |last = Trimble |date = 4 April 2011}}</ref> Instead, a life-extension program involving the re-winging of existing A-6E aircraft was undertaken; initially a metal wing had been used before a [[graphite]]-[[epoxy]] [[composite material|composite]] wing was developed during the late 1980s.<ref name = "bomber 21112">Gunston and Gilchrist 1993, pp. 211-212.</ref> Other improvements were introduced to the fleet around this time, including [[GPS]] receivers, new computers and radar sets, more efficient J-52-409 engines, as well as increased compatibility with various additional missiles.<ref name = "bomber 212">Gunston and Gilchrist 1993, p. 212.</ref>