The Douglas A-4 Skyhawk is a carrier-capable attack aircraft developed for the United States Navy and United States Marine Corps. The delta winged, single-engined Skyhawk was designed and produced by Douglas Aircraft Company, and later by McDonnell Douglas. It was originally designated the A4D under the U.S. Navy's pre-1962 designation system.
The Skyhawk is a light-weight aircraft with a maximum takeoff weight of 24,500 pounds (11,100 kg) and has a top speed of more than 600 miles per hour (970 km/h). The aircraft's five hardpoints support a variety of missiles, bombs and other munitions and was capable of delivering nuclear weapons using a low altitude bombing system and a "loft" delivery technique. The A-4 was originally powered by the Wright J65 turbojet engine; from the A-4E onwards, the Pratt & Whitney J52 was used.
Skyhawks played key roles in the Vietnam War, the Yom Kippur War, and the Falklands War. Fifty years after the aircraft's first flight, some of the nearly 3,000 produced remain in service with several air arms around the world, including from the Brazilian Navy's aircraft carrier, São Paulo.
The Skyhawk was designed by Douglas Aircraft's Ed Heinemann in response to a U.S. Navy call for a jet-powered attack aircraft to replace the older Douglas AD Skyraider (later redesignated A-1 Skyraider). Heinemann opted for a design that would minimize its size, weight, and complexity. The result was an aircraft that weighed only half of the Navy's weight specification. It had a wing so compact that it did not need to be folded for carrier stowage. The diminutive Skyhawk soon received the nicknames "Scooter", "Kiddiecar", "Bantam Bomber", "Tinker Toy Bomber", and, on account of its nimble performance, "Heinemann's Hot-Rod".
The aircraft is of conventional post-World War II design, with a low-mounted delta wing, tricycle undercarriage, and a single turbojet engine in the rear fuselage, with two air intakes on the fuselage sides. The tail is of cruciform design, with the horizontal stabilizer mounted above the fuselage. Armament consisted of two 20 mm (.79 in caliber) Colt Mk 12 cannons, one in each wing root, with 200 rounds per gun, plus a large variety of bombs, rockets, and missiles carried on a hardpoint under the fuselage centerline and hardpoints under each wing (originally one per wing, later two).
The choice of a delta wing, for example, combined speed and maneuverability with a large fuel capacity and small overall size, thus not requiring folding wings, albeit at the expense of cruising efficiency. The leading edge slats were designed to drop automatically at the appropriate speed by gravity and air pressure, saving weight and space by omitting actuation motors and switches. Similarly the main undercarriage did not penetrate the main wing spar, designed so that when retracted only the wheel itself was inside the wing and the undercarriage struts were housed in a fairing below the wing. The wing structure itself could be lighter with the same overall strength and the absence of a wing folding mechanism further reduced weight. This is the opposite of what can often happen in aircraft design where a small weight increase in one area leads to a compounding increase in weight in other areas to compensate, leading to the need for more powerful, heavier engines and so on in a vicious circle.
The A-4 pioneered the concept of "buddy" air-to-air refueling. This allows the aircraft to supply others of the same type, eliminating the need of dedicated tanker aircraft—a particular advantage for small air arms or when operating in remote locations. This allows for greatly improved operational flexibility and reassurance against the loss or malfunction of tanker aircraft, though this procedure reduces the effective combat force on board the carrier. A designated supply A-4 would mount a center-mounted "buddy store", a large external fuel tank with a hose reel in the aft section and an extensible drogue refueling bucket. This aircraft was fueled up without armament and launched first. Attack aircraft would be armed to the maximum and given as much fuel as was allowable by maximum takeoff weight limits, far less than a full tank. Once airborne, they would then proceed to top off their fuel tanks from the tanker using the A-4's fixed refueling probe on the starboard side of the aircraft nose. They could then sortie with both full armament and fuel loads. While rarely used in U.S. service since the KA-3 Skywarrior tanker became available, the Boeing F/A-18E/F Super Hornet includes this capability.
The A-4 was also designed to be able to make an emergency landing, in the event of a hydraulic failure, on the two drop tanks nearly always carried by these aircraft. Such landings resulted in only minor damage to the nose of the aircraft which could be repaired in less than an hour.
The Navy issued a contract for the type on 12 June 1952, and the first prototype first flew from Edwards Air Force Base, California on 22 June 1954. Deliveries to Navy and Marine Corps squadrons (to VA-72 and VMA-224 respectively) commenced in late 1956.
The Skyhawk remained in production until 1979, with 2,960 aircraft built, including 555 two-seat trainers. The last production A-4, an A-4M issued to a Marine squadron (VMA-331) had the flags of all nations who had operated the A-4 series aircraft painted on the fuselage sides.