The Northrop Grumman E-2 Hawkeye is an American all-weather, carrier-capable tactical airborne early warning(AEW) aircraft. This twin-turboprop aircraft was designed and developed during the late 1950s and early 1960s by the Grumman Aircraft Company for the United States Navy as a replacement for the earlier E-1 Tracer, which was rapidly becoming obsolete. The aircraft's performance has been upgraded with the E-2B, and E-2C versions, where most of the changes were made to the radar and radio communications due to advances in electronic integrated circuits and other electronics. The fourth version of the Hawkeye is the E-2D, which first flew in 2007. The E-2 was the first aircraft designed to be an AEW aircraft from the outset, as opposed to a modification of an existing airframe, such as the E-3. Variants of the Hawkeye have been in continuous production since 1960, giving it the longest production run of any carrier based aircraft.

The E-2 also received the nickname "Super Fudd"because it replaced the E-1 Tracer "Willy Fudd". In recent decades, the E-2 has been commonly referred to as the "Hummer" because of the distinctive sounds of its turboprop engines, quite unlike that of turbojet and turbofan jet engines. The E-2 and its sister, the C-2 Greyhound, are currently the only propeller airplanes that operate from aircraft carriers. In addition to U.S. Navy service, smaller numbers of E-2s have been sold to the armed forces of Egypt, France, Israel, Japan, Mexico, Singapore andTaiwan.

Development
Background
Continual improvements in airborne radars through 1956 led to the construction of AEW airplanes by several different countries and several different armed forces. The functions of command and control and sea & air surveillance were also added. The first carrier-based aircraft to perform these missions for the U.S. Navy and its allies was the Douglas AD Skyraider, which was replaced in US Navy service by the Grumman E-1 Tracer, which was a modified version of the S-2 Tracker twin-engine anti-submarine warfare aircraft, where the radar was carried in an aerofoil-shaped radome carried above the aircraft's fuselage. The E-1 was used by the U.S. Navy from 1958 to 1977.

E-2A and E-2B Hawkeye
In 1956, the U.S. Navy developed a requirement for an airborne early warning aircraft where its data could be integrated into the Naval Tactical Data Systemaboard the Navy's ships, with a design from Grumman being selected to meet this requirement in March 1957. Its design, initially designated W2F-1, but later redesignated the E-2A Hawkeye, was the first carrier plane that had been designed from its wheels up as an AEW and command and control airplane. The problems facing the design engineers at Grumman were immense, and were compounded by having to constrain the design to enable the aircraft to operate from the older ‘modified Essex class aircraft carriers’. These ‘smaller’ carriers were built during WW2 and later modified to allow them to operate jet aircraft. Consequently, various height, weight and length restrictions had to be factored into the E-2A design, resulting in some handling characteristics which were less than ideal. The E-2A only operated from the modified Essex class for a few years before the ships were decommissioned, and it's likely the design would have benefited considerably if this requirement had never been imposed.

The first prototype, acting as an aerodynamic testbed only, flew on 21 October 1960, with the first fully equipped aircraft following on 19 April 1961, enterring service with the US Navy as the E-2A in January 1964.

By 1965 the major development problems delaying the E-2A Hawkeye got so bad that the aircraft was actually cancelled after 59 aircraft had already been built. Particular difficulties were being experienced due to inadequate cooling in the closely packed avionics compartment. Early computer and complex avionics systems generated considerable heat; without proper ventilation this would lead to system failures. These failures continued long after the aircraft entered service and at one point reliability was so bad the entire fleet of aircraft was grounded. The airframe was also prone to corrosion, a serious problem in a carrier based aircraft.

After Navy officials had been forced to explain to Congress why four production contracts had been signed before avionics testing had been completed, action was taken; Grumman and the US Navy scrambled to improve the design. The unreliable rotary drum computer was replaced by a Litton L-304 digital computer[6] and various avionics systems were replaced – the upgraded aircraft were designated E-2Bs. In total, 49 of the 59 E-2As were upgraded to E-2B standard. These aircraft replaced the E-1B Tracers in the various US Navy AEW squadrons and it was the E-2B that was to set a new standard for carrier based AEW aircraft.

E-2C Hawkeye and developments
Although the upgraded E-2B was a vast improvement on the unreliable E-2A, it was an interim measure. The US Navy knew the design had much greater capability and had yet to achieve the performance and reliability parameters set out in the original 1957 design. In April 1968 a reliability improvement program was instigated. In addition, now that the capabilities of the aircraft were starting to be realized, more were desired; 28 new E-2Cs were ordered to augment the 49 E-2Bs that would be upgraded. Improvements in the new and upgraded aircraft were concentrated in the radar and computer performance.

Two E-2A test machines were modified as prototypes of the E-2C, with the first flying on 20 January 1971. Trials proved satisfactory and the E-2C was ordered into production, with the first production machine performing its initial flight on 23 September 1972. The original E-2C, known as Group 0, consisted of 55 aircraft with the first aircraft becoming operational in 1973. They began arriving on carriers in the 1980s, serving until the 1990s when they were replaced by Group II aircraft in first-line service. Some ended up in the US Navy Reserve, being used to track drug smugglers. The type was also commonly used in conjunction with Grumman Tomcat fighters; monitoring airspace and then vectoring Tomcats over the Link-4A datalink to destroy potential threats with long rangeAIM-54-C Phoenix missiles.

The next production run, between 1988 and 1991, saw 18 aircraft built to the Group I standard. Group I aircraft replaced the E-2's older APS-125 radar and T56-A-425 turboprops with their successors, the APS-139 radar system and T56-A-427 turboprops. The first Group I aircraft entered service on August 1981. Upgrading the Group 0 aircraft to Group 1 specifications was considered, but the cost was comparable to a new production aircraft, so upgrades were not conducted.

Group 1 aircraft were only flown by the Atlantic fleet squadrons. This version of the E-2 was followed within a few years by the more-improved Group II, which had the improved APS-145 radar. Group II aircraft have been incrementally upgraded with new navigation systems, better situational display, and computerized electronics; culminating in the E-2C Hawkeye 2000 variant (sometimes called the Group III). A total of 50 Group II aircraft were delivered, 12 being upgraded Group I aircraft. This new version entered service in June 1992 and served with the Pacific and Atlantic Fleet squadrons.

By 1997 the US Navy intended that all the front line squadrons would be equipped, for a total of 75 Group II aircraft. However Grumman merged with Northrop in 1994 and plans began on the next upgrade, known as the Group II Plus, which eventually became known as the Hawkeye 2000. The Hawkeye 2000 featured the APS-145 radar with a new mission computer and CIC (Combat Information Center) workstations (Advanced Control Indicator Set or ACIS), and carries the U.S. Navy’s new CEC (cooperative engagement capability) data-link system. It is also fitted with a larger capacity vapor cycle avionics cooling system. A variant of the Group II with the upgrades to the mission computer and CIC workstations is referred to as the MCU/ACIS. All Group II aircraft have had their 1960s vintage computer-processors replaced by a mission computer with the same functionality but built using more modern computer technology. This is referred to as the GrIIM RePr (Group II Mission Computer Replacement Program, pronounced "grim reaper").
In 2004, the E-2C's propeller system was changed; a new eight-bladed propeller system named NP2000 was developed by the Hamilton-Sundstrand company to replace the old four-bladed design. Improvements included better fuel economy as a result of increased efficiency, reduced vibrations and better maintainability as a result of the ability to remove prop blades individually instead of having to remove the entire prop and hub assembly. The system had previously been used in the C-130 Hercules, which also uses the T-56 engine, to great effect. The propeller blades are of carbon fiber construction with steel leading edge inserts and de-icing boots at the root of the blade.

Starting in 2007 a hardware and software upgrade package began to be added to existing Hawkeye 2000 aircraft. This upgrade allows faster processing, double current trackfile capacity and access to satellite information networks. Hawkeye 2000 cockpits being upgraded include solid-state glass displays, modern weather detection systems and a GPS-approach capability.

E-2D Advanced Hawkeye
Though once considered for replacement by the "Common Support Aircraft", this conception never went into production, and the Hawkeye will continue in its role as the Navy's primary AEW aircraft for years into the future in the E-2D version.

The latest version of the E-2, the E-2D Advanced Hawkeye, is currently under development. The first two E-2D aircraft, "Delta One" and "Delta Two" are in flight testing and several other aircraft are currently undergoing Initial Operational Test and Evaluation with Test and Evaluation Squadron One at NAS Patuxent River. The E-2D features an entirely new avionics suite, including the new APY-9 radar, radio suite, mission computer, integrated satellite communications capability, flight management system, improved T56-A-427A turboprop engines, a new tactical glass cockpit and the potential capability for air-to-air refueling. The APY-9 radar features anActive Electronically Scanned Array, which adds electronic scanning to the mechanical rotation of the radar in its radome. The E-2D will include provisions for the copilot to act as a "Tactical 4th Operator" (T4O), who, by reconfiguring his main cockpit display to display radar, IFF, and Link 16(JTIDS)/CEC, will have access to the full range of the mission's acquired data. The E-2D's first flight occurred on 3 August 2007. On 8 May 2009, an E-2D Advanced Hawkeye used its Cooperative Engagement Capability system to engage an overland cruise missile with a Standard Missile SM-6 fired from another platform in an integrated fire-control system test.[12] Deliveries of initial production E-2Ds to Navy began in 2010.

On 4 February 2010, Delta One conducted the first E-2D carrier landing aboard the USS Harry S. Truman as a part of carrier suitability testing. On 27 September 2011, an E-2D was successfully launched by the prototype Electromagnetic Aircraft Launch System (EMALS) at Naval Air Engineering Station Lakehurst. On 12 February 2013, the Office of the Secretary of Defense approved the E-2D Hawkeye to enter full-rate production. Northrop had delivered 9 E-2Ds to the U.S. Navy, with 11 more in various stages of manufacturing and pre-delivery flight-testing. The Navy plans for an initial operational capability by 2015. With the Navy's E-2D program of record at 75 aircraft, the decision enables the production of the remaining 55 aircraft over the next 10 years.[17] In June 2013, the 10th E-2D was delivered to the Navy, with an additional 10 aircraft in various stages of manufacturing and predelivery flight testing. On 18 July 2013, Northrop Grumman was awarded a $113.7 million contract for five full-rate production Lot 2 E-2D Advanced Hawkeye aircraft. Total current procurement of E-2D aircraft, including low-rate initial production and full-rate production aircraft, is for 30 planes. On 13 August 2013, Northrop Grumman was awarded a $617 million contract for five E-2D Advanced Hawkeyes until full-rate production Lot 1.

Design
The E-2 is a high-wing airplane, with one turboprop engine in each wing, and retractable tricycle landing gear. As with most carrier-borne airplanes, the E-2 is equipped with a tail hook for landings, and it is capable of using the aircraft carrier's catapults for take-off. A distinguishing feature of the Hawkeye is its 24-foot (7.3 m) diameter rotating dome that is mounted above its fuselage and wings. This carries the E-2's primary antennas for its long-range radar and IFFsystems. No other carrier-borne aircraft possesses one of these, and among land-based aircraft, they are mostly seen atop the Boeing E-3 Sentry, a larger AWACSairplane operated by the U.S. Air Force and NATO air forces in large numbers.

The aircraft is operated by a crew of five, with the pilot and co-pilot on the flight deck and the combat information center officer, air control officer and radar operator stations located in the rear fuselage directly beneath the rotodome.

In U.S. service, the E-2 Hawkeye provides all-weather airborne early warning and command and control capabilities for all aircraft-carrier battle groups. In addition, its other purposes include sea and land surveillance, the control of the aircraft carrier's fighter planes for air defense, the control of strike aircraft on offensive missions, the control of search and rescue missions for naval aviators and sailors lost at sea, and for the relay of radio communications, air-to-air and ship-to-air. It can also serve in an air traffic control capacity in emergency situations when land-based ATC is unavailable.

The E-2C and E-2D Hawkeyes use advanced electronic sensors combined with digital computerized signal processing, especially its radars, for early warning of enemy aircraft attacks and anti-ship missile attacks, and the control of the carrier's combat air patrol (CAP) fighters, and secondarily for surveillance of the surrounding sea and land for enemy warships and guided-missile launchers, and any other electronic surveillance missions as directed.

Operational history
US Navy
The E-2A entered U.S. Navy service on January 1964, and in April 1964 with VAW-11 at NAS North Island.[5] The first deployment was aboard the USS Kitty Hawk (CVA-63) during 1965.

Since entering combat during the Vietnam War, the E-2 has served the US Navy around the world, acting as the electronic "eyes of the fleet". In August 1981, a Hawkeye from VAW-124 "Bear Aces" directed two F-14 Tomcats from VF-41 "Black Aces" in an intercept mission in the Gulf of Sidra that resulted in the downing of two Libyan SU-22 Fitters. Hawkeyes from VAW-123 aboard the aircraft carrier USS America (CV-66) directed a group of F-14 Tomcat fighters flying the Combat Air Patrol duringOperation El Dorado Canyon, the joint strike of two Carrier Battle Groups in the Mediterranean Sea against Libyan terrorist targets during 1986. More recently, E-2Cs provided the command and control for both aerial warfare and land-attack missions during the Persian Gulf War. Hawkeyes have supported the U.S. Coast Guard, the U.S. Customs Service, and American federal and state police forces during anti-drug operations.

In the mid-1980s, several E-2Cs were borrowed from the U.S. Navy and given to the U.S. Coast Guard and the U.S. Customs Service for counternarcotics (CN) and maritime interdiction operations (MIO). This also led to the Coast Guard building a small cadre of Naval Flight Officers (NFOs), starting with the recruitment and interservice transfer of Navy flight officers with E-2 flight experience and the flight training of other junior Coast Guard officers as NFOs. A fatal aircraft mishap on 24 August 1990 involving a Coast Guard E-2C at the former Naval Station Roosevelt Roads in Puerto Rico[21] prompted the Coast Guard to discontinue flying E-2Cs and to return its E-2Cs to the Navy. The U.S Customs Service also returned its E-2Cs to the Navy and concentrated on the use of former U.S. Navy P-3 Orion aircraft in the CN role.

E-2C Hawkeye squadrons played a critical role in air operations during Operation Desert Storm. In one instance, a Hawkeye crew provided critical air control direction to two F/A-18 Hornet aircrew, resulting in the shootdown of two Iraqi MiG-21s. During Operations Southern Watch and Desert Fox, Hawkeye crews continued to provide thousands of hours of air coverage, while providing air-to-air and air-to-ground command and control in a number of combat missions

The E-2 Hawkeye is a crucial component of all U.S. Navy carrier air wings, and each carrier is equipped with four Hawkeyes (five in some situations), allowing for continuous 24-hour-a-day operation of at least one Hawkeye, and allowing for one or two of them to be undergoing maintenance in the aircraft carrier's hangar deck at all times. Until 2005 the US Navy Hawkeye’s were organised into East and West coast wings, supporting the respective fleets. However, the East coast wing was disestablished and all aircraft are now organised into a single wing based at Point Mugu, California. Six E-2C Hawkeye aircraft were deployed by the US Naval Reserve for drug interdiction and homeland security operations until March 9, 2013, when the sole Reserve squadron, VAW-77 'Nightwolves', was decommissioned and its six aircraft sent to other E-2C squadrons.

During Operation Enduring Freedom and Operation Iraqi Freedom all ten Regular Navy Hawkeye squadrons flew overland sorties. They provided battle management for attack of enemy ground targets, close-air-support coordination, combat search and rescue control, airspace management, as well as datalink and communication relay for both land and naval forces. During the aftermath of Hurricane Katrina, three Hawkeye squadrons (two Regular Navy and one Navy Reserve) were deployed in support of civilian relief efforts including Air Traffic Control responsibilities spanning three states, and the control of U.S. Army, U.S. Navy, U.S. Air Force, U.S. Marine Corps, U.S. Coast Guard, and Army National Guard and Air National Guard helicopter rescue units.

Hawkeye 2000s first deployed in 2003 aboard USS Nimitz (CVN-68) with VAW-117, the "Wallbangers", and CVW-11. U.S. Navy E-2C Hawkeyes have been upgraded with eight-bladed propellers as part of the NP2000 program; the first squadron to cruise with the new propellers was VAW-124 "Bear Aces". The Hawkeye 2000 version can track more than 2,000 targets simultaneously (while at the same time, detecting 20,000 simultaneously) to a range greater than 400 mi (640 km) and simultaneously guide 40–100 air to air intercepts or air to surface engagements.

VAW-120, the E-2C fleet replacement squadron began receiving E-2D Advanced Hawkeyes for training use in July 2010. Initial operating capability for an E-2D fleet squadron ready for operational deployment has slipped to October 2014.

Variants
W2F-1
Original designation of the Hawkeye, changed to E-2A in 1962.

E-2A
Initial production version, was W2F-1 before 1962. 59 built.

TE-2A
Two E-2As converted as crew trainers.

YC-2A
Two E-2As, BUNOs 148147 and 148148, converted as prototypes of the C-2 Greyhound

E-2B
As E-2A but fitted with improved computing, enlarged outer fins. 52 converted from E-2A.

YE-2C
Two E-2As, BUNOs 148712 and 148713, converted as E-2C prototypes. Designated as YE-2C and NE-2C respectively. These airframes then finished out their useful life being used as TE-2C pilot trainers.

E-2C
As the E-2B but with all new electronics, surveillance radar and search radar, 63 built. In "plus-models" the E-2C also has upgraded turboprop engines.

E-2C Group 0
Initial production version of E-2C, fitted with AN/APS-120 or AN/APS-125 radar. Lengthened nose compared to earlier versions

E-2C Group I
New radar (AN/APS-139), plus ungraded mission computer and upgraded engines. 18 new build aircraft.

E-2C Group 2
AN/APS-145 radar, further improved electronics.

E-2C Hawkeye 2000
New mission computer, Cooperative Engagement Capability (CEC and additional satellite communications aerial. Originally designated Group 2+.

E-2D
Currently undergoing flight testing and Initial Operational Test and Evaluation. This version will feature an entirely new avionics suite, improved engines, a new "glass cockpit" and the potential for air-to-air refueling.

E-2T
E-2C variant for Republic of China (Taiwan), with parts taken from retired E-2Bs (USN BuNos 151709, 151710, 151724, 152479) in order to please objections from the People's Republic of China and to make it appear as a sale of four rebuilt E-2As or E-2Bs. However, these aircraft have the same level of electronics as the E-2C Group II Hawkeyes with their APS-145 radars.