[5] In April 1965, Harold Brown, at that time director of the Department of Defense Research and Engineering, stated the favored position was to consider the F-5 and begin studies of an "F-X".

Typical designs featured variable-sweep wings, weight over 60,000 pounds (27,000 kg), included a top speed of Mach 2.7 and a thrust-to-weight ratio of 0.75.

Although improved training and the introduction of the M61 Vulcan cannon on the F-4 did much to address the disparity, these early outcomes led to considerable re-evaluation of the 1963 Project Forecast doctrine.

[12][13] This led to John Boyd's energy–maneuverability theory, which stressed that extra power and maneuverability were key aspects of a successful fighter design and these were more important than outright speed.

The resulting studies took 18 months and concluded that the desired features were too different; the Navy stressed loiter time and mission flexibility, while the Air Force was now looking primarily for maneuverability.

[20] Both Headquarters USAF and TAC continued to call for a multipurpose aircraft, while both Disosway and Air Chief of Staff Bruce K. Holloway pressed for a pure air-superiority design that would be able to meet the expected performance of the MiG-25.

[22] Four companies submitted proposals, with the Air Force eliminating General Dynamics and awarding contracts to Fairchild Republic, North American Rockwell, and McDonnell Douglas for the definition phase in December 1968.

The Air Force announced the selection of McDonnell Douglas on 23 December 1969; like the Navy's VFX, the F-X skipped much of the prototype phase and jumped straight into full-scale development to save time and avoid potential program cancellation.

Other improvements included strengthened landing gear, a new digital central computer,[31] and an overload warning system (OWS), which allows the pilot to fly up to 9 g at all weights.

The F-15E strike variant was selected for production over General Dynamics' competing F-16XL in 1984; it is a two-seat, dual-role, totally integrated fighter for all-weather, air-to-air, and deep interdiction missions.

[37] For low-altitude, high-speed penetration and precision attack on tactical targets at night or in adverse weather, the F-15E carries a high-resolution APG-70 radar and LANTIRN pods to provide thermography.

[39] Beginning in 2006, with the threat of curtailed procurement of the F-22 that was to replace all air superiority F-15s, USAF planned to modernize 179 F-15Cs in the best material condition in order to maintain fighter fleet size by retrofitting the AN/APG-63(V)3 AESA radar and updated cockpit displays; the first upgraded aircraft was delivered in October 2010.

[46][47][48][49] The 2040C upgrade for the F-15C/D was not pursued, owing to the airframes' age that made it not economically sustainable, but many of the components such as EPAWSS and AESA radar were continued for F-15E upgrades as well as new-build F-15EX Eagle II ordered by USAF in 2020; the F-15EX took advantage of existing Advanced Eagle production line for export customers to minimize lead times and start-up costs to replace the remaining F-15C/Ds, whereas F-22 production restart was considered cost-prohibitive.

[51][52][N 2] The empennage is of metal and composite construction, with twin aluminum alloy/composite material honeycomb structure vertical stabilizers with boron-composite skin, resulting in an exceptionally thin tailplane and rudders.

The cockpit is mounted high in the forward fuselage with a one-piece windscreen and large canopy for increased visibility and a 360° field of view for the pilot.

At certain speeds, the dynamic thrust output of the dual engines is greater than the aircraft's combat weight and drag, so it has the ability to accelerate vertically.

Visibly, the F-15 has a unique feature vis-à-vis other modern fighter aircraft; it does not have the distinctive "turkey feather" aerodynamic exhaust petals covering its engine nozzles.

Following problems during development of its exhaust petal design, including dislodgment during flight, the decision was made to remove them, resulting in a 3% aerodynamic drag increase.

Subsequent wind-tunnel tests on a one-wing model confirmed that controllable flight was only possible within a very limited speed range of ±20 knots and angle of attack variation of ±20 degrees.

This display, visible in any light condition, provides the pilot information necessary to track and destroy an enemy aircraft without having to look down at cockpit instruments.

The APG-63(V)2 and (V)3 are compatible with current F-15C weapon loads and enable pilots to take full advantage of AIM-120 AMRAAM capabilities, simultaneously guiding multiple missiles to several targets widely spaced in azimuth, elevation, or range.

The F-15 in early service was plagued by reliability and durability problems of its F100-PW-100 engines, whose ambitious specifications were critical for the aircraft's high performance.

[67] Israeli air-superiority F-15 variants have since been extensively upgraded to carry a wider range of air-to-ground armaments, including JDAM GPS-guided bombs and Popeye missile.

F-15s of the 33rd Tactical Fighter Wing provided air cover alongside U.S. Navy F-14 Tomcats for Marines and the 82nd Airborne Division for contingency operations in Grenada.

[77] The F-15C and D fighters were used in the air-superiority role, while F-15E Strike Eagles were used in air-to-ground attacks mainly at night, hunting modified Scud missile launchers and artillery sites using the LANTIRN system.

[91] The accident review board report, which was released on 10 January 2008, stated that analysis of the F-15C wreckage determined that the longeron did not meet drawing specifications, which led to fatigue cracks and finally a catastrophic failure of the remaining support structures and breakup of the aircraft in flight.

To keep the F-15C/D viable, the fleet saw a series of upgrades, with 179 aircraft receiving the AN/APG-63(V)3 AESA radar starting in 2010 along with eventual addition of IRST pods and cockpit enhancements.

[102] In late 2018 and early 2019, following a series of DoD Cost Analysis and Program Evaluation (CAPE) Office studies on affordably recapitalizing the fighter fleet, the Pentagon in its FY 2020 budget requested new-build F-15EXs — an advanced variant based on the export F-15QA then in production — to replace the F-15Cs and supplement the F-22s to maintain fighter fleet size, with planned total procurement of 144 aircraft.

Houthi sources claim to have downed the F-15, although this has been disputed, as the missile apparently proximity detonated, though the F-15 continued to fly in its trajectory seemingly unaffected.

[110][111] Saudi official sources confirmed the incident, reporting that it happened at 3:48 pm local time after a surface-to-air defense missile was launched at the fighter jet from inside Saada airport.