Developed at the peak of the Cold War, the McDonnell Douglas F-15 Eagle was designed to compete against a Soviet fighter American military officials believed was all but unbeatable. America’s Defense apparatus looked at the record-breaking speed and power of the emerging MiG-25 and let their imaginations run wild, but the aircraft they designed to defeat this nightmare of their own creation was somehow even wilder.

When the F-15 as we now know it emerged from development, it came with an unprecedented combination of power, maneuverability, and advanced avionics that left it without equal anywhere in the world. Its powerful pair of Pratt & Whitney F100 afterburning turbofan engines could propel the Eagle from the ground to 30,000 feet in less than 60 seconds, and up to 65,000 feet — high enough to boil the blood of its pilot — in just over two minutes. In fact, a modified F-15, dubbed the Streak Eagle, broke eight climbing world records before the F-15 even entered service, reaching nearly 100,000 feet — 15,000 feet above the SR-71’s stated service ceiling — in about three and a half minutes. 

But the Eagle is much more than a rocket ship with wings. 

Through a combination of its immense power output and low wing loading (or the ratio of aircraft weight to total wing area), the Eagle is so nimble that Boeing test pilots have gone on record to say that the latest F-15EX, equipped with new fly-by-wire controls, can perform aerobatic maneuvers that are usually reserved for jets with thrust vectoring engines, or engine nozzles that can move independent of the airframe, found in super-maneuverable fighters like the F-22 or Russia’s Su-35.

Thanks to a constantly improving avionics suite and the addition of increasingly capable air-to-air missiles, F-15s may have been designed for close-quarters battles, but have evolved in BVR champs. In 2021, the US Air Force announced an F-15C scored the longest-ever reported air-to-air kill against a BQM-167 target drone — at a distance that has yet to be disclosed, but is understood to be in the triple digits. 

With an unmatched air combat record of 104 wins and zero losses, Eagles have been known to make it home after taking missile damage to engines, and even after losing an entire wing in an air-to-air collision. 

Within just three years of entering service, the Eagle proved so capable that McDonnell Douglas began work on an interdiction fighter/bomber based on the same airframe, ultimately resulting in the two-seat F-15E Strike Eagle  — a platform that has not only earned its own acclaim as an air-to-ground fighter in combat, but holds the distinction of being the only aircraft in history to score an air-to-air kill with a laser-guided bomb. 

But while the American F-15 lineage would grow to include the F-15E Strike Eagle in 1988 and the F-15EX Eagle II more recently, this broadly capable platform has been the basis for countless other cutting-edge efforts, some of which seem practically unreal. Here are just a few of them. 

F-15N: THE SEA EAGLE

In the early 1970s, Grumman’s F-14 Tomcat, intended for duty aboard America’s aircraft carriers, was facing looming concerns about its size, weight, and complexity, prompting McDonnell Douglas to propose modifying their F-15 concept (in development for the Air Force at the time) for duty aboard the Navy’s flattops. 

At a gross weight of 44,500 pounds, the F-15 was 16,500 pounds lighter than the Tomcat with a similar load. That’s the equivalent of an M198 howitzer with a fireteam of troops to run it. Because the F-15 had a relatively low weight-to-wing-area ratio, it was more maneuverable than the F-14, and its less problematic pair of Pratt & Whitney F100-PW-220 engines gave it a higher top speed, beating the Tomcat’s Mach 2.3 by a healthy 150 or so miles per hour.

But better than faster or more maneuverable in the minds of some lawmakers was its price. McDonnell Douglas was prepared to deliver F-15As to the Air Force at a sticker price of $28 million per aircraft (or about $227.5 million in 2024 dollars). High as that may seem, the larger and more complicated Tomcat rang in at $38 million per aircraft, or about $308 million today. That’s right… one F-14 at the time cost about the same as three F-35s today.

The F-15N concept swapped out the F-15A’s existing emergency tailhook with a larger reinforced one suitable for carrier operations and added heavier-duty landing gear and folding wings for easier stowage below deck. All told, the necessary modifications added only about 3,000 pounds to the aircraft, keeping the Eagle’s performance largely intact. But for all the speed, power, and cost savings the Sea Eagle could have offered… it fell well short of the F-14 in two areas that were vital for carrier defense: its radar and inability to carry as many hefty AIM-54 Phoenix missiles. 

The F-14’s massive AN/AWG-9 radar was the largest and most powerful ever affixed to a fighter until the emergence of the F-22 Raptor, and the system was purpose-built to be paired with the long-ranged Phoenix missile to take down Soviet bombers long before they could deploy anti-ship cruise missiles toward American carriers. The F-14, which was the largest American fighter ever to see carrier duty, could carry a half dozen of these massive missiles… whereas the F-15 could only carry one. With additional modifications to carry more AIM-54s, the newly dubbed ​​F-15N-PHX weighed in at 10,000 pounds heavier than a standard Eagle, eliminating its performance advantage. 

Ultimately, the Tomcat won out — but it’s still fun to think about how Top Gun would have been different with Maverick at the stick of a Sea Eagle. 

F-15 ACTIVE: THE THRUST-VECTORING EAGLE WITH CANARDS

In 1984, the Flight Dynamics Laboratory out of the Air Force Aeronautical Systems Division awarded a contract to McDonnell Douglas to begin development on an F-15 concept that would allow Eagles to take off and land on short or damaged runways, based on the assumption that airstrips would be early targets in a conflict with the Soviet Union. Among the changes incorporated to this end were 2-directional thrust vector control similar to that later found in the F-22 Raptor, and the addition of canards made out of the horizontal tail surfaces of an F/A-18 Hornet. 

The resulting F-15 STOL/MTD (Short Takeoff and Landing/Maneuver Technology Demonstrator) could take off at speeds as low as 42 miles per hour, and reduced the length of runway required for takeoff by 25 percent. To shorten landing requirements, the program leveraged reversible thrust from the aircraft’s engines in conjunction with its canards and TVC to reduce landing roll by a whopping 78%. While a standard F-15 Eagle needed more than 7,500 feet of clear runway to land, the F-15 STOL/MTD could do it in just 1,650.

In 1993, the Air Force handed the keys to their F-15 STOL/MTD to NASA for its new ACTIVE program, which was short for Advanced Control Technology for Integrated Vehicles. Building off of their previous digital flight control programs like HIDEC and Performance Seeking Control (PSC), NASA opted to retain the unusual wing layout of their new F-15 in the ACTIVE program, but added new Pratt & Whitney pitch-yaw balance beam nozzles (PYBBN) on a new set of engines; the F100-PW-229. Unlike its previous thrust vector control apparatus, these new nozzles offered a full 360-degree arc in which the nozzles could redirect outflow. As a result, NASA’s F-15 ACTIVE was the most acrobatically maneuverable Eagle ever to fly. 

These programs were never meant to lead to a production design, and were instead all about gathering valuable information about different flight regimes and the effect TVC and canards could have on an aircraft’s performance. The F-15 used for these programs was ultimately retired in 2009. 

F-15 GLOBAL STRIKE EAGLE: AN EAGLE WITH A ROCKET ON ITS BACK

In 2006, a team from Boeing proposed an incredible new use for America’s legendary F-15 Eagle that called for mounting a 45-foot rocket to its back. This rocket-carrying fighter would be given the seemingly logical (while still entirely dramatic) moniker of F-15 Global Strike Eagle, and it could have revolutionized how America deployed hypersonic weapons or put small payloads into orbit.

The idea was to use the Eagle’s powerful afterburning turbofan engines and the incredible amount of lift offered by its design to ferry rockets up to high speeds and altitudes before releasing them to ignite and fly the remainder of the journey into orbit. Launching orbital payloads from an aircraft would eliminate the need for expensive rocket launch facilities while making it possible for F-15s to rapidly deploy small payloads into orbit from anywhere on the planet with an airstrip and a hangar.

It was a relatively low-cost solution to a very expensive problem America’s military, particularly the Space Force, continues to tangle with today. But despite a very realistic approach to the Global Strike Eagle design, Boeing’s pitch likely still seemed a bit too crazy to put into practice… at least as far as we know.