The Air Force's F-15 Eagle, F-16 Fighting Falcon and A-10 Warthog, along with the Navy’s F/A-18 Hornet, are all 1980s-era aircraft that have been updated numerous times over the years. As a result, new software, weapons, avionics and targeting technologies have made these fourth-generation airplanes relevant and useful today.

But are there limits to how much an older airframe and aerodynamic design can be upgraded?

New weapons, avionics, computing, software and targeting systems can’t make a fourth-generation plane stealthy, so if the Defense Department’s plans for large numbers of F-35 jets are canceled or massively reduced, then the United States might find itself with an overwhelming majority of fourth-generation fighter jets as it moves toward the future. This circumstance, should it come to fruition in any capacity, could put the United States at serious risk of being massively outmatched countries with fifth-generation capable forces, such as Russia or China. 

Ultimately the aerodynamic design of a fourth-generation fighter can’t be stealthy as there are simply too many angled protruding edges and contours detectable by electromagnetic radar return signals. There are hundreds of F-15 jets, F-18 jets and F-16 jets, as they make up the majority of the Air Force and Navy’s air fighter jet force. 

Interestingly, while Navy F-18 developers did not believe they could engineer a stealthy fourth-generation plane, they did make several efforts to lower the radar cross-section of the aircraft and add some small measure of stealth properties to the jet.

For example, years ago the Navy engineered F-18 jets with conformal fuel tanks woven into or blended into the fuselage of the aircraft. This was intended to extend combat radius and mission dwell time by adding extra fuel, while also smoothing or “rounding” the structure of the fuselage to lower its radar signature. Around the same time period, the Navy built somewhat rounded external weapons carrying pylons to create a smoother exterior and, much like an internal weapons bay, prevent the jagged edges of externally mounted weapons to generate a radar return signature. The more different angles a series of radar pings have to bounce off of, the more detailed it return signal rendering. Blended horizontal shapes, however, such as the wing-body blended fuselage of stealthy airplanes like the F-35 jet and F-22 jet, generate a much different and much less detectable radar return signal.

What much of this amounts to is that, no matter how many upgrades improve avionics, electronics, targeting precision, and weapon guidance, a 1980s fighter jet simply cannot be stealthy. This places the aircraft at a tremendous disadvantage against enemy fifth-generation fighters and advanced air defenses. It may mean that fourth-generation planes simply are not in a position to deter Russian or Chinese fifth-generation fighters and not in a position to operate against air defenses such as Russian-built S-400 and S-500 missile defense systems. While few people would be quick to call fourth-generation fighter jets useless, as they can deliver great value in conflicts wherein the United States already has air superiority, these military airplanes may provide limited added value in a potential great-power confrontation. 

Truncating or canceling the Pentagon’s plan to arm its forces with large numbers of F-35 jets might massively increase the risk to the United States and render its air forces extremely vulnerable against major-power rivals armed with fifth-generation airplanes.

Kris Osborn is the defense editor for the National Interest. Osborn previously served at the Pentagon as a Highly Qualified Expert with the Office of the Assistant Secretary of the Army—Acquisition, Logistics & Technology. Osborn has also worked as an anchor and on-air military specialist at national TV networks. He has appeared as a guest military expert on Fox News, MSNBC, The Military Channel, and The History Channel. He also has a Master’s Degree in Comparative Literature from Columbia University.