China recently announced that their new stealth fighter jet, the J-20, was a 'fourth generation' fighter. However, in the West, we call it a 'fifth generation' fighter. When did these fighter jet generations come about and what are they?

Caveat: I’m not a professional historian, but a pilot with a huge interest/passion in history with some insight into the history of fighter jets.

So I should first point out that there’s no official definition of what a generation of fighter jet is. You will hear various terms from the different nations/air forces of the world and even different manufacturers disagree, like Eurofighter disagreeing with Lockheed Martin on fifth generation fighters.

I know Wikipedia isn’t a great source, but this page does compile a lot of the different definitions of fighter jet generations from various sources and examples.

What is, then, generally agreed upon is that there is a first generation of fighter jets… the first jet fighters, of course. And most modern Western sources agree that the Lockheed Martin F-22 Raptor and F-35 Lightning II are in the ‘fifth’ generation of fighter jets.

So what sets them apart?

Fair warning: there is a TON more that goes on behind the scenes, such as differentiating between types of air intercept radars (even differentiating between pulse and pulse-doppler radars), than can be covered here. Also, a lot of the capabilities of modern fighter jets – and especially fifth generation fighter jets – are classified at levels well beyond anything that can be discussed which makes it hard to differentiate finer details between upgraded variants of fighters designed in the 70s and 80s and an F-22 or F-35.

I’ll be using a copy of Jane’s All The World’s Aircraft from 2013 for some specs/details as well as official sites, including military sites, to give public info on aircraft to help define the generations.

First Generation

The first generation of fighter jets is most easily understood as the first jet fighters to take to the sky. Aircraft like the Me262, P-80 Shooting Star, and F-86 Sabre are all considered to be a part of this generation. Using the first turbojet engines, capable of subsonic-only flight, they were largely built on the principles of WW2-era fighter planes carrying guns/cannons only. With rudimentary cockpits and simple gunsights, they were largely used on the same principles as WW2 propeller fighters except with the power of jet engines pushing them to higher speeds, altitudes, climb rates, turn rates, etc. than anything before.

Second Generation

This definition gets a bit murkier, but is typically used to cover that era of aircraft starting around 1950 through the early 60s when we see fighter performance being pushed to new heights, pun slightly intended. We see afterburning turbojet engines pushing aircraft well past the sound barrier.

Part of this was due to the prevailing philosophy of air combat in this day: with nuclear weapons only capable of being delivered by long range bombers like the B-36, B-47, and B-52, US fighter doctrine focused on what they imagined the Soviets would do: fly long-range bombers to the US and destroy our cities and bases.

Thus, the Air Force built interceptors to shoot down these bombers. And interceptors would need to be fast - hence the Century Series of fighters that all exceeded Mach 1 and even Mach 2 in top speeds. Fighters would be vectored to bomber formations either with Ground Control Intercept (GCI) stations using ground based radars... or aircraft like the F-102 Delta Dagger which had an on-board radars to help find the enemy and guide basic weapons.

The speeds at which these planes flew, and necessity for more lethal weapons to bring down bombers as well as one another, pushed the development of air-to-air missiles such as the heat seeking AIM-9 Sidewinder and radar guided AIM-4 Falcon. The F-102 even had the AIM-26 falcon… equipped with a nuclear warhead for when you absolutely positively want to destroy a bomber and its entire formation.

So you see that fighters of this era start moving away from the WW2 style of air combat involving WVR (within visual range) guns using basic gunsights to aircraft that can get to the fight at supersonic speeds, have radars to help find the enemy and guide weapons to them, and start using air-to-air missiles in their inventories – although these were largely only WVR capable and in limited weapons envelopes.

There’s also a ton of underlying stuff going on in this time: to counteract the high aerodynamic forces of high altitude and fast flight, aircraft use hydro-mechanical flight control systems en masse. The new levels of performance also necessitated the development of stability augmentation systems simply to keep planes from falling out of the sky.

One other key point: this generation focused heavily on single-purpose aircraft design. The limitations of avionics of the day meant that there simply wasn’t the room necessary on board for all sorts of computers to calculate, for instance, a missile intercept AND precision dropping of unguided bombs, so it became important to pick one or the other.

Third Generation

The third generation is a bit harder to define, but is typically seen as that era right before the Vietnam War through the tail end of the war. In contrast to the second generation of fighters which saw massive speed and performance improvements over the first generation, you see the third generation mature far more in avionics with a lot of the aerodynamic performance stuff having been figured out.

More advanced and powerful radars start being put in these planes – powerful enough that the McDonnell Douglas F-4 Phantom II necessitated a second crewmember, the Radar Intercept Officer, to utilize it.

We begin to see BVR (beyond visual range) missiles like the AIM-7 Sparrow become the weapon of choice. Analog avionics come into their own.

We see that dedicated ground attack aircraft of this generation get massive improvements in avionics as well: the LTV Corsair II is the first US aircraft with a HUD (Heads-Up Display) and features capabilities like a moving-map, tied into the inertial navigation system, so the pilot knows where over ground they are. The Grumman A-6 Intruder utilized a second crewmember, the Bombardier/Navigator, to manage the advanced DIANE (Digital Integrated Attack/Navigation Equipment) that used a combination of systems, like radars, to allow the plane to fly low levels in bad weather over and around terrain when the pilot couldn’t visually see outside. This radar information could be used to calculate a bombing solution as well, allowing bombing to occur accurately at night or in bad weather.

We also see that fighters, like the F-4, come to realize that all that thrust also makes them great at carrying large payloads. And so the F-4 starts dropping bombs – a lot of them in fact, as the F-4 has a maximum payload of over 18,000 pounds, nearly the same as a fully laden B-29 Superfortress in WW2.

With the advances in avionics (both in design and in electronics miniaturization), coupled with planes reaching the pinnacles of aerodynamic design and thrust, we start seeing jet fighters begin to excel at multiple roles that were once reserved for single-purpose aircraft. The first targeting pods and precision guided weapons – like the Paveway I laser-guided bombs and AGM-65 Mavericks enter service in this time, even being used in Vietnam before the war ended.

A testament to how capable and upgradable these aircraft were, the last US F-4’s were flown in December 2016 having been used in a variety of roles from target drone to testbed platform since the last operational uses of them, as Wild Weasels, in the 1990s.