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Are modern fighter jets bulletproof and armored? One would not be wrong given part of their operations is being on the receiving end of enemy ammunition shooting at them.

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With very select exceptions like the Su-34, and the A-10 if you consider it modern, they are not. Even in these cases only the pilot and a few critical parts are armored. Most of the aircraft's skin offers no meaningful resistance even to small arms.

Extensive armor coverage that could withstand modern air-to-air or surface-to-air weapons simply isn't viable for a fighter for weight reasons. Redundancy is used to resist near misses and light hits instead.

The reasons are different depending on the weapon. MANPADS like the Stinger go for the nearest heat source (engine exhaust). Their capabilities against a fighter are limited to fringe cases (flying too low, caught on landing/takeoff, and a very lucky shot), and armoring the engine nozzle isn't viable anyway.

The lightest effective anti-aircraft weapon, the Sidewinder, uses a continuous rod warhead, a ring of steel expanding at almost 1 km/s. Due to high inertia, it will cut through anything except for the engine, major bulkheads and longerons, and hard elements like the A-10's "titanium bathtub". Aramid lining, which is the only thing a modern fighter could afford weight-wise for full-airframe protection, will be cut.

The heaviest is the S-400 SAM, which intercepts the target at 2 km/s with a 180 kg fragmentation warhead. The resulting hypervelocity impact (3+ km/s) has solids behave like liquids, with impact results determined by mass rather than strength. The low odds of surviving a warhead this size aside, when it's mass that determines these odds, it's always better invested in something functional rather than just armor.

Most mid-size AAM and SAM also fly an intercept course at high velocity and use high-brisance explosives for blast fragmentation. Against resulting high impact velocities, mass is better invested in more redundant hardware, not armor. That is very different from low velocities, common on the ground, where thin layers of high-strength materials can prevent projectile penetration.

Larger fighters are indeed more resistant to damage than smaller lighter ones (see the one-wing F-15). Armoring a few critical elements can help improve survivability, but this armor has to be very localized. The Su-27 family has an armor plate between the engines, so that one wouldn't damage the other if it disintegrates after a hit. Close air support (CAS) aircraft that attack tanks and other ground vehicles carry some protection for the pilot - notoriously vulnerable to punctures, unlike most of the plane - against ground fire.

A combination of these factors is why armor has largely become limited to CAS aircraft: high-strength armor is very weight-effective against the low velocities of land warfare weapons, but much less so against hypervelocity impactors and fragments used in air combat.

See a related question for a few more bits of info on aircraft armor and protection: Why do modern fighter jets use 20mm guns?

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  • $\begingroup$ Might be worth noting what CAS stands for $\endgroup$ – Notts90 Feb 2 at 22:16
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Some are. Most notably the A-10 Warthog carries about 1200 LBS of titanium armor up front to protect the cockpit.

A lot of modern fighters have self sealing fuel tanks which is a type of bulletproofing in a sense. It allows the airframes fuel tanks to be hit, but unaffected by bullet fire.

Broadly speaking additional armor adds weight which is generally viewed as a bad thing in aviation.

Aircraft designs also focus on things like redundancy so that they can be hit by multiple rounds of ammunition and have backup systems in place if and when a bullet strike takes out an important system.

There is some more discussion here.

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    $\begingroup$ Note that the A-10 Warthog is armored this way precisely because it is not a fighter, it is a ground attack aircraft. It is specifically designed to be shot at, i.e. to fly low and slow above and across an active battlefield. It's closer to a tank than to a fighter in that respect. It is an airframe quite literally built around a huge gun, with a high focus on survivability: the high mounted engines, twin control surfaces, multiply redundant control systems, and the titanium tub the pilot and critical control systems sit in. $\endgroup$ – Jörg W Mittag Feb 2 at 2:19
  • $\begingroup$ My favorite sentence from the Wikipedia article: "The aircraft is designed to be able to fly with one engine, one half of the tail, one elevator, and half of a wing missing". $\endgroup$ – Jörg W Mittag Feb 2 at 3:27
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Generally speaking, armor is contradictory to flying. Besides, modern fighters fly so high above any small arms fire, at the very least at 10,000 ft, that bullets simply isn't even a very remote concern to fighters. Fighters are much tougher than they were back in WWII, but that's because they must sustain the high G load at high-speed cornering rather than the need to survive gunfire.

However, if we are talking about cannon fire, then it is a very real concern to modern fighters. The US uses 20mm, the Europeans 27mm and the Russians prefer 30mm. Each shot from any of these rapid firing cannons can outright blow a hole in any aircraft, and there is no way any amount of armor against these big guns can be added to fighters without making them too heavy to fly. Fortunately, the unpowered projectiles from these guns can only fly for less than 2 miles before their trajectories start to droop significantly, so generally, fighters rarely get a chance to use these armaments in real combats.

The real threat to modern fighters is air-to-air missiles that they themselves are armed with and surface-to-air missiles. As long as fighters keep away from these threats absolutely nothing can shoot them down. As long as these two kinds of missiles are not a real concern after the enemy air force and SAM batteries are dealt with, fighters can fly with near impunity.

The A-10 is a CAS aircraft, and it is used against cheap targets that aren't worth smart bombs or air-to-surface missiles. CAS is not in vogue anymore, and the USAF keep them because they cost so little, not because they have to fly almost face to face against the enemies. Besides, the armor A-10 is carrying isn't real armor. Real armor stops or bounces back projectiles, the A-10's armor absorbs the projectile without letting it through.

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    $\begingroup$ I'm surprised as to why you'd consider the A-10's armor to be "not real". First of all, being titanium, it will stop/bounce back projectiles just as well. Second, main battle tank armor is definitely real, and most of it is designed to "absorb" the projectile. Both KEP (APFSDS) and HEAT, which are the only viable threats to modern tanks in the frontal arc, cannot be stopped or bounced except at very oblique (85+ degree) angles due to their hypervelocity nature introducing liquid-like behavior in materials, but are rather "absorbed" by the armor. $\endgroup$ – Therac Feb 2 at 9:42
  • $\begingroup$ @Therac Don't most modern battle tanks use reactive armor? $\endgroup$ – TomMcW Feb 3 at 22:31
  • $\begingroup$ @TomMcW Reactive armor is a layer placed on top of normal composite armor, used to break up HEAT jets and sometimes KEP. It's only an addition (or rather an effectiveness multiplier) for passive armor. $\endgroup$ – Therac Feb 4 at 10:40

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