The Fairchild Republic A-10 Thunderbolt II – also known as Warthog – is an impressive aircraft. Well-liked by crews and servicemen, it is legendary in every sense of the word.
It also has a fandom that few other jets can rival. Popular with both aviation geeks and military enthusiasts worldwide, the A-10 even has its own rallying cry: the “BRRRT” – the approximation of the sound its gun makes.
The power of that gun certainly has a lot to do with A-10’s fame. Called the GAU-8, it is a seven-barreled hydraulically powered rotary cannon that can fire up to 70 soda can-sized projectiles every second. In addition, the aircraft can carry an enormous amount of ordinance, is impressively maneuverable, and was built to survive incredibly heavy damage. There are numerous photographs of it returning to base with hundreds of bullet holes across the fuselage.
The jet’s merits are well-publicized and well-known, with the unmistakable silhouette of the A-10 above the desert among the most iconic images of modern aerial combat.
However, with fame comes misconceptions. Some of them originate from misunderstandings surrounding the plane’s technical aspects, others date back to the time when A-10’s characteristics were secret. Nevertheless, some carry a grain of truth.
So, here at AeroTime we decided to compile a list of the myths, and find out what is true and what isn’t. Each explanation is based on official and publicly available sources, with the main ones being two extensive books on the aircraft: ‘A-10 Thunderbolt II (Warthog) Systems Engineering Case Study’ by David R. Jacques and Dennis D Strouble, and ‘Fairchild Republic A-10 Thunderbolt II’ by Peter C. Smith. In addition, links to other books, technical manuals, interviews with pilots and other sources are provided in the article.
10. The A-10 is heavily armored
While the iconic aircraft has some armor, it’s not a flying tank. The durability of the A-10 doesn’t come from the armor, but from the clever layout, double-redundant systems, good controllability and other design features.
The A-10’s fuselage is covered only by thin aluminum skin, and the famed ‘titanium bathtub’ – a box that houses the pilot and avionics – is designed to protect only from small arms fire. Despite various claims, bullets that are bigger than rifle caliber can penetrate the armor at certain angles and distances.
The ‘titanium bathtub’ is a box, bolted together from metal sheets between 0.5 In (12.5 mm) and 1.5 In (38 mm) in thickness. It was designed to reliably protect the pilot and aircraft controls from small arms fire and fragments coming from below. Contrary to popular belief, A-10’s canopy (the glass top of its cockpit) is not armored.
The effectiveness of the bathtub is often overstated too, with less-than-reliable sources claiming that it can shrug off shells from 23 mm, 37 mm or even 57 mm anti-aircraft guns. What really should be made clear is that the armor can stop fragments coming from shells exploding nearby.
Direct hits of anything bigger than 23 mm – especially if an armor-piercing ammunition is used – can penetrate even the thickest points of the bathtub. There is ample data to show that armor-piercing rounds of 23 mm cannons, or even 14.5 mm and .50 caliber heavy machine guns, can pierce around or slightly over 20 mm of rolled homogenous steel armor (which is, generally, similar or very slightly softer than titanium) at combat distances and shallow angles. Thus, they can go through thinner plates of the A-10’s armored bathtub, while being stopped by thicker ones.
So, while the A-10 is quite heavily armored for an aircraft, the qualities of its armor are sometimes exaggerated by its fans. The Warthog is not an invulnerable armored beast some claim it to be.
9. The A-10 is either invulnerable or very vulnerable to MANPADS
Proponents of the A-10 claim that man-portable air-defense systems (MANPADS) are no threat to the aircraft due to its maneuverability, countermeasures and armor, while opponents say that the A-10 would not last a minute if targeted by anti-aircraft missiles.
The truth is somewhere in the middle: we have quite a bit of data on the performance of the A-10 in actual combat, and that data shows both extreme points as grossly exaggerated.
There are numerous cases of the A-10 being shot down by both MANPADS and other kinds of missiles in Iraq. And there have been cases of the aricraft being heavily damaged and returning to base. In some cases, the aircraft’s countermeasures worked well, and in some cases they did not.
Cases of the A-10 being damaged and limping home on one engine show that MANPADS pose a serious threat to the aircraft, which is why A-10s have only been deployed in low-risk areas since the late 1990s. However, the airplane is likely to survive a hit from a missile, even if that hit is going to incapacitate it.
The A-10 was designed in the late 1960s when man-portable anti-aircraft missiles were still in their infancy and cannons were a big threat. However, the aircraft was future-proofed to a certain degree: its heat signature was minimized by cleverly placing high-bypass turbofan engines over the tail. Furthermore, the jet was fitted with countermeasure systems that dispensed flares and chaff: the former intended to lure away infrared-guided systems, the latter – radar-guided ones.
In 2005, as the whole USAF A-10 force was modernized to the C variant, the countermeasure systems were heavily upgraded. However, it must be noted that flares do not have a 100% chance of negating a MANPADS attack, as demonstrated by the well-documented combat performance of the A-10.
Six A-10s were lost in combat, three of them shot down by MANPADS and three more by vehicle-mounted infrared-guided missiles during the operation Desert Storm in 1991, according to the official report of USAF combat losses. An official evaluation of the campaign by the US military shows that three more A-10s were damaged by heat-seeking missiles but managed to return to base, while 11 more were heavily damaged by other kinds of anti-aircraft fire. However, probably the best-known example of the A-10 surviving a MANPADS hit comes from the Iraq war of 2005, when the A-10 piloted by Captain Kim Campbell was heavily damaged over Baghdad, but still returned to base.
What do we make of that? There is no doubt that the A-10 is a sturdy plane, and can – and in many cases will – survive a missile hit. However, the MANPADS which damaged and shot down A-10s over Iraq were SA-16s that date back to the early 1970s, and even against them the A-10’s countermeasures did not always work. Furthermore, the airplanes that survived attack were heavily damaged. They had to abort the mission and were as good as lost for the rest of the campaign.
So, A-10s shrugging off any kind of anti-aircraft fire is a myth. A-10s being unable to survive in any kind of contested environment is a myth too.
8. A-10 was the first armored aircraft
Continuing the theme of the A-10’s armor, in various documentaries and descriptions of the jet’s armored bathtub, it is portrayed as an outstanding innovation and a feat of ingenuity.
The truth is that the A-10 wasn’t the first aircraft to use this kind of feature. The history of armored aircraft stretches back to WWI, and the Warthog is just another iteration of the concept which was successfully implemented before.
For one, A-10 was conceived as a replacement for the A-1 Skyraider, which featured an impressive collection of armor plates around the nose. They were not joined into a single structure, yet protected both the pilot and certain parts of the engine.
However, the best-known armored aircraft – as well as the inspiration for the A-10‘s protective system, as its development documentation indicates – was the Ilyushin Il-2 Shturmovik, a WWII-era Soviet ground attack plane. Its armored bathtub, made of steel, covered an entire center-section of the plane and provided protection for the crew, engine, avionics and fuel tanks.
Was the Il-2 the first armored aircraft? Not even close. As far back as WWI, various countries had begun experimenting with armoring their aircraft, and although those biplanes and triplanes were not exactly powerful by today’s standards, the armored bathtub has roots in that era.
The German Junkers J.1, which entered service in 1917, is often credited as world’s first armored aircraft and features a steel bathtub similar to the one later seen on the A-10. Of course, it was only 5 millimeters thick and barely enough to stop a rifle round, but the trend had to start somewhere.
So, A-10 is in no way the first armored aircraft.
7. Pierre Sprey designed the A-10
Pierre Sprey was an engineer who was part of an arguably influential lobbying group, known as the ‘Fighter mafia’ or ‘the Reformers.’ According to memoirs of Sprey’s comrades, he designed every fighter jet the US built between the 1960s and the 1990s.
The truth is, he did not. Despite appearing in countless documentaries that credit him with working on the F-15, the F-16, the A-10 and other jets, Sprey never worked at Fairchild Republic, McDonnell Douglas or General Dynamics, the companies that created the jets he supposedly designed. The Fighter mafia contributed to the creation of the 4th generation of fighter jets, but the extent of that influence is also heavily debated.
The A-10 was actually designed by Alexander Kartveli, one of Fairchild Republic’s most prolific engineers. Fighter mafia’s and Sprey’s role in the design is highly debatable and can be described as ‘influence’ at best. And while Sprey was one of the staunchest and most vocal proponents of the A-10 in later years, he did not design the plane.
There are several reasons behind this bone of contention. For one, according to some claims, the Fighter mafia, together with Pierre Sprey, were instrumental in formulating requirements that led to the creation of the A-10. Supposedly they were the ones to come up with the idea of an anti-tank aircraft with a gun as its primary armament.
Many of the experts who wrote books on the issue – including David R. Jacques and Peter C. Smith – disagree with this. According to them, the birth of the A-10 was not as straightforward, with many influences from various groups – primarily within the US Army and the Air Force – shifting and overlapping in a clash between doctrines. Also, the GAU-8 was never considered as the primary armament of the A-10 – the gun was just one of many requirements that were put forward.
Additionally, many events the proponents of the Fighter mafia display as evidence of the group’s influence happened in the mid-1970s, when the A-10 was already designed and flying. This suggests that Sprey’s contribution to the project probably came too late to make any difference.
There is another claim: that of the influence of the Blitzfighter – a concept aircraft designed by Fighter mafia’s James G. Burton – on the A-10. The Blitzfighter bears an uncanny resemblance to the Warthog, with its tail-mounted engines, a 30 mm cannon in the nose, and an emphasis on survivability.
There is just one problem: contrary to many claims, the A-10 appeared earlier than the Blitzfighter, and not vice versa. As Burton himself admits in his book, ‘The Pentagon Wars: Reformers Challenge the Old Guard’, he only started working on the concept in 1978, and proposed his design as a replacement for the A-10 which he saw as too expensive, too complex and too reliant on technology.
Somehow, in the minds of the Fighter mafia’s supporters, the chronology of the events was flipped, and the Blitzfighter was presented as the forerunner to the A-10.
6. A-10 strafes targets in a line
It has been featured in many films and video games:
As the A-10 flies above the target, the area in front and below the aircraft lights up with hundreds of small explosions, one slightly in front of another, in a trail of destruction.
Can combat aircraft strafe targets in a line? Absolutely. A tactic of firing guns in a gentle dive, while slowly transitioning to a level flight, is something that aircraft have done since WWI. It allows the engagement of multiple targets at once, with devastating effects on columns or larger formations.
Is this how A-10s typically attack their targets? No. The vibration of the GAU-8 is very powerful and can throw the pilot’s aim off, so, a special system locks the aircraft’s controls as soon as the trigger is pressed. Hence, all the videos that portray A-10 performing an actual attack show the aircraft aiming at one particular spot, firing, and then switching onto another target.
But in films, A-10’s attacks always look different. From serious war dramas to cheesy blockbusters, many Hollywood movies that feature the A-10 include the cliché of A-10 strafing targets in a line.
The system that prevents the aircraft from doing so is called Precision Attitude Control (PAC): a rudimentary autopilot which takes over the control of the aircraft as soon as pilot pulls the trigger. It is just one of a variety of systems designed to protect the aircraft from the adverse effects of its giant gun.
Truth be told, PAC can be switched off by the pilot. That would allow the A-10 to strafe targets in a line, just like the ground attack aircraft from WWII. However, not only would that be counterproductive, it could also put the jet and its pilot in danger. And so, videos that show the A-10 firing its gun in combat or training feature an attack on one target, with the PAC system turned on.
So, this myth is decidedly false: A-10s typically do not strafe targets in a line.
5. A-10 has the most powerful gun of any aircraft
Another staple of sensationalist documentaries, this myth is not easy to unravel.
There are many ways to measure the power of a weapon. Some WWII fighters used cannons that had bigger caliber and muzzle velocity. Some other Gatling guns have a higher rate of fire.
However, if we take the combination of these factors, the only other aircraft gun that can compete with the GAU-8 is the GSH-30-8, a Soviet-designed aircraft cannon used on the MiG-27 strike aircraft.
The GSH-30-8 fired a projectile of approximately the same weight as the GAU-8, but its muzzle velocity was somewhat slower. However, the firing rate of the Soviet weapon was much higher: between 5,500 and 6,100 rounds per minute against GAU-8’s maximum of 4,200 and normal rate of 3,900.
This made the GSH-30-8 very powerful, but but it also brought problems: the MiG-27 did not have all of the recoil-mitigating features of the A-10. The gun could literally rip its airplane apart – a story which is as strange as it sounds.
As a result, the firing rate of the GSH-30-8 was reduced in the 1980s. With this in mind, could the Soviet gun rival the GAU-8? Let’s take a deep dive into the numbers.
The most obvious way to measure the power of a weapon is its caliber. By that measure, the GAU-8 is among the most powerful in the arsenal of the US Air Force: the diameter of the bore of its barrels is 30 mm (1.18 inches). However, 30 mm is very popular across the world, with nearly all modern European, Russian and Chinese fighter jets sporting single-barrel 30 mm cannons.
These guns pale in comparison with the cannons carried by WWII-era tank busters, though. For example, the German Junkers Ju-87G Stuka had two 37 mm guns under its wings; many countries experimented with 45- and 50-mm cannons, while the US and Germany even mounted 75 mm tank guns on some bombers.
In comparison with some of these weapons, the caliber of the GAU-8 is not that impressive. However, the caliber alone does not determine the power of the gun. The size, weight and speed of the projectile must be taken into account too, and the 30×173mm of the GAU-8 is indeed among the most powerful 30 mm rounds. But it is still less powerful than, for example, the 30×250 mm round fired by the RMK30 gun of Eurocopter Tiger.
Another factor we have to consider is the rate of fire: the GAU-8 is a seven-barrel Gatling gun and fires much faster than any single-barrel cannon ever could. With the rate of fire of 3,900 rounds per minute (although originally intended for 4,200 rounds per minute) the GAU-8 is somewhat slower-firing than many smaller-caliber Gatling guns, such as the M61 Vulcan (6,000 rounds per minute).
By combining the factors mentioned above, we can get a fairly accurate measure of a weapon’s power. Such a way of calculating firepower is very popular, and it shows that in standard configuration (3,900 rounds per minute with a mix of one high-explosive and four armor-piercing projectiles) the GAU-8 sends forward over 25.5 kilograms of shells per second.
While that is a lot, the GAU-8’s closest competitor – the GSH-30-6 – is more powerful: the Soviet gun shoots 25.9 kilograms per second in standard configuration (4,000 rounds per minute with a mix of two hih-explosive and one armor-piercing projectiles), and 39.7 kilograms with non-reduced firing rate.
We could also factor in the speed of the projectile. The muzzle velocity of the GAU-8 is 1,010 meters per second (3,324 feet per second) – much faster than GSH-30-6’s 845 meters per second (2,770 feet per second). This gives the 30×173mm round significantly bigger muzzle energy: roughly 194,000 joules for high-explosive and 203,000 joules for armor-piercing projectiles. GSH-30-6’s 129,000 joules are much less than that. However, with non-reduced firing rate, the Soviet gun still came on top when it came to energy per second.
There are other, even more complex ways to calculate the power of a weapon, such as the ones used by Anthony G Williams and Emmanuel Gustin in their articles and books. They factor in not only the energy of the projectile but the amount of explosive material contained in the cartridge, as well as the weight of the weapon itself. While such a calculation is well beyond the scope of this article, it’s safe to say that the GAU-8 and the GSH-30-6 are close contenders.
So, is the GAU-8 the most powerful aircraft gun in the world? Yes, it is now, especially since all the GSH-30-8-equipped MiGs were retired.
4. A-10 strafes tanks from above
This often-repeated myth states that the A-10 was created to exploit one of the disadvantages that all tanks have: the thinness of their top armor.
Mainly intended to fight ground-based enemies, tanks are extremely well armored in the front, with decent protection on the sides and rear: those are the directions the tank is the most likely to be shot at from. However, armoring the top is difficult, as that would increase the weight immensely, and serve little purpose.
And so the logic goes that even the best-armored tanks are very vulnerable if you attack them from the top. WWII-era dive-bombers did that. Supposedly the A-10 can as well.
Is it possible? Yes. However, the practice is incredibly dangerous, and it was not the primary way the A-10 was intended to be used.
A-10 pilots were trained to fly low and attack the sides and the rear of tanks, without resorting to trying to punch through the roof of a tank. Such an attack profile was imperative to avoid being shot down by anti-aircraft fire, and fairly effective against Soviet tanks of the time.
In addition, the speed of the A-10 makes attacking in a dive highly impractical – much faster than WWII-era bombers, the Warthog was simply not designed for that.
Strafing the target from its side, in nearly-level flight, was always the intended use of the GAU-8. Its ammunition was developed to penetrate the side armor of the T-62 tank, and the targeting system was designed with such a use in mind. In fact, a lot of testing was conducted to fine-tune such aspects as the angle at which the gun is mounted.
As the development documentation shows, attacks with dive angles of 50 to 70 degrees were considered too. But they were intended for dropping unguided bombs, not strafing.
The ideal angle for the gun run was considered to be less than six degrees. There are multiple reasons for that. First of all, even at the minimum speed of 200-300 knots (370-550 kilometers per hour) the window of opportunity for firing the weapon is too small. In addition, the Soviet-armored formations – the prime target for the GAU-8 – always had ample air defenses, and the slow dive in a straight line would make the aircraft too vulnerable.
As a result, A-10 pilots during the Cold War were trained to fire at the sides and the rear of tanks.
Sure, one can find ample footage of A-10s firing at steeper angles during the wars in the Middle East. However, these operations were conducted in a near-absence of anti-aircraft weapons.
3. GAU-8 is effective against modern tanks
This is a controversial one. Under no circumstances can the GAU-8 be considered as an effective weapon to fight modern main battle tanks (MBTs). The tanks’ side and rear armor is simply too thick, composed of numerous layers and additional explosive reactive armor (ERA) blocks.
The GAU-8 was created with the Soviet tanks from the 1960s – mainly T-55s and T-62s – in mind. Later tanks, be they Soviet, Russian, Chinese, European or American, are much more heavily armored, and cannot be penetrated by the GAU-8.
Let’s start with the hard numbers.
When designed in the 1960s, the GAU-8 and its 30×173mm PGU-14/B armor-piercing projectile with depleted uranium core was more than sufficient to penetrate the side and rear armor of the majority of Soviet tanks.
On paper it can punch through 55 millimeters of rolled steel when fired from 1,200 meters and up to 76 millimeters when fired from 300 meters at 30-degree angle. Better penetration could be achieved at steeper angles, and at shallower angles the penetration is much smaller.
The front, side and turret armor of most modern tanks is much thicker than that. Modern Soviet and Russian tanks, such as the T-64, the T-72, the T-80, the T-90 and their variants, have a minimum of 60 mm of steel armor on their sides and back. Western and Chinese tanks of the same generations have roughly similar level of protection.
However, nearly all modern tanks also sport composite armor – additional layers of protection such as steel-aluminum-steel sandwich of the T-72A or something more high-tech on Western vehicles. Furthermore, ERA covers the most vulnerable areas of modern tanks, and while older types of such armor are only effective against high-explosive anti-tank (HEAT) rounds, latter ones were designed specifically with kinetic penetrators in mind.
Despite all this protection, several vulnerable areas remain, such as lower side plates between the tank’s rollers (wheels) on the tanks without side skirts. Furthermore, with the GAU-8 spraying 70 shells per second, multiple hits on the same spot may appear possible.
While possible, that is extremely unlikely. Consider this test performed by the USAF in 1979. In conditions that simulated hostile airspace, an A-10 attacked a formation of ten M47 Patton tanks, firing 174 rounds in short bursts at an average range of 753 meters (2470 feet). Some 90 rounds hit the tanks, but only 30 of them penetrated the armor. Three tanks were destroyed, four more immobilized, and three of those sustained damage to their weapons systems.
The dispersion of rounds, the speed of the aircraft and a need to evade anti-aircraft fire make sustained fire on one target – which would increase the probability of hitting vulnerable areas – nearly impossible. In the best of circumstances, the A-10 can fire just a short burst at one target before having to disengage, which is precisely the reason its gun was designed with such an extreme rate of fire in mind.
Hence, modern main battle tanks are practically invulnerable to the GAU-8. However, as stated above, other kinds of armored vehicles are still vulnerable. For example, the BMP-3 – the newest Russian infantry fighting vehicle – has just 35 mm of armored plating at most, and as the abovementioned data shows, can be defeated by the GAU-8 even from the front front.
So, does GAU-8’s inability to defeat modern tanks mean that the A-10 and its gun are useless? Absolutely not.
First off, the aircraft can carry an array of other weapons – such as precision-guided bombs and missiles – that can rip modern tanks to pieces.
Most importantly, MBTs are far from being the only viable targets for the A-10. Armored personnel carriers (APCs), infantry fighting vehicles (IFVs) and other kinds of military hardware have much less armor than tanks and can be penetrated by high-explosive shells of the A-10. Unarmored targets, such as supply trucks, are even more vulnerable.
So, while the GAU-8 lost its anti-tank potential decades ago, it remains an effective weapon against a lot of battlefield targets.
Armor scheme of an early variant of the T-72, arguably the most numerous late-Soviet and modern Russian tank. The sides of its hull are 80 millimeters thick, and the sides of its turret are 290 millimeters thick: no match for the Gau-8. (Image: Tankograd)
2. The A-10 destroyed over 900 tanks in the Gulf War
The Gulf War, waged by the US-led coalition against the Iraqi forces in 1990-1991, put the A-10 in the spotlight. The aircraft featured in countless media reports from the operation, finally doing what it was designed for: attacking Soviet-made tanks.
The claim that the Warthog destroyed more than 900 (987, to be precise) Iraqi tanks is ubiquitous. Hardly any article about the A-10 fails to mention the number.
It is also one of the biggest misconceptions about the war and about the A-10 that ever existed.
The number – 987 – actually indicates how many tanks were claimed as destroyed by A-10 pilots during the campaign. It was featured in early reports by the US Central Command (CENTCOM) and somehow found its way into the minds of the public.
Later assessments found it to be overstated, with post-war analysis indicating that the number should be roughly three times lower.
Interestingly, we still don’t know the exact number of Iraqi tanks destroyed by the Warthog. The statistics were omitted from the Air Campaign evaluation because determining the exact number of A-10 kills is extremely difficult.
Independent assessments conducted by the Central Intelligence Agency (CIA) and the Defense Intelligence Agency (DIA) put the number of tanks A-10 destroyed at around 300. However, those assessments were not nearly enough to put this myth to rest.
Overstating enemy losses is a tradition as old as warfare itself. In addition, determining if an enemy is actually destroyed is often very difficult; extreme speeds and distances of aerial warfare only exacerbate that. During WWII, post-battle analyses sometimes showed that only around one-tenth of claims, made by the pilots of tank-busting aircraft, were true.
The discrepancy between the claimed and the confirmed tank kills led to heated disagreements between the USAF and the US Army after the end of the Gulf War, leading to many reports omitting precise numbers and making do with approximations.
Those discrepancies were evident from the first days of the campaign, as the CIA and the DIA, who were monitoring the results of coalition attacks, routinely dismissed the majority of USAF claims. A provisional rule was developed: the attrition of the Iraqi army was calculated by assessing only a certain part of pilots’ claims as credible.
For example, the claims by the pilots of the F-111 strike jet were divided by two. The claims by the pilots of the A-10 were divided by three.
Post-war analyses show that the results, obtained with the application of such provisional rules, were roughly correct, putting the probable number of actual tanks destroyed by the A-10 at around 300.
Several independent agencies did their own studies of the damage inflicted by coalition strikes. They showed that the claims of tank kills, presented in the CENTCOM reports, exceed the total number of tanks possessed by the Iraqi forces, and greatly exceeded the number of tanks destroyed during the campaign. The results of the studies differed as well, corroborating between 20% and 50% of the claims made in the initial reports.
Some claims were easier to assess than others: for example, footage captured by targeting systems of certain aircraft – such as the F-111 and the F-117 – could be used to assess their effectiveness. The A-10 did not have such systems.
This, along with the disagreements within the US armed forces and some lapses in documentation, led to the statistics of the targets destroyed by the A-10 being excluded from major post-war reports. And so, 987 destroyed tanks – the claim made by the pilots – remained the only hard number associated with the A-10’s involvement in the Gulf War. It was incorrect, but that fact did not receive widespread attention.
1. A-10 was built around its gun
This is, without a doubt, the most persistent and most widespread myth about the aircraft. It is not easy to determine what is actually meant by the phrase ‘A-10 was built around its gun’ – it could be that the gun was designed first and then the aircraft was created to accommodate it, or that shooting the GAU-8 was envisioned as the main operational use of the jet. In both cases, it is not true. Let’s dive into the history of A-10’s development to confirm that.
The development program for what later became the A-10 was named the A-X and started in 1966. It called for a CAS aircraft which would be armed with some sort of direct-fire anti-tank weapon – either a cannon or a recoilless rifle of yet-undetermined model.
So, Fairchild Republic and Northrop – the two companies chosen to build competing versions of the A-X – began designing their jets with consideration that something is going to be placed in its nose, but having little knowledge of what that was going to be. At the time they began working on the prototypes, the USAF was still considering whether to design an entirely new gun or use an existing one – such as the Swiss-made Oerlikon 304RK or the VRFWS-S (an early prototype of the M242 Bushmaster).
General Electric and Philco Ford were chosen to offer their designs for the gun in late 1971, but those designs were still far from being ready by May 1972, when the YA-9 and YA-10 – the two competing prototypes of the new attack jet – began flying. So, they entered the testing program fitted with GE M-61 20 mm cannons to substitute for the new gun.
The YA-10 was selected in January 1973. It wasn’t until June 1973 that USAF completed the trials of the guns and chose the GE design over the ones by Philco Ford and Oerlikon. And it wasn’t until February 1974 – a year and a half into the flight testing program – that a prototype of the A-10 was fitted with the GAU-8 for the first time.
So no, the A-10 was not designed around the GAU-8 in a literal sense. But what about the metaphorical one?
That has a bit more weight. The idea of attacking armored targets at close proximity to friendly troops was at the core of the program when it was being envisioned, and the Requirements Action Directive, which set the A-X program in motion in 1966, already included internally mounted guns with firepower equal or greater than four 20 mm M-39 canons.
However, that was not the only requirement and, along with the CAS role, the A-X had to perform other kinds of ground attack. The request for proposals USAF issued in 1970 did not even include a gun, but required the aircraft to carry at least 9,500 lb (4,309 kg) of ordinance.
While a gun (or at least a recoilless rifle) was always in mind during the design of the jet, at no point was it envisioned as its only armament. The USAF simply needed an attack jet which could do everything earlier attack aircraft did, but better. Carrying a massive gun was just one of the ways to fulfill that objective, and the GAU-8 was just one of the candidates for that position as the aircraft was being designed.
So, just to reiterate: no, the A-10 was not built around its gun. It was designed to accommodate a gun – in common with many aircraft. But the aircraft came first.