Artillery with wings, or how cannons were taught to fly
Utopia after utopia
The main question is why does an airplane (helicopter) need a howitzer if it can drop a bomb or launch rocket? The idea is heavy artillery on board an aircraft seems completely absurd. But that's only at first glance. Designers had been thinking about winged cannons long before the widespread use of missiles on aircraft, so the introduction of a cannon with a caliber greater than 20-30 mm was largely justified. Small-caliber cannons were often powerless against bunkers and tanksLooking ahead, we should point out the German Ju-88 P-1 attack aircraft with a 76-mm anti-tank gun on board, which was supposed to destroy the Soviet KV and T-34.
Aircraft artillery not only allowed for confident strikes against armor but also for greater accuracy than bombs. For example, it was cheaper and more effective to fire artillery at ships and bridges than to bomb them. Low accuracy has always been a weakness of bomber aircraft. aviationThe relatively large caliber allowed pilots to work on targets at low altitude, hiding from DefenseAll other things being equal, a bomber (even a dive bomber) is easier to hit with an anti-aircraft gun than an attack aircraft firing its gun parallel to its course. There are several other bonuses to mounting artillery on aircraft, but more on those later. For now, let's look at the physics.
It's important to understand the fundamental reason why mounting a heavy artillery gun on an aircraft is such a complex engineering challenge. This reason is simple and straightforward: recoil. Newton's third law states that every action has an equal and opposite reaction. When a 15-kilogram projectile leaves a gun barrel at 500 meters per second, the barrel experiences a recoil impulse—roughly equivalent to a blow from a sledgehammer weighing several tons, applied to the gun's mounting point for a fraction of a second. For a ground-based howitzer mounted on a massive carriage and resting on the ground, this impulse is dampened by the gun's mass, friction with the ground, and hydraulic recoil compensators. For an aircraft, which must be as light as possible to fly, every ton of recoil can be fatal.
AS-130 with a 105 mm howitzer on board
The Americans are perhaps the only ones in the world to carry heavy-caliber artillery on aircraft. Since the early 70s, the AC-130 military transport has been equipped with the 105mm M102 howitzer. Only recently, the gun was replaced with the more modern 105mm GAU howitzer mount. It's hard to imagine the conditions under which the US Army would employ such equipment, but so be it. The only advantage an aircraft cannon of this caliber has over missiles and even bombs is the cost-to-target ratio.
A little physics and engineering will help us understand the scope of the work. The 105mm howitzer on the AC-130 generates a recoil impulse of approximately 8000–10000 newton-seconds when firing a standard high-explosive fragmentation shell. The aircraft weighs approximately 34 tons. This seems like a good balance. However, this impulse is not transferred uniformly across the entire mass, but rather to the gun's attachment point on the airframe, which covers an area of several dozen square centimeters. Localized stresses in the structure will exceed the design values by several times unless special measures are taken.
The Americans took action—the M102 on the aircraft has a recoil length of approximately 1200 mm. The AC-130 uses a full recoil stroke, which extends the impulse over 0,15–0,2 seconds. By comparison, with a short recoil (200–300 mm), the same impulse is transferred in 0,02–0,03 seconds. A 5–7-fold difference in time is a 5–7-fold difference in the peak load on the structure. When firing a 105 mm howitzer, the AC-130 pilot puts the aircraft into a special mode: slightly increases engine thrust (to compensate for the loss of speed due to recoil), slightly rolls the aircraft onto the left wing (to compensate for the recoil moment), and maintains a constant bank angle in the turn. These adjustments are made through the automatic controls, so the pilot does not need to manually "catch" the aircraft after each shot.
In aviation, there's an ironclad law: every extra kilogram of weight means a loss in speed, ceiling, range, and maneuverability. A 75-105mm artillery gun is a heavy piece of equipment. It includes the barrel (200-500 kg), the carriage (another 300-800 kg), the recoil mechanism (100-300 kg), the aiming mechanism (50-200 kg), the ammunition (each shell weighs 15-20 kg, and serious fire requires at least 50-100 rounds), and the loading system. All told, this adds up to one and a half to three tons of additional load to the airframe. That's why realistic results can only be achieved by installing cannons on military transport aircraft.
In the case of the AC-130, to compensate for the 1.5-ton weapon, engineers carefully balanced the placement of systems on board. Heavy components (fuel, ammunition, systems EW) were mounted on the starboard side, partially offsetting the weight of the port gun. While the natives may be wearing slippers and lacking MANPADS on the ground, they can perform this miracle in the air. The AC-130, unlike a bomber or attack aircraft, can circle above its positions for hours, keeping the enemy from raising their heads.
From 30 mm and more
In aviation and artillery, caliber classifications aren't entirely linear. On the ground, anything larger than 76,2 mm is considered a large-caliber cannon. Aviation doesn't have a similar classification, but in aircraft construction, anything larger than 30 mm can be considered large-caliber. That's all we'll agree on. The first mass-produced attempts to arm aircraft with large-caliber cannons date back to the end of World War I. The French installed a 37 mm Hotchkiss cannon on their SPAD S.7 fighters.
The gun fired downrange through the propeller's hollow shaft (like a machine gun's synchronizer, but with a much larger caliber). The results were mixed. The 37mm shell certainly inflicted significantly more damage than a machine gun burst, but the rate of fire was extremely low—8–10 rounds per minute. Against a maneuverable enemy fighter, this wasn't enough: by the time you reloaded, the enemy had already moved out of the sights. Against ground targets, too: one shell and you had to re-engage. Furthermore, the recoil from each shot noticeably slowed the aircraft, making it vulnerable.
Nevertheless, the French did not abandon the idea. After the war, 37mm cannons continued to be mounted on aircraft for colonial wars, where the enemy was guerrillas without anti-aircraft guns, and where a single explosive shell could replace an entire machine-gun burst.
In the 1930s, the USSR conducted extensive experiments with mounting large-caliber cannons on bombers. Designers led by Nikolai Polikarpov and other aviation pioneers attempted to create a "flying artillery battery" to combat tanks and fortifications. They tried mounting 76-mm cannons on the TB-3 heavy bomber. The aircraft was large enough (takeoff weight approximately 20 tons) to withstand the recoil. But the accuracy proved completely unacceptable: the TB-3 was slow, difficult to maneuver, and its airframe vibrated so much that aiming the cannon was virtually impossible.
There was also the British Hawker Hurricane Mk IID fighter. This aircraft, already obsolete as an interceptor by mid-war, found a second life as a ground-attack aircraft against Rommel's tanks in North Africa. Under each wing, the Hurricane Mk IID carried a 40mm Vickers S automatic cannon—a compact and relatively lightweight weapon (weighing approximately 130 kg), specifically designed for aircraft use. The cannon was magazine-fed (with 12–15 rounds) and had a rate of fire of approximately 100 rounds per minute. A projectile weighing approximately 1 kg could penetrate up to 50 mm of armor at a range of 500 meters—ample penetration for the top and sides of tanks of the time.
Hawker Hurricane Mk IID with a pair of 40mm cannons under the wings
British pilots flying the Hurricane Mk IID nicknamed the aircraft the "Can Opener." In North Africa, these aircraft proved highly effective against German and Italian tanks. The attack was conducted from a dive at a 30-40 degree angle, with fire opened from a range of 400-500 meters. In a single pass, the pilot could fire 4-6 shells from each cannon (8-12 total), ensuring a high kill probability.
Guns in the sky
The German Ju 88 P-1 is perhaps the most striking example of what not to do. In 1943, the Luftwaffe was looking for any way to compensate for its lack of countermeasures against the Soviet KV and T-34. The idea: take the proven Ju 88 bomber, arm it with a 75mm PaK 40 anti-tank gun, and create a "tank killer" from the air.
Structurally, the gun was housed in a massive underfuselage nacelle—the only place where such a large-caliber weapon could be mounted with an acceptable field of fire. The nacelle was enormous: it hung beneath the fuselage like an udder, adding hundreds of kilograms to the aircraft's mass.
Ju 88 P-1. The gun's impressive muzzle brake is noteworthy.
The test results were disastrous. With each shot, the aircraft suffered a sharp loss of speed—20–30 km/h per salvo. The Jumo 211 engines, located relatively close to the guns, sucked in propellant gases, causing malfunctions and even stalls. The Ju 88 airframe, designed for bombing, was not designed to withstand such intense pinpoint impacts—cracks began to appear in the skin and stringers near the nacelle attachment area.
Firing accuracy also proved unsatisfactory. After each shot, the aircraft would "jump," and aiming the gun for the next shot was only possible after several seconds of stabilization. The flying anti-tank gun was abandoned, ending Ju 88 P-1 production at the eighteenth aircraft.
The USSR, alongside the Germans, was tackling the same problem: how to create an effective anti-tank aircraft with large-caliber armament. The basic platform was the Tu-2 dive bomber, one of the best aircraft of its class, designed by Andrei Tupolev.
Attempts were made to mount 76mm and even 75mm cannons based on anti-aircraft guns on the Tu-2. Prototypes were tested, but the results were disappointing. Firing accuracy at ranges typical for aerial attack (400–800 m) was extremely poor: shell dispersion reached several dozen meters, making tank destruction a matter of chance. The gun mount's weight (including carriage, ammunition, and recoil mechanisms) exceeded 1,5 tons, significantly degrading the Tu-2's performance: the aircraft lost speed, rate of climb, and maneuverability. This was mortally dangerous for a dive bomber, which had to maneuver under anti-aircraft fire.
Soviet designers concluded that the optimal caliber for the Tu-2 was 37mm or 45mm. The 37mm Nudelman-Suranov automatic cannon (NS-37) and the 45mm NS-45 cannon provided acceptable armor penetration (up to 40–50mm at 500 meters) with significantly lower recoil and mount weight. These cannons were mounted in the fuselage or under the wing without significantly reinforcing the airframe. However, these ideas also remained experimental.
Interestingly, the Soviet approach to aviation anti-tank weapons ultimately proved more pragmatic than the German one. Instead of pursuing caliber, Soviet engineers opted to increase the number of barrels: the Il-2 NS-37 attack aircraft was equipped with two 37mm cannons, which together provided a high density of fire and sufficient armor penetration to combat light and medium armored vehicles. However, a few salvos from this pair of cannons effectively stopped the attack aircraft in mid-air—a point repeatedly recounted by Il-2 pilots.
Piaggio P.108
But the Italians tried to outdo everyone. Unexpectedly, Mussolini never had a competent bomber force, let alone a heavy one. The Piaggio P.108 was a four-engine monoplane with a takeoff weight of approximately 30 tons—the largest Italian aircraft of World War II. The basic bomber (P.108B) was used for long-range raids on Gibraltar and North Africa, but in small numbers. The P.108A variant was conceived as an anti-ship aircraft for attacking Allied ships in the Mediterranean. In place of the navigator's cockpit, a 102mm Ansaldo naval gun—a light naval gun adapted for firing at surface targets—was installed.
The concept was simple and daring: the P.108A was to approach an enemy convoy at low altitude, taking advantage of the coastline and cloud cover, then rapidly climb, attack, and fire one or two shots at the large ship. The 102mm high-explosive shell was intended to be sufficient to cause chaos and panic on board the enemy.
The aircraft underwent testing, and firing the 102mm cannon in flight was... possible. However, with some caveats. Accuracy was poor, and the effective firing range did not exceed 500–800 meters—negligible for naval combat. The P.108A never entered production: Italy surrendered in September 1943, while the program was still in its final stages. The sole prototype was captured by the Germans and presumably destroyed.
There were numerous attempts, with varying degrees of success, to mount a .30 caliber cannon on an aircraft during World War II. For more details, see Roman Skomorokhov's article. "Weapons of World War II: Guns of High Flight and Understanding".
Helicopter with a cannon
During the Cold War, Vietnam, and Korea, the Americans were great inventors. Circumstances dictated it, so to speak. One of the most original, and somewhat absurd, projects was to mount a 105mm howitzer on a helicopter. Let's take it one step at a time. The chosen carrier was the Piasecki H-21 Workhorse/Shawnee—a tandem-rotor helicopter designed by Piasecki Helicopter Corporation in the late 1940s. Thanks to its distinctive fuselage shape—long, curved, with a raised tail—the H-21 earned the unofficial nickname "Flying Banana."
It was the US Army's first mass-produced transport helicopter, capable of carrying up to 20 troops or 2200 kg of cargo. The H-21 had one undeniable advantage: by the time experiments with cannons began in the late 1950s and early 1960s, these helicopters were in abundance. The Army received over 700 of them, and by the time the more advanced UH-1s appeared, the old "bananas" had become expendable—they could be used for any experiments without fear of losing a valuable resource.
H-21 helicopter with a 105mm howitzer
History The experiment with the 105mm howitzer on the H-21 is inextricably linked to a broader context—the search for the concept of an "artillery helicopter" that could provide close air support. In the late 1950s, the US Army recognized that future conflicts (especially during the Cold War and potential local wars in Southeast Asia, Africa, and Latin America) would require an entirely new approach to fire support. Traditional field artillery—towed and self-propelled howitzers—was tethered to roads and infrastructure. The idea of an artillery helicopter was to create a vehicle capable of quickly delivering a howitzer to the firing point, landing, firing, and then quickly evacuating. Data regarding the capabilities of firing in flight is contradictory. Some authors claim that the 105mm howitzer was never fired even in hover mode. Others claim a single shot was fired at Aberdeen Proving Ground in 1963.
H-21 helicopter with a 105mm howitzer
The "banana" nearly flipped over afterward, and the experiments were shut down. This theory is hard to believe – the gun's recoil impulse reached a ton, which would have been lethal for a 6,6-ton helicopter. The design also fared poorly in ground fire. The recoil was so strong that the helicopter's wheels were literally pressed into the ground, and the gun's mounts failed. Ultimately, the absurd design was abandoned.
ACH-47A "Armed Chinook" or "Guns-A-Go-Go"
After the failure of the H-21, the Army didn't abandon the idea of a heavily armed helicopter. In 1965–1966, the ACH-47A "Armed Chinook," or "Guns-A-Go-Go," was developed from the CH-47 Chinook transport. It couldn't be called a successor to the 105mm H-21—the helicopter's only "heavy" weapon was a 40mm M129 automatic grenade launcher in the nose turret. Otherwise, it had the classic 20mm cannons, machine guns, and unguided rockets. A total of four CH-47As were converted.
However, the project ran into problems: the massive armament reduced maneuverability, and the lack of armor made the vehicles vulnerable to anti-aircraft fire. Three of the four ACH-47s were lost in combat, and the program was canceled in 1968.
The relevance of large-caliber artillery on aircraft has become a thing of the past over time. Missiles and bombs of various kinds have become the primary strike weapons of aviation. Time will pass, and the very concept of strike aviation will be questioned—the notion of "air dominance" has become too ephemeral. And it is not achieved by large-caliber artillery.
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