Unnecessary caliber
In the period between the two world wars, artillery guns with a caliber of 57 mm seemed to war theorists, in particular in the USSR, as intermediate and unnecessary models. The destructive abilities of 45-mm ammunition were quite enough to destroy weakly armored vehicles, which included the vast majority of tanks of that time. 57-mm were not useful in air defense - 30-35 mm were enough for rapid-fire guns, and for high-altitude targets it was required to work with calibers of more than 76-mm. Among unarmored targets on land, 57-mm was frankly lacking - the high-explosive and fragmentation effect was insufficient. But in the pre-war period, Soviet intelligence obtained information about the appearance in Germany of tanks with a serious level of reservation. The Soviet response to alloyed Krupp steel was the 57mm ZIS-2 cannon, which was adopted by a decree of the State Defense Committee of the USSR in 1941. By the way, the British naval gun QF 6-pounder Hotchkiss, which the Russian Empire previously purchased, and later, in 1904, organized licensed production at the Obukhov Steel Plant, became the ideological inspirer of the designers of this gun. But back to the 57mm caliber in the ZIS-2 variant. The gun, despite the intelligence data, was not sent into mass production at the beginning of the war, since the power of the gun seemed excessive. An armor-piercing projectile of such a gun weighing 3, 14 kg at a distance of 500 meters made it possible to penetrate up to 100 mm of armor. In many ways, such power became relevant only in 1942-43, when medium tanks appeared in large quantities among the Germans. The ZIS-2 sub-caliber projectile with an initial speed of 1270 m / s generally pierced from 500 meters to 145 mm. The cannon was so successful that the head of the British mission asked for one copy to go home for review. But then the war ended, and there was little use from 57 mm - tanks often acquired thick armor, and the gun had little chance of confronting them.
In the post-war Soviet Union, however, the 57-mm did not have time to leave the scene completely - in 1955, the ZSU-57-2 tracked anti-aircraft self-propelled gun was adopted. The paired anti-aircraft machine gun consisted of two AZP-57 cannons, firing armor-piercing tracer and fragmentation tracer shells. Interestingly, the self-propelled anti-aircraft gun was designed to provide cover from the air for tank regiments and replaced the 14, 2-mm anti-aircraft gun mounts ZPU-2 based on the BTR-40 and BTR-152 in the army. Despite the fact that the total power of the ZSU salvo was very high, the vehicle showed itself weakly as an air defense tool. The point is aviation, which massively switched to jet thrust and significantly increased flight speeds. The ZSU-57-2 lacked a fire control automation system - the gunner actually determined the speed and direction of the target by eye. As a result, the 57-mm self-propelled gun for air defense was removed from production, but the AZP-57 gun itself continued to serve as part of the AK-725 ship mount. Then the anti-aircraft tracked vehicle was out of work. It was dangerous to work on armored armed targets due to the weak armor of the manned turret, and then few people thought about counter-guerrilla warfare, and even more so about the "asymmetric threat" - everyone was preparing for a global war.
But abroad, ZSU with twin 57-mm cannons turned out to be quite competitive. So, during the Vietnam War, the vehicles were in service with the VNA, successfully coped with enemy infantry and even hit tanks in side projections. This was facilitated by the armor penetration of the projectile of 80 mm, the actual rate of fire of 70 rds / min and dense thickets, which made it possible to organize ambushes. Later in the history of the ZSU-57-2 there was a series of local conflicts, where the car hit everyone with a flurry of fire, which it rained down on the enemy, but the concept did not receive any logical continuation.
57 mm at sea
In the West, in the post-war period, the 57 mm caliber was originally provided for the naval forces, and the most successful embodiment was the Swedish Bofors 57mm / 60 SAK Model 1950. It, like the ZSU-57-2, was equipped with twin cannons and also was supposed to work primarily on air targets. This gun turned out to be quite successful, many countries bought it, and the French acquired a production license and, in the modernized version of the 57 mm / 60 Model 1951, mounted it on their cruisers and destroyers. The Swedes had an attempt to build on the success and install an anti-aircraft gun on a land chassis, but the resulting apparatus with the difficult-to-pronounce name 57mm / luftvarnsfutomatkanone m / 1954 did not gain the fame of its older sister.
Although for the beginning of the 50s it was a progressive design, working in twin with a radar and equipped with a fire control system, the 57-mm did not have a decisive advantage over the more modest 40-mm Bofors cannon, and as a result, the company managed to sell only 170 guns.
Currently, the concept of a 57-mm cannon in a naval theater of operations continues to develop, and Swedish developments remain world leaders in this niche. The single-barreled Bofors SAK 57 in the latest Mark III modification is installed, in particular, by the American "littoral battleships" LCS of the Freedom and Independence type. Now the gun receives 3P ammunition, unique in many respects (Pre-fragmented, Programmable and Proximity-fuzed - pre-fragmented, programmable, with a remote fuse). More recently, a guided missile ORKA (Ordnance for Rapid Kill of Attack Craft) from British BAE Systems has appeared. For reference: Bofors lost its independence in 2000 when it passed into the hands of United Defense Industries, which, in turn, was bought by the British from BAE Systems five years later. Actually, this is where the 57-mm projectile experienced a rebirth - its form factor made it possible to accommodate complex control equipment and a fairly impressive supply of explosives inside.
The 3P projectile in the United States was named Mk. 295 Mod 0 and is loaded with 420 grams of plastic-bonded explosive (PBX) along with 2400 tungsten submunitions. Multi-mode fuse Mk. 442 Mod 0 at the head is equipped with an electronic unit and a radar, which are capable of withstanding shock overloads of 60,000 g. The projectile is constantly in radio communication with the onboard ship's fire control systems, which give it information about the flight time before the explosion and the nature of the detonation. The radar on board the 57-mm projectile is designed to create a toroidal multi-meter field around the ammunition flying towards the target. Mk.295 Mod 0 can be programmed for as many as six modes of operation - this is a real universal soldier in the hands of the navy. Modes of operation: 1. Undermining at a given time. 2. Classic pin. 3. Detonation with minimal delay, for example, inside a coast guard boat. 4. Non-contact explosion near the target based on onboard radar data. 5. The mode when contact firing is a priority, and in case of a miss, there is a controlled non-contact firing. 6. The most complex regulated non-contact detonation (the main anti-aircraft mode against missiles, attack aircraft and helicopters), that is, to cause maximum damage by the fragmentation field, a predetermined delay time for the detonation of the warhead is set in advance from the moment the proximity fuse detects the target.
But that's not all. The ORKA Mk. 295 Mod 1 projectile is based on technologies developed on the 127-mm and 155-mm Excalibur ammunition, and is capable of changing the direction of flight. In the 57 mm form factor, this is perhaps the most high-tech weapon at the moment, even if it has not yet been adopted for service. The seeker is guided by the reflected laser beam, and is also capable of identifying targets on the water and in the air by itself, referring to a pre-laid database. The combined infrared homing channel operates in the shortwave range, which coincides with the frequency of the laser channel. Just like the simplified version of the Mk.295 Mod 0, the on-board computer of the ORKA guided projectile is in communication with the ship's systems, which provide it with real-time information about the nature of the battle. There are three basic options for using the projectile: laser guidance; combined mode, when the laser first works, and then the seeker is aimed at the maneuvering target; autonomous homing according to the loaded target image - the seeker guides the projectile at the end of the trajectory. Finally, the fourth mode is shifted target designation, when the cannon hits an object equipped with laser radiation detection systems. Here, the projectile is first aimed at the laser spot near the target, and upon approach, the infrared seeker takes control of it. Interestingly, when BAE Systems presented their projectile, they considered the maneuverable boats of the Iranian Islamic Revolutionary Guard Corps as their priority targets.
57 mm on land
The idea of transferring a powerful 57-mm gun to a self-propelled land chassis was adopted by German engineers, who built an experienced AIFVSV Begleitpanzer 57 based on the Marder BMP in the midst of the Cold War. We tested the novelty until 1978, however, they considered the project not entirely promising and sent it to the back burner. The main argument was the presence of the BGM-71B TOW ATGM, which allowed the vehicle to fight tanks, and the standard 20-mm Rh-20 automatic cannon of the Marder BMP was enough to fight a series of Soviet infantry fighting vehicles.
After the Germans, the idea of re-transferring the 57-mm to the ground forces was implemented in Ukraine in 1998, when they demonstrated an BTR-80 with the good old AZP-57 cannon at the Goncharovsk training ground, in the Chernihiv region. The aiming and loading of this overly powerful gun for the chassis of an armored personnel carrier was carried out outside the fighting compartment in the open air. Obviously, after the first firing tests, the Ukrainians reasonably refused to put the machine into series.
In 2011, in Moscow, the company "Special Mechanical Engineering and Metallurgy" proposed a program for the modernization of PT-76. A 57 mm cannon was mounted on a tracked vehicle, which was renamed BM-57, and the amphibious tank itself was in the PT-2000. The idea was much more sensible than that of the Ukrainian colleagues, but it did not receive further development, primarily due to the obsolescence of the platform.
The main reason why the Russian military industry paid attention to the 57 mm was the requirements for the versatility of the main caliber. The conditions of combat use now require a prompt response to air threats, including stealth drones carrying cumulative ammunition. Naturally, for the destruction of such aircraft, not ordinary blanks are needed, but ammunition of the class of the previously mentioned Mk.295 Mod 0. In addition, in the West, traditionally light armored vehicles have armor that is resistant to the domestic 30-mm cannon 2A42 (at least in the frontal projection). which requires Russian gunsmiths to either develop new sub-caliber ammunition, or increase the caliber. And, finally, high-explosive fragmentation projectiles of a 57 mm cannon are much more effective than 30 mm, although they take up more space in the fighting compartment. In many ways, it should replace two guns at once - a 100-mm 2A70 launcher and a 30-mm 2A42 cannon. As a result, modern Russian armored vehicles will receive a universal ammunition that allows them to successfully fight the growing "asymmetric threats".
