[Popular Science of Chinese Military Technology] From "nothing to nothing" to "hitting the target from a hundred steps away", the evolution of tank artillery aiming

In the brutal trench warfare of World War I, both the Allies and the Central Powers conducted their own tank designs and experiments, and the first tank-to-tank battle in human history broke out. Tanks, as a fairly effective anti-tank weapon, have entered the vision of various countries. However, affected by gravity, the trajectory of the tank's main gun must be curved, and the slower the ammunition flies, the more curved the trajectory will be. In the task of supporting infantry, a second calibration shot can be performed if the first shot misses. In the brutal tank battle, the sturdy tank can become a "steel coffin" at any time, so accurate distance measurement is very necessary.

Vision! Vision is the key!

As a solution for early tanks, memorizing and comparing the size of the target became an important solution. As early as the Middle Ages, users of siege machinery had learned to use their thumbs to roughly measure the distance to the target. This system was later replaced by more accurate fine-position ranging, and has been used in all modern military telescopes. To achieve fine-position ranging, it is necessary to measure the width of the target in the field of view, and then compare it with the known actual size of the target to roughly estimate a distance. This method of observation is widely used by artillery and is naturally applied to tanks. However, it is naturally not easy to stretch your arms in a narrow tank. Using a telescope to measure distance requires both memorizing the size of the target and making accurate measurements in a bumpy tank, which is very difficult.

(The picture shows the distance measurement scale of the M2/M3 infantry fighting vehicle. Source: expert data map)

In order to solve these problems, reticle ranging came into being. As an alternative to fine-position ranging, reticle ranging selects a common target size: for example, for the 1.7 meters from the top of the human head to the bottom of the feet, or the height of a tank of 3 meters, a ground line and a diagonal line are drawn to aim at the bottom and top of the target respectively. If the bottom of the target coincides with the ground line, and the top happens to be at the same height as a certain point on the diagonal line, the reading above can be read and used as a reference for shooting. This ranging method is widely used, is quite simple to manufacture, has relatively accurate ranging, and is also very convenient to use. Most tanks during World War II used this ranging method, which can quickly and accurately obtain the distance to the target tank.

(The picture shows the 1P59 scope in the game, which can be used to measure distance by adjusting the magnification. Image source: Bilibili)

With the advancement of optical technology, some more advanced reticle distance measurement methods have also been developed. Some tanks and anti-tank guns use optical sights with adjustable magnification, which can scale the size of the target in the field of view. In this case, you can use a non-zooming eyepiece board with a circle drawn on it. When the target tank can be put into the circle, the zoom magnification will just correspond to the correct distance. Through this method, the sight will also be at a magnification that is more suitable for aiming, and you can even set another reticle to be linked to the magnification adjustment. Once the target is put into the circle, the center of the circle is just the preview point of the parabolic trajectory, and it can be fired directly, and the reaction speed is much faster.

Machines! Solve problems with machines!

However, both the zoom ratio and the general reticle face the same problem: they can only shoot at the "exact" target tank. If the reticle is designed for the tall "King Tiger" tank, but needs to hit the Type 94 "Bean Tank" which is only as tall as a person, the ranging will be very easy to have errors, and it is difficult to correct. At the same time, the accuracy of the reticle ranging is also relatively limited. For armor-piercing projectiles with a higher initial velocity, the outer trajectory approaches a straight line, the calculation difficulty is relatively low, and the hit rate is acceptable. If a powerful grenade is fired, its accuracy is almost not of practical use value. For this reason, various countries have launched research on the installation of rangefinders on vehicles.

(The picture shows the 15-meter baseline rangefinder on the Japanese ship Yamato, which has good accuracy in long-distance measurement. Image source: Sohu)

The history of mechanical rangefinders is long, from the handheld rangefinders during the Sino-Japanese War to the combined image and stereoscopic rangefinders during World War I, it has gone through half a century. During World War II, a series of mechanical rangefinders with faster response speeds, such as air rangefinders, appeared and were widely equipped in the navy. However, both stereoscopic rangefinders and combined image rangefinders require that there should be a considerable distance between the two observation points in order to calculate the distance through the angle difference of the lens. For the navy, the distance between the front and rear masts is naturally sufficient, and it is not a problem to directly install an ultra-wide device. But for the army, the tank is less than 4 meters wide, and even if the rangefinders are arranged at both ends of the tank, the accuracy is not ideal.

(The picture shows the distance measurement method of the optical rangefinder, the upper one is the combined imaging method, and the lower one is the stereoscopic method. Image source: Zhihu)

Both the United States and Nazi Germany made attempts in this regard during World War II, trying to install a rangefinder for tanks to ensure the ability to engage in long-distance combat, or to go further, to directly link the rangefinder reading to the elevation control of the gun, and automatically bind the scale for long-distance shooting. This design became more popular after World War II. The Soviet Union once installed an independent combined-image rangefinder for the commander on the Su-122-54 self-propelled artillery, which was used for the commander to measure the distance and report to the gunner during combat. The United States used a stereoscopic rangefinder on the M48 tank, but although the stereoscopic type is more accurate than the combined-image type, it requires more training and is more prone to visual fatigue. In the subsequent improved version, it was changed to the combined-image type. France set the lens position of the rangefinder at both ends of the turret of the AMX-30 tank, allowing the rangefinder to run through the entire turret to achieve the maximum distance measurement baseline length.

Echo! Echo ranging is the correct answer!

Although countries tried to install optical rangefinders on tanks in the early days of the Cold War, the automation level of optical rangefinders was too low, and shooting accuracy mainly depended on the proficiency of the person. It can still play a good effect in static-to-static shooting, but the effect is very poor when facing targets with height differences and shooting moving targets. At the same time, the ranging accuracy of the optical rangefinder is low. The error of the combined imaging rangefinder with a baseline of 1-1.5 meters can reach plus or minus 7% within 6 kilometers. If there is a height difference between the target and the tank, it is easy to miss the target. In order to solve this problem, scientists from various countries chose to "hit" the enemy tank first and then obtain the distance.

The earliest bullets used to "hit" enemy tanks were machine gun bullets. The British coaxially fixed a 12.7mm heavy machine gun near the artillery, using special bullets, and the trajectory was close to the artillery trajectory. The special range-finding bullet fired will emit light at a specific distance. The approximate distance can be obtained by calculating how many times the ammunition emits light before hitting. The trajectory of the machine gun can also be used to estimate whether the artillery aiming point is too low or too high. If the machine gun bullet can just hit the tank, then the artillery bullet trajectory will be similar. This design is also used in infantry recoilless guns, which use 12.7mm range-finding guns to fire. If the tank can be hit, it means that the trajectory is accurate, otherwise it needs to be adjusted. However, the sound of the 12.7mm machine gun firing is not small, and after hitting it, it will definitely expose the target. The enemy will do everything they can to evade, and the gunner will have to re-aim to hit the target with the main gun.

(The picture shows a T-62 tank equipped with a radar rangefinder. Image source: Baidu Post Bar)

After the attempt to hit the target with a "bullet", the next step was to try to "hit" the target with radar waves. The Soviet Union experimentally modified several T-62 tanks and installed huge radar transmitting antennas. In theory, as long as the radar is aimed at the enemy tank, the echo of the metal tank will be reflected to the transmitting source, and the distance between the tank and the target will be calculated based on the time required for the echo. It should be said that the Soviet attempt was almost successful. The radar ranging tank has a ranging speed far exceeding that of the optical rangefinder. In theory, the radar rangefinder can be directly linked to the tank artillery, which is very convenient for ballistic calculations and artillery posture adjustments. However, the size of the radar rangefinder is quite large and the production cost is also high. The exposed radar antenna is very easy to be destroyed by heavy machine guns or even rifles, and it is completely impossible to use it as a consumable.

(The picture shows the daytime gunner's telescope installed on the T-72 tank, which integrates the laser rangefinder function. Image source: Zhihu)

Finally, laser became the most practical means of rapid distance measurement. Due to the small size of the laser source, the power of the ranging laser is relatively low, and it can be easily integrated into the fire control system of the tank. The tank emits a laser beam at the target, and the target will naturally produce a laser reflection, which will be captured by the receiving end of the rangefinder. The distance between the target and the target is calculated based on the time required for the laser to "hit" the target. Although the propagation speed of light is extremely fast, it is no longer a problem for the electronic technology of the Cold War. However, the laser rangefinder is not perfect. After all, the laser of the tank is scattered. If it passes through leaves and grass, laser echoes will also be generated on the grass and captured by the rangefinder. When facing a more complex environment, the tank gunner needs to choose the echo correctly. For example, when facing an enemy tank in a dense forest, the second echo can be selected to filter out the laser reflected by leaves and obstacles, and obtain the correct distance tank parameters. At the same time, since the speed of laser ranging is extremely fast, if there is a problem with the ranging accuracy, the distance can be measured again until a reliable distance value is obtained.

The problem of tank range finding was finally solved through the continuous invention of new technologies over the past century. In adjusting the vertical posture of the gun, the tank finally had the ability to automatically calculate the lead time. However, calculating the lead time in the horizontal direction is much more difficult.

Produced by: Science Popularization China

Producer: Guangming Online Science Department

Author: Huang Tian (Caidongqing Science and Technology Innovation Team)

Review expert: Liu Xiaofeng (senior military science writer)

Planning: Jin He