High-speed tank destroyer
The inability to install a 75-mm howitzer on the chassis of a light tank M3 Stuart upset the American military, but did not lead to abandonment of the desire to get a high-speed armored vehicle with good firepower. At the end of 1941, the T42 project appeared, during which it was planned to equip any light tank with a 37 mm anti-tank gun. True, by that time it became clear to everyone that a gun of this caliber would become obsolete even before the end of the tests of the new self-propelled gun. For this reason, the T42 documentation remained in the early stages of development and preparation. Nevertheless, a number of developments, in particular on the layout of the armored wheelhouse, were transferred to another project - the T49. This time, the chassis of the promising M9 tank was supposed to carry the 57-mm cannon, which was a further development of the English six-pound gun. In the spring of 42, two prototypes of self-propelled guns with such weapons were manufactured.
For a number of technical reasons, the second T49 prototype went to the Aberdeen Proving Ground much later than the first. In particular, and therefore, the military insisted on expanding the range of tested weapons: a 75-mm cannon was installed on the second prototype. The larger caliber gun entailed an almost complete change in the turret, as well as a number of improvements to the chassis. Due to the large number of changes, the second prototype was completed under the new T67 index. Comparative tests of the T49 and T67 clearly demonstrated the fighting qualities of the second prototype with a larger caliber cannon. At the same time, the native T67 chassis engine had insufficient characteristics, and the gun did not fully meet the requirements of the military. A more efficient 76 mm M1 cannon was installed on the SPG directly in the workshops of the test site. They decided to temporarily leave the engines the same.
ACS M18 "Hellcat" (76mm GMC M18 Hellcat) from the 827th tank destroyer battalion, which arrived with the 12th US Panzer Division in Sarrebourg, France
Tests of the updated self-propelled gun led to the fact that at the very end of 1942, the military demanded that work on the T67 project be stopped, and the entire amount of information collected should be used in the creation of a new T70 self-propelled gun, the design of which would immediately take into account all possible problems. In the spring of 1943, the first prototype of the T70 left the workshop of the General Motors plant. Five more vehicles were assembled over the next months. The armored body of the self-propelled guns practically did not undergo changes: the armor still had a maximum thickness of up to 25 millimeters. At the same time, the equipment and chassis layout have changed significantly. Instead of two Buick engines, a single 340 horsepower Continental R-975 gasoline engine was installed. To balance the machine, the transmission units were changed, and the drive wheels of the caterpillar propeller moved to the front of the self-propelled gun. With a combat weight of 17, 7 tons, the T70 self-propelled gun had a very good power density at the level of 18-20 hp. per ton of weight. On the highway, the self-propelled guns could accelerate to 60 km / h, although on tests, having made the armored vehicle as light as possible, it was possible to overcome the bar of 90 kilometers. Other stages of testing, in general, did not cause serious criticism. However, there were some complaints. So, it turned out that the new shock absorbers of the Christie system have insufficient power. I had to reinforce the front of the chassis with two additional shock absorbers. In addition, the resource of the tracks was too small, it took too much time and effort to replace the gun, and the gunner's work was hampered by poor ergonomics. Based on the results of testers' reports, the design of the T70 has been modified. The mount of the gun was changed, all its assemblies were moved two inches to the right, which significantly improved the gunner's comfort of work, and the tracks finally acquired sufficient survivability. In July 1943, as soon as all the fixes were completed, the T70 self-propelled gun was put into production. Until March 44, this ACS was produced under the original designation T70, after which it was renamed M18 Hellcat.
The crew of the armored vehicle consisted of five people, two of whom were located inside the armored hull. The workplaces of the commander, gunner and loader, in turn, were located in the tower. Due to the absence of a roof on the turret, traditional for American self-propelled guns, the crew was able to quickly leave the car in the event of a hit or fire. For self-defense, the crew had one Browning M2 heavy machine gun and, if necessary, small arms and grenades. It is worth noting that the not very spacious turret did not allow taking with you a lot of additional weapons: the main volumes were given for 76-mm shells, the packing for which contained 45 pieces, and also for ammunition for a machine gun - several belts with 800 rounds. The lack of internal volumes led to the fact that the vehicles that entered the troops were refined by the forces of the soldiers. First of all, baskets of metal rods were welded on the sides of the hull and turret. They usually kept the poor belongings of the soldiers.
76-mm self-propelled guns M18 Hellcat from the 603rd battalion of tank destroyers on the street in the French city of Luneville
A characteristic feature of the Hellcat self-propelled gun was a fairly high speed - even in combat conditions, in an appropriate situation, the car could accelerate to 60 kilometers per hour or even more. The high speed helped to compensate for the insufficient booking level. With the help of this, a lot of crews managed to escape from the blow or fire their own shot before the enemy, as a result of which they stay alive and not lose their armored vehicle. And yet there were losses, because even the frontal armor of the M18 could withstand only small arms bullets, but not artillery shells. Because of this feature, the crews of self-propelled guns had to be especially careful and rely on the range of their guns. The M1 gun, depending on the specific series, penetrated up to 80-85 millimeters of homogeneous armor from a kilometer range. This was enough to defeat most of the German tanks. As for the heavy armored vehicles of the Wehrmacht, the Hellcat tried not to engage in battle with it, not having a good advantage in position or other nuances of the battle. Thanks to the correct approach to the use of the M18 Hellcat ACS, the losses among the 2500 produced vehicles did not exceed that of other types of equipment.
ACS M18 "Hellcat" is firing at the fortified positions of the Japanese on the Shuri line
90 mm self-propelled gun M36
Simultaneously with the creation of the M10 self-propelled gun, the first research began on equipping the chassis of the M4 Sherman tank with an even more serious weapon than the 76-mm tank gun. The American military decided to follow the same path as the Germans - to equip the armored vehicle with a suitably modified anti-aircraft gun. The anti-tank gun was based on the 90 mm M1 cannon. On the chassis of the Sherman tank, a new turret with an M1 cannon was installed, which was named T7 after revision. In the spring of 1942, a prototype named T53 was tested. The new heavy turret did not allow maintaining the driving performance of the base tank, although it did provide a noticeable increase in firepower. And yet the customer, the military, rejected the T53. The design had many flaws. Moreover, the military felt that it was even worse than the previous M10.
By the end of the 42nd year, the remarks about the gun were largely corrected and two experimental guns were mounted on a tank chassis. One prototype of a promising self-propelled gun was based on an armored hull and an M10 self-propelled gun turret, while the other was converted from the M6 tank. The second prototype, due to the characteristics of the original tank, caused a lot of complaints, as a result of which all work was focused on a deep modernization of the M10 self-propelled gun, which was named T71. Even at the stage of prototype assembly, a specific problem arose. The long-barreled gun perceptibly upset the balance of the turret. To prevent the tower from collapsing under the weight of the cannon, counterweights had to be mounted on its rear side. Based on the test results of the modified M10, several conclusions were made regarding the design, as well as recommendations were made for re-equipping the serial M10 ACS with a new 90 mm caliber gun.
First prototype T71
During the last work on the T71 project, there were fierce disputes on the sidelines of the military department. Some of the military believed that the T71 had insufficient mobility and crew comfort, while others believed that it was necessary to eliminate all the shortcomings as soon as possible and begin mass production. Ultimately, the latter won, although they were forced to admit the need for improvements. Serial production of the T71 self-propelled guns, renamed the M36, began only at the end of 1943. By this time, the T7 anti-tank gun was equipped with a muzzle brake, the ring turret for the Browning M2 machine gun was replaced with a pivot mount, the internal volumes of the fighting compartment were rearranged, the ammunition racks were modified, and several dozen more minor changes were made.
During the several months during which the M36 self-propelled guns were in production, two modifications were created - the M36B1 and M36B2. In terms of their number, they were noticeably inferior to the main version. The modifications also differed in design: for example, the M36B1 - the smallest version of the ACS - was based on the original armored hull and the chassis of the M4A3 tank. In the original version, the M36 hull was welded from rolled armor plates up to 38 millimeters thick. In addition, there were several mounts on the forehead and sides of the self-propelled gun for additional booking. The hull taken from the M4A3 tank had a number of differences, primarily related to the thickness of the parts. Of particular interest is the design of the cast tower, which is the same for all modifications. Unlike other armored vehicles, the greatest thickness of the metal was not in the front, but in the back - 127 millimeters against the frontal 32. Additional protection of the front of the turret was carried out by a cast gun mask 76 mm thick. The M36 self-propelled turrets were not equipped with any protection in the upper part, however, later series received a light roof made of rolled sheets.
The combat use of the M36 self-propelled guns was quite specific. The first vehicles designed to combat German armored vehicles were delivered to Europe only in September 44th. New self-propelled guns were planned to be put into operation to replace the old M10. The small number of self-propelled guns supplied did not allow the troops to take full advantage of the new weapons. During the rearmament of the anti-tank units, an unpleasant situation arose: the old equipment could no longer cope with the defeat of the enemy's armored targets, and the production of the new one was insufficient. By the end of the fall of the 44th, a large number of German tanks on the Western Front were disabled or destroyed, which is why the American command reduced the already low rates of rearmament. The Nazi winter counteroffensive returned the M36 to its previous priority. True, it was not possible to achieve much success. The main reason for this is the peculiarities of the command tactics. The anti-tank subunits armed with self-propelled guns acted separately and did not obey a single command. It is believed that it is for this reason that the effectiveness of the use of anti-tank self-propelled artillery installations was no higher than that of tanks, or even lower. At the same time, the M1 gun had fairly high armor penetration rates - the M82 projectile pierced homogeneous armor with a thickness of up to 120 millimeters from a distance of a kilometer. The long range of confident defeat of German armor allowed the M36 crews not to enter the return fire zone. At the same time, the open self-propelled turret contributed to an increase in crew casualties in urban environments.
A column of self-propelled guns M36 of the 601st tank destroyer regiment with soldiers of the 7th Infantry Regiment of the 3rd Infantry Division of the 7th American Army on the road near the German city of Wetzhausen
"Hybrid" M18 and M36
At the very end of 1944, the idea appeared to increase the number of self-propelled guns, armed with a 90-mm cannon, with the help of armored vehicles already produced. It was proposed to modify the M36 ACS turret accordingly and mount it on the M18 Hellcat chassis. Of course, such a decision significantly hit the driving performance of the new self-propelled gun, but the production of the M36 still did not have the proper volume, and a temporary solution was needed. In addition, the M18 was supposed to become the basis for the T86 and T88 self-propelled guns, which had the ability to cross water obstacles by swimming. Prospective self-propelled guns were equipped with 76-mm and 105-mm guns, respectively. Three prototypes of the T86, T86E1 and T88 vehicles could not pass the tests - the "land" origin and, as a result, problems with the sealing of the armored hull affected.
Another version of the self-propelled gun mount based on the M18 was named 90 mm Gun Motor Carrier M18. It differed from the original Hellcat armored vehicle with a new turret with a 90 mm M1 cannon. The turret with weapons and other equipment was borrowed practically unchanged from the M36 ACS. However, it was not possible to simply rearrange the necessary units on the new chassis. The suspension strength of the M18 was less than that of the M36, which necessitated a number of measures. To avoid damage to the undercarriage, the gun was equipped with a muzzle brake and its recoil devices were modified. On the armored hull of the updated M18, it was necessary to install a support for the barrel, on which it rested in the stowed position. All design changes led to a noticeable increase in combat weight and specific ground pressure. To maintain the same cross-country ability, the 90 mm GMC M18 combat vehicle received tracks with wider track links.
The set of characteristics of the updated M18 ACS looked ambiguous. The high performance of the 90-mm cannon was "compensated" by the low speed and maneuverability of the heavy chassis. The self-propelled gun became a real compromise between weapons and mobility. The solution to the problem was seen as an increase in engine power and a change in the composition of the power plant. However, at a time when the Tank Destroyer Center and representatives of the defense industry were deciding which engine to install on the modernized M18, Germany surrendered. The need for a simple and cheap self-propelled artillery installation, which could be quickly put into production, disappeared by itself. The 90 mm GMC M18 project was closed as unnecessary.
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A characteristic feature of all American self-propelled guns during the Second World War was the use of slightly modified guns already in service. In addition, some military leaders have successfully pushed the way for the concept of self-propelled guns with a rotating turret. As it turned out after several decades, the decision was correct, although it had many unpleasant nuances of a constructive nature. For most of World War II, American self-propelled guns fought in the Pacific Islands. Fighting against Japanese tanks was very different from what the Americans would later face in Europe. Japanese armored vehicles, including the heaviest and most protected tank Chi-Ha, were confidently destroyed by almost the entire spectrum of American anti-tank artillery, including small-caliber guns. In Europe, the M10, M18 and M36 faced a much more difficult enemy. So, the frontal armor of the German PzKpfw IV tank was three times thicker than that of the Japanese Chi-Ha. As a result, more serious weapons were required to destroy German armored vehicles. In addition, the German tanks themselves carried guns sufficient to counter any enemy equipment.
It is worth noting that the development of the M10 and M18 tank destroyers began at a time when the United States had just entered the war in the Pacific theater of operations. There was no second front in Europe yet. Nevertheless, the command of the US ground forces systematically promoted the idea of increasing the caliber and power of the self-propelled guns, demanding to maintain good mobility. And yet, until the very end of the war, American designers failed to create a universal self-propelled gun that could become the guaranteed winner of any or almost any battle. Probably, the reason for this was the desire to simultaneously provide both firepower and mobility, even if at the cost of protection. An example is the German self-propelled gun "Jagdpanther" or the Soviet SU-100. German and Soviet engineers sacrificed the maximum speed of the vehicle, but they provided excellent booking and cannon power. There is an opinion that this feature of American tank destroyers was the result of requirements for equipping armored vehicles with rotating turrets. This layout of the fighting compartment simply does not allow the installation of large-caliber guns on self-propelled guns. Nevertheless, but the combat account of American self-propelled guns is a lot of units of enemy equipment and fortifications. Despite their shortcomings and problems, all American-made self-propelled guns were fully used in battles and fulfilled their tasks, which, ultimately, at least slightly, brought the end of World War II closer.
