The combat effectiveness and survivability of a self-propelled artillery installation directly depends on its mobility and mobility. A noticeable increase in efficiency can be obtained by ensuring the transfer of equipment by air with landing or parachute dropping. Similar issues were actively worked out in the past, but the lack of aircraft and helicopters with a high payload imposed certain limitations. Taking into account the needs of the army and the restrictions of military transport aircraft in the United States, a project was developed for a light ACS called the XM104.
By the mid-fifties, the US armed forces had mastered helicopters and understood their high potential. Helicopter landings showed themselves from the best side, however, the existing aviation technology made it possible to transfer only personnel and light weapons. The tanks and self-propelled guns necessary for the landing did not fit into the restrictions of the military transport aviation. In this regard, a program was launched to create promising airborne artillery installations.
One of the XM104 prototypes. Photo Ftr.wot-news.com
The study of a new issue started in 1955 and was carried out by specialists from the US Army Ordnance Tank Automotive Command (OTAC). They had to determine the optimal technical appearance of a self-propelled artillery installation with minimal dimensions and weight, corresponding to aviation restrictions, but capable of carrying a 105 mm gun. It was planned to create a self-propelled howitzer capable of firing from closed positions, and this had a serious impact on the results of the program.
A promising project of an air transportable and airborne self-propelled gun received the working designation XM104. The number for the project was chosen “in order”. The fact is that on this self-propelled gun it was planned to use the XM103 gun - a modified version of the existing experienced towed XM102. Thus, the names of various modifications of the howitzer and self-propelled guns under it indicated a certain connection between several projects in the field of artillery.
The first theoretical and practical work on the XM104 project took several years. By the early sixties, technical design began. At the same time, the project was implemented in two stages. As part of the first, it was planned to develop, build and test a simplified prototype self-propelled gun. Based on the results of his checks, the original design should be finalized and improved machines should be built. After the second stage, the XM104 had every chance of entering service.
One of the prototypes in full configuration. Photo "Sheridan. A history of the American Light Tank Volume 2"
In 1960-61, the Ordnance Tank Automotive Command and the Detroit Arsenal built two prototypes with the common name Test Rig and different numbers. They were lightweight tracked chassis with a full set of power plant and chassis units. The hulls were simplified and built from structural steel. Instead of a full-fledged gun mount, a mass and size dummy was used that imitates the XM103 product. In addition, some other units were missing from the mock-ups. For example, they did not receive a full set of crew seats, a full-fledged ammunition rack, etc.
By the time the prototypes were built, OTAC had decided on the main features of the appearance of the future ACS. The XM104 was supposed to have a length of no more than 4-4, 5 m and a combat weight of about 6400 pounds (2900 kg). She had to reach speeds of about 35 miles per hour (about 56 km / h) and overcome various obstacles; water barriers had to be crossed by swimming. Due to its small dimensions and weight, the XM104 could be transported on modern and advanced military transport aircraft and helicopters of various types. Landing and parachute landing was envisaged.
He's the top view. Photo "Sheridan. A history of the American Light Tank Volume 2"
Prototypes No. 1 and No. 2 have been tested and have shown the real capabilities of the new chassis. Taking into account the experience of their testing, OTAC engineers finalized the original project, and soon a full-fledged prototype with the required configuration was built on it. This machine was very different from the prototypes, both in terms of appearance and its equipment.
The XM104 project focused on reducing weight and dimensions. To achieve the desired reduction in the weight of the structure, it was necessary to abandon any protection. The crew was asked to be in the open area of the hull, without any protection. However, the lack of reservations was not considered a critical flaw. The self-propelled gun had to work in closed positions at a safe distance from the forward edge, which reduced the risks of shelling and reduced the need for armor.
For the self-propelled guns, an original body made of structural steel was developed, which was distinguished by a dense layout. The body was structurally divided into two volumes. The lower "bath" was intended for the installation of the power unit. She had a curved frontal sheet and vertical sides. In the center of this part of the hull was the engine, in the front part - the transmission. A box was placed on top of the bathtub, which formed a kind of habitable compartment. It was slightly longer and wider. Due to the latter, fenders were formed, which provided additional volume for the installation of various devices.
Experienced self-propelled gun in motion. US Army Photos
The power plant is based on the Ford M151 gasoline engine, borrowed from the MUTT car. 66 hp engine through a dry clutch it was connected to the Model 540 gearbox, which provided four forward speeds and one reverse. The front drive wheels received torque from a Model GS-100-3 type transmission.
On each side of the hull, four road wheels were installed on a torsion bar suspension. The rear pair of rollers served as guide wheels lying on the ground. The small diameter drive wheel was located in the bow of the side and was raised above the ground. The entire upper part of the chassis and caterpillar was covered with small metal shields and solid long rubber screens. Each track consisted of 72 tracks, 14 inches (355 mm) wide.
According to calculations, the ACS suspension could not withstand the recoil of a 105-mm howitzer. In this regard, the machine was equipped with a lowering opener. The opener itself was mounted on swinging longitudinal beams. On top of the beams and the opener, a platform was provided to simplify access to the breech of the howitzer.
The machine is in a firing position. Photo Ftr.wot-news.com
For the XM104 self-propelled guns, the 105-mm XM103 howitzer was offered. In the rear of the chassis there was a reinforced section with a seat for the upper machine tool. The gun mount was developed using existing ideas and solutions. Directly on the body there was a rotating device on which a swinging part with a barrel was placed. The design of the installation provided horizontal guidance in a sector with a width of 45 °. Vertical guidance - from -5 ° to + 75 °.
The XM103 howitzer was created by the Rock Island Arsenal on the basis of the existing XM102 towed gun. A rifled 105 mm gun with a vertical wedge breech was offered. Various prototypes of the howitzer were tested with and without a muzzle brake. In the design of hydropneumatic recoil devices, some new solutions and components were used, which subsequently became widespread. The XM103 could use all standard 105 mm projectiles and showed fire performance on par with other weapons in its class. At the same time, it was noticeably lighter than its counterparts.
XM104 is ready to fire. Photo "Sheridan. A history of the American Light Tank Volume 2"
In the aft part of the XM104 ACS, it was possible to place a compact packing for 10 unitary rounds. It is curious that the maximum rate of fire of the gun during the work of a trained crew was supposed to reach 10 rounds per minute. Thus, all transported ammunition could be consumed in a minimum time, after which the self-propelled gun needed the help of a carrier of shells.
No additional weapons were provided. One of the reasons for this was the lack of a closed case suitable for mounting a machine gun mount. It was also not possible to find a place to install an open turret. As a result, the crew had to use personal weapons as a means of self-defense.
The crew of the new self-propelled gun consisted of four people. When driving, they had to be located on their own seats at the sides of the hull. On the front left was the driver; in front of his place were the dashboard, steering wheel and control levers. There was a second seat to the right of the gun. Two more crew seats were placed directly behind the front; they were asked to ride backwards. On the sides of the seats, low flaps were provided to prevent falling overboard.
Experienced self-propelled gun XM104 in the museum. Photo US Army / army.mil
Side flaps and four seats in pairs (two on each side) were installed on hinged panels. In the stowed position, these panels lay on the roof of the hull and allowed the crew to take their places. When transferring the self-propelled gun to the firing position, the panels were folded sideways by 180 °. Due to this, the seats were removed outside the gun guidance sector, and additional platforms were formed on the sides of the hull.
ACS XM104 turned out to be very compact and light. The length of the vehicle, taking into account the gun and the opener, did not exceed 4.1 m. The width was 1.75 m, the height in the stowed position was 1.75 m. The combat weight was determined at 8600 pounds (3.9 tons). In the configuration for air transport - without fuel, ammunition and crew, but with some other devices - the mass was reduced to 7,200 pounds (3,270 kg). Driving characteristics corresponded to the calculated ones. The car could move overland at speeds up to 35 miles per hour and swim across water obstacles.
According to the known data, the first full-fledged prototype of the XM104 self-propelled gun with a full set of units was built and went for testing in 1962. Then five more cars were built with one or another difference. Thanks to this, since the beginning of 1963, six experimental vehicles were simultaneously tested at the Aberdeen Proving Ground. Thus, OTAC was able to evaluate different options for equipment and choose the most successful one. First of all, the differences affected the gun mount and the design of the howitzer.
Museum specimen, front view. Photo The Carouselambra Kid / flickr.com
Tests of six experimental XM104s continued until 1965 and ended with mixed results. First of all, the desired capabilities were obtained in the context of strategic mobility. The vehicles presented were in accordance with the restrictions of the military transport aviation; they could be transported without any difficulty by existing and future aircraft and helicopters. In the future, it was necessary to develop a parachute system for landing such equipment. Thus, the main task of the project was successfully solved.
However, the possibility of transportation by air and landing had an unacceptably high price. The car had a number of disadvantages, directly related to the reduction of its dimensions and weight. Some problems could not be reconciled, since they directly affected the fighting qualities and survivability on the battlefield. As a result, they did not allow effective use of the proposed technique in a real conflict.
View from a different angle. Photo The Carouselambra Kid / flickr.com
First of all, the reason for criticism was the lack of any protection for the crew and the vehicle's own units. The lightweight hull had to be built from relatively thin structural steel, which made it unable to withstand shelling. The crew was stationed on an open top platform and was actually covered only by side flaps of a limited area. Moreover, replacing them with armored parts would hardly significantly increase the level of protection. The open installation of the gun without shield cover also did not increase the survivability of the ACS. In addition to all this, the car in the proposed configuration could not even be equipped with an awning covering people from the sun and rain. The cover relied only on the howitzer.
The compact chassis with a relatively heavy 105 mm howitzer was poorly balanced. The vehicle had a high center of gravity due to the gun mount. This could hardly worsen the longitudinal stability, but it worsened the lateral stability. A roll of more than 20-25 ° could lead to overturning of the combat vehicle. The absence of a closed cockpit at the same time could lead, at least, to injuries among the crew.
Left side. Photo The Carouselambra Kid / flickr.com
Thus, the promising XM104 self-propelled artillery mount met a number of requirements and could show the required combat qualities. However, a number of characteristic features of this vehicle led to unjustified risks for the crew. In the proposed form, the self-propelled gun was not of interest to the army. The command of the ground forces did not want to contribute to the continuation of the work, and the US Army Ordnance Tank Automotive Command closed the project due to the lack of prospects.
Almost all of the built experimental SPGs, including the first couple of Test Rig vehicles, were dismantled as unnecessary. Only one car with tail number 12T431 was saved. It is now housed in the Fort Sill Armored Museum, Oklahoma, and is on display alongside other unique pieces of its era.
The XM104 ACS project was based on the requirement to reduce the mass and dimensions of the combat vehicle in accordance with the restrictions of military transport aviation. This task was successfully solved, but the finished sample was not entirely successful. To obtain some capabilities and qualities, I had to sacrifice others. The resulting sample had an unfortunate balance of positive and negative qualities, which is why it did not come out of the testing stage.
