High mobility is the key to the effectiveness and survivability of an artillery gun. Self-propelled artillery units look best from this point of view, but they can be too complex and expensive to mass produce. In the past, the so-called. self-propelled guns - cannons with carriages equipped with their own power plant. Such ideas have been implemented in projects in several countries. In particular, in the early sixties, the XM123 self-propelled howitzer appeared in the United States.
Until a certain time, the American army did not show much interest in self-propelled guns (SDO), preferring towed systems and full-fledged self-propelled guns to them. Nevertheless, the development of artillery and detection systems - both our own and a potential enemy - increased the importance of mobility on the battlefield. In addition, the increase in firepower, accompanied by an increase in requirements for artillery tractors, could impose certain restrictions. An acceptable way out of this situation could be a cannon with its own engine and the ability to move independently.
M114 howitzer in position. On the basis of this product was built SDO XM123, Photo by US Army
By the early sixties, the American military knew about the Soviet developments in the field of SDO, which had already entered service. The foreign idea interested them, as a result of which their own program for creating self-propelled guns was launched. For several years, defense organizations and enterprises have presented a number of mobile guns with their own power plants.
An interesting fact is that the Pentagon decided to implement the ideas of the SDO in a different way than in the Soviet Union. Soviet designers made medium-caliber self-propelled anti-tank artillery. American experts considered that in the current circumstances this does not make sense, and the LMS should be built on the basis of howitzer systems. As a result, all new self-propelled guns were intended, first of all, for mounted firing from closed positions. The first of its kind were the SDO projects with an artillery unit in calibers 105 and 155 mm.
A more powerful American-designed LMS received the working designation XM123. The first letter indicated the status of the project, and the rest were its own name. Later, as the project developed, the howitzer index changed slightly, receiving additional letters. It should be noted that the designation of the gun on the self-propelled gun carriage did not in any way indicate the base sample.
The development of the XM123 product was ordered by the Rock Island Arsenal and American Machine and Foundry. The first was responsible for the artillery unit, and also oversaw the progress of the project. The commercial organization, in turn, had to create an updated carriage. In the future, several subcontractors were involved in the project, from whom the necessary components were purchased.
In accordance with the terms of reference, the XM123 type SDO was supposed to be an upgrade option for the serial 155-mm M114 howitzer. Such a weapon has been in service with the US Army since the early forties and has already proven itself well during World War II. The last M114 howitzers were produced in the early fifties, but even a decade later they were not going to abandon them. At the same time, the creation of a self-propelled modification could extend the service life of the howitzers.
The developers of the new project decided to do without serious reworking of the existing gun and gun carriage. LMS XM123 was to be built on the basis of serial M114 units, which were proposed to be supplemented with new devices. To solve such problems, some revision of the existing products was required, but even after it it was possible to maintain the desired degree of unification. At the same time, not the most serious alteration gave the howitzer new opportunities.
Prototype XM123 in the museum. Photo Wikimedia Commons
In terms of design, the M114 howitzer was a typical weapon of its class, created at the turn of the thirties and forties. It had a swinging part with a medium-length rifled barrel, mounted on a carriage with sliding beds and wheel travel. In the original configuration, the gun could only be moved using a tractor. In fact, most of the parts of the M114 have passed to the XM123 without significant changes.
The future SDO was supposed to have a 155 mm rifled barrel with a length of 20 calibers. The breech of the gun was equipped with a piston bolt. The chamber was intended for separate loading with the supply of a propellant charge in caps. The barrel was fixed on hydropneumatic recoil devices. The rollback and knurling brake cylinders were placed above and below the barrel. The swinging artillery unit received a sector for vertical guidance. On the sides of it were balancing devices with horizontal arrangement of springs.
The upper carriage of the carriage was a cast part of a complex shape. In frontal projection, it had a "U" shape, which provided the installation of the swinging part. The rear of the machine was very high and had trunnion mounts. Also, a shield cover was installed on the upper machine. The lower machine of the carriage was made in the form of a platform on which the upper machine, wheel travel, beds and a front folding support were installed.
Carriage devices made it possible to aim the gun horizontally within sectors 25 ° wide to the right and left. The elevation angle varied from -2 ° to + 63 °. Guidance was done manually. There were sights for direct fire and on mounted trajectories.
During firing, the howitzer of the basic and modified versions relied on several points. In front of the carriage there was a triangular folding frame with a screw jack. Before firing, they went down and, with the help of an additional base plate, took on part of the weight of the gun. At the rear, on the carriage, two large welded sliding beds were provided, equipped with wide openers.
The shield cover of the gun carriage consisted of two units located to the left and right of the swinging part. L-shaped flaps were fixed directly on the carriage, on which there were hinged rectangular panels. This cover provided protection from bullets and shrapnel.
Left carriage frame with additional devices. Photo Wikimedia Commons
The need to use existing units imposed certain restrictions on the design of the XM123, but the designers from American Machine and Foundry coped with the task. All new elements designed to ensure mobility were installed directly on the existing carriage with minimal alteration. However, the resulting LMS did not differ in high mobility characteristics and ease of control.
An additional frame and a large metal casing for mounting the power plant were placed at the rear of the left frame. Inside this box were two 20 hp air-cooled motorcycle engines. from Consolidated Diesel Corporation. Both engines were connected to a hydraulic pump through a simple gearbox. Not wanting to equip the weapon with a complex mechanical transmission, the engineers used the hydraulic principle of power transmission. The pump had the means to control the pressure in the lines.
With the help of metal tubes passing along the bed and carriage, the pressure of the working fluid was supplied to two hydraulic motors. The latter were placed on the sides of the lower machine, in place of the standard wheel axles. Comparatively large motors were equipped with gearboxes with characteristic flat crankcases. Wheel drive was provided through gearboxes. It should be noted that the installation of such a power plant to some extent increased the transverse dimensions of the gun.
Next to the power plant, a folding (sideways to the left) support with a small caster wheel was placed on the bed. In the immediate vicinity of the engines, to the right of their casing, there was a metal stand with a driver's seat. When transferred to the transport position, the seat turned out to be exactly on the longitudinal axis of the carriage.
The few controls for the tool were located near the driver's seat. Control over the movement was carried out using a single lever that controls the supply of fluid to the hydraulic motors. A synchronous increase or decrease in pressure regulated the speed, differentiated - provided a turn.
On the lower machine, directly above the hydraulic motors, a pair of headlights was placed to illuminate the road when driving. If necessary, the lamps were covered with metal covers.
Modified howitzer XM123A1 in combat position. Photo Ru-artillery.livejournal.com
It should be noted that the self-propelled howitzer did not have its own means of transporting ammunition. Shells and caps would have to be moved with other vehicles.
The modernized howitzer, in general, retained its dimensions and weight. In the stowed position, the XM123 had a length of 7.3 m, width along the wheels - a little more than 2.5 m. Height - 1.8 m. Weight, depending on the configuration, did not exceed 5.8-6 tons. Thus, a pair of 20 - strong engines provided a specific power of about 6, 7 hp. per ton. Fire characteristics should have remained the same. The rate of fire is no more than 3-4 rounds per minute, the range of fire is up to 14.5 km.
In the stowed position, the XM123 SDO was similar to the basic M114 howitzer, but had significant differences. Preparing to leave the position, the calculation had to bring and connect the beds, after which it was required to raise them and lower the rear wheel to the ground. Then the driver could turn on the engine and use the lever to apply pressure to the hydraulic motors. The gun could reach a speed of no more than a few miles per hour, but this was enough to change position without using a separate tractor. Unlike Soviet self-propelled guns, the American howitzer went barrel forward.
Arriving at the position, the calculation had to turn off the engine, raise the rear wheel, disconnect and spread the beds, lower the front support and perform other necessary operations. After that, it was possible to direct and charge the howitzer, and then open fire. Transferring the XM123 from traveling to combat took no more than a few minutes.
The new SDO was not distinguished by high speed and maneuverability, as a result of which a tractor was still required to transport it over long distances. It was proposed to use its own power plant only for moving small distances between closely located positions.
XM123A while driving. Photo Strangernn.livejournal.com
The first prototype of the XM123 gun was manufactured in mid-1962 and sent to the test site. The product did not differ in high power, which limited its mobility and mobility. However, the speed of movement across the battlefield turned out to be much higher than with manual rolling. The maneuverability provided by the specific control system was not the best either. In addition, in practice, problems with the hydraulic transmission could arise, but in general, the new units coped with their tasks. In the course of further development of the project, it was possible to obtain higher characteristics.
Fire tests of the prototype ended in failure. It turned out that the presence of a large and heavy power plant on the left frame changes the balance of the gun. Recoil threw the howitzer back, but the heavier left frame was better held in place, as a result of which the gun rotated slightly around the vertical axis. As a result, after each shot, it was required to correct the aiming in the most serious way. The practical value of a weapon with such features was questionable.
Based on the results of the first tests, it was decided to radically redesign the new units. This version of the LMS was named XM123A1. The main objective of this project was to reduce the additional mass and improve the convenience of the calculation. The development of the modernized howitzer was completed at the end of 1962. In early January 1963, the A1 prototype entered the test site for the first time.
In the XM123A1 project, the hydraulic transmission and parts of other units were abandoned. Now it was proposed to use a transmission based on electrical devices. The power plant lost one of the 20-horsepower engines, and the rest was connected to an electric generator of the required power. The engine and generator were mounted on the left frame, but closer to the carriage. They were covered from above with a rectangular casing.
The lower carriage of the carriage was returned to its previous design by removing the hydraulic motors from it. The wheels moved inward a little, and electric motors of sufficient power were installed in their hubs. With the help of cables, they were connected to the driver's control system and the generator set. The control principles remained the same: a single knob controlled the current parameters and changed the speed of the motors synchronously or differentially.
To reduce the mass in the firing position, a folding wheel was removed from the left frame. Now the wheel and its support had to be removed from its place before firing and installed back when transferred to the stowed position.
Howitzer with electric transmission during test firing. Photo Strangernn.livejournal.com
The control station was located directly in front of the generator set cover. A simple metal chair with a low back was intended for the driver. Driving control was carried out with a single handle.
According to the data, in the first months of 1963, the Rock Island Arsenal and the American Machine and Foundry manufactured two experimental LMS XM123A1 and soon tested them at the test site. The driving performance of the howitzer with electric transmission remained the same, although there were some changes. Further development of existing devices could lead to improved performance.
However, the main goal of the A1 project was to correct the balance of the gun. The new units, located on the left frame, were lighter, but still too heavy. When fired, the gun still not only rolled back, but also rotated around the vertical axis. The angle of this rotation has changed insignificantly. Thus, even in a revised form, the promising LMS was inferior to the basic M114 howitzer in terms of basic operational characteristics and therefore could not be used to solve real problems.
Tests have shown that the proposed appearance of a self-propelled gun has characteristic problems, which can be eliminated only through the most serious redesign of the structure. For this reason, the customer, represented by the army, considered the further development of the project inappropriate. The work was stopped.
As part of the XM123 project, the development organizations manufactured and submitted for testing three experimental guns of two types. It is known that at least one of these weapons has survived. A prototype of the first model, equipped with a hydraulic transmission, is now on display at the Rock Island Arsenal Museum.
The XM123 self-propelled gun project made it possible to expand the capabilities of the existing howitzer, and without major reworking of its design. However, the desire to simplify the architecture of the new LMS led to the emergence of problems that led to the closure of the project. It should be recalled that in parallel with the 155-mm self-propelled howitzer, a similar system was created with a 105 mm caliber gun. The project with the designation XM124 also did not come to the end with success, but it is also worthy of separate consideration.
